Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies (2020)

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62 Survey of Transportation Managers Methods The research team created a survey with 28 questions using Qualtrics, which were emailed in the fall of 2017 to a list of approximately 50 project contacts, including representatives from many transportation authorities, primarily states. These professionals were asked to share the survey with colleagues to increase participation in the survey. The team also asked specifically for email addresses of contacts project contacts felt could contribute additional information to our study (e.g., GIS managers), which grew the contact list to over 130 professionals. The following text introduced the survey: “The Monarch Joint Venture, with funding from the National Cooperative Highway Research Program, is developing tools for managers of roadside ROWs to provide habitat for monarch butterflies. These tools include 1) models for where to place or maintain habitat, 2) field assessment techniques, 3) habitat quantification tools, and 4) forums for selecting best management practices. We have a few questions for you as a transportation professional that will help us to design these conservation tools.” The survey questions and multiple choice answer selections (where applicable) are listed below. Survey Questions Overview 1. Name, email address, organization, state. 2. What geographical jurisdiction best describes your work? (state, larger than state, smaller than state) 3. Does your organization provide habitat for pollinators, such as flower plantings, on some of your road rights-of-way? 4. Give a brief description of your organization’s habitat program for pollinators or monarchs. 5. What best characterizes how your organization currently determines where to put habitat plantings? (work in GIS, have a process but it does not use GIS, we do not have a standard process) 6. Which of these would be helpful to your program? (guidance where to install habitat plantings or manage current habitat, tools for monitoring vegetation to assess habitat quality, both, other (write-in available)) Geographical 7. What road length unit would be most useful in a model that helps roadside managers identify better places to develop monarch habitat along roadways? (¼ mile, ½ mile, 1 mile, 5 miles, 10 miles +) C H A P T E R 6 Product D: Best Management Strategies and Decision Support

Product D: Best Management Strategies and Decision Support 63 8. Does your organization have any maps of levels of winter salt application on various road- ways? (yes, no, in development, n/a, I don’t know but you could contact (write-in)) 9. Does your organization have a map of where noxious weeds occur within the road- side rights-of-way? (yes, no, in development, n/a, I don’t know but you could contact (write-in)) Rights-of-Way Width 10. Are you familiar with the widths of the roadside rights-of-way in your jurisdiction? – If yes, continue through next questions – If no, skip forward 11. Can you estimate the width of the roadside habitat on these road types? Please estimate the distance from paved edge to right-of-way edge, on one side of road, in feet. – Interstate and other large highways and freeways – State or smaller highway – County or moderate roadway – Local road Field Assessment 12. For field visits to assess good potential sites identified in the habitat model, what length of road would it make the most sense to evaluate in a visit? (less than ¼ mile, ¼ mile, ½ mile, 1 mile, 5 miles, 10 miles +) 13. Do you direct or manage a roadside management crew? – If yes, continue through next questions – If no, skip forward 14. Would you have personnel or interns who could conduct field assessments of potential monarch habitat in the roadside corridor? (yes, no, maybe) 15. How many people would you have who could conduct field assessments of potential road- side monarch habitat? (1, 2–4, 5–9, 10+) 16. How many days do you estimate these people might be able to assess habitat? (one to five days/yr, six to 10 days/yr, one-half day/week, one day/week, one day/month) 17. Would your crew be able to identify noxious weeds that require management? (yes, no, maybe) 18. Would your crew be able to learn how to identify milkweed plants that are important to monarchs? (yes, no, maybe) 19. If your crew was assessing a site for its suitability for development into monarch habitat, how long could they spend assessing the site? (<30 minutes, 30–60 min., 1–3 hours, 4–6 hours, 6 hours +) 20. If your crew was monitoring existing pollinator plantings to assess the quality of the habitat for monarchs, how much time could be spent per site? (<30 minutes, 30–60 min., 1–3 hours, 4–6 hours, 6 hours +) Management Questions 21. Do you manage noxious weeds along your roadways? – If yes, continue through next questions – If no, skip forward 22. Can you briefly describe the approach or techniques employed in your jurisdiction in controlling noxious weeds? 23. If there is a guidance document, can you provide the link to that? 24. Can you estimate what percentage of the roadways in your jurisdiction is managed for noxious weeds? (<5%, 5–25%, 51–75%, >75%)

64 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies 25. Can you answer questions about roadside mowing practices in your area? – If yes, continue through next questions – If no, skip forward 26. Is there a consistent mowing schedule throughout your jurisdiction or does it vary among road types or vegetation types? (yes; no, it varies by region; no, it varies by road type; no, it varies by county; no, it varies by more than one factor) 27. How frequently are the interior edges (to maintain sightlines) of the roadways mowed? (monthly or more during growing season, every 6–8 weeks during growing season, other (write-in)) 28. How frequently are the entire widths of the rights-of-way mowed? (3+ times per year, 1–2 times per year, once every 2 years, once every several years, typically not needed, other (write-in)) Open Input What guidelines or products would you find most helpful? (a model of where habitat may exist for monarchs, a model of where it may be good to develop for monarchs, field protocols for managers to assess field habitat, a habitat calculator to depict habitat quality for monarchs, information about best management practices for monarchs, other (write-in)) Please share any comments or questions about the project. Survey Results The team received 79 responses to the survey; the majority of respondents represented states (58%) followed by counties (25%). Eight percent were regional or national, 9% local, and 5% were other entities. Survey respondents represented 19 states: Arizona, Arkansas, California, Illinois, Indiana, Iowa, Kansas, Maryland, Michigan, Minnesota, Nebraska, New Hampshire, Ohio, Oklahoma, South Dakota, Texas, Virginia, Washington, and Wisconsin. Because the survey asked questions in a variety of different topical areas that may or may not have matched up differently to areas of expertise, answering questions were optional; thus, the number of respondents varied across questions. Nearly three-fourths (74%) of the states represented indicated that they had a pollinator program (14 states). Many programs indicated that they were planting prairie or wildflowers in the ROWs and in rest areas; some programs augment with milkweed, some programs cited outreach components and vegetation management, mostly in the form of altered herbicide treatments and mowing schedules. The survey asked if managers would like guidance about where to install or manage monarch habitat, tools for monitoring that habitat, or both. Of 33 respondents to this question, 39% wanted monitoring methods, 12% indicated that the planning information would be most valuable, and 39% wanted both (9% had other answers). When asked how their organization currently determines where to manage pollinator habitat or put habitat plantings, the greatest number of respondents indicated that they did not have a standardized process (36%), 25% said they have a process that does not use GIS, and 17% indi- cated that they used GIS in this process. Managers were asked to indicate which length of road would be most relevant for their plan- ning purposes (for focus of the GIS prioritization tool). Responses varied quite heavily, from one-quarter mile to 10 miles or more (Figure 36).

Product D: Best Management Strategies and Decision Support 65 The survey asked about the availability of GIS data regarding the application of road salt. While the greatest number of respondents indicated that they did not have this information, positive responses came from six states: Arizona, California, Iowa, Maryland, Michigan, and Minnesota. Similarly, it was found that, while many respondents (47%) did not have a map of noxious weeds within their ROWs, 15 positive responses were received, and seven indicated “maybe.” Respondents in six states indicated that they had maps of noxious weeds: California, Iowa, Maryland, Michigan, Minnesota, and Washington. Most respondents did not have a map indicating ROWs widths for various road types, but a few states indicated that they did: California, Iowa, Minnesota, South Dakota, and Virginia. Road managers also offered estimates of the widths of the ROWs (one side of road, from road edge to vegetation edge) for various road types (data available on request). When asked if personnel or interns could be made available to conduct field assessments of potential monarch habitat in the roadside corridor, 22% indicated yes, 52% indicated maybe, and 26% indicated no. Most respondents (50%) indicated they would expect to be able to have two to four people who could conduct field assessments, 31% indicated they could have one person available, and 19% thought they could have a team of five of more people. Most respon- dents (41%) thought the field team would be available one to five days/year, 22% thought six to 10 days a year; other responses were half day a week, one day a week, and one day a month (three responses for each). When asked how long their field crew could spend assessing potential habitat sites, most indicated less than 30 minutes (n = 53) (Figure 37). When asked how long their field crew could spend monitoring existing habitat, answers were very similar. The survey also asked about the skills of potential field crews. Most thought that their crews would be able to identify noxious weeds that require management (Out of 32 respondents, 9% 8% 24% 10% 28% 21% Figure 36. Variety of responses in the scale of road miles that managers thought might be an appropriate length for assessing in GIS (n = 67).

66 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies there were 56% yes, 34% probably yes, and 9% no). Similarly, when asked if they would be able to identify milkweed plants, all but one respondent thought this would be possible (97% yes; n = 32). Answers to additional questions about capacity for field work and management practices are presented in Table 12 below. When asked, “Can you estimate in what percentage of the roadways in your jurisdiction there are weeds actively being managed for noxious weeds?” responses were found to be highly vari- able (Figure 38, n = 48). The survey asked about typical mowing frequencies: first, how often the safety zones or sight- lines were mowed per season. Responses were monthly or more (17%), every 6–8 weeks (26%), other (57%) (n = 42). The survey then asked about the frequency with which they mow the full width of the ROWs (Figure 39). Comments received in the survey indicated a concern among respondents about a lack of time or funding for field assessments. Similarly, there were also needs for funds to plant milkweed and other beneficial nectar species in their habitat restorations. Another comment indicated that more work was needed in improving the public perception of deferred mowing and other integrated vegetation management techniques to benefit pollinator habitat and the cost savings that they provide. Survey Conclusions From this survey, the research team gathered valuable data to guide design of the decision- support tools in the project and gained many valuable project contacts that will continue to provide value to this ongoing work. The team gained insights into the interests, capacity, and needs of transportation managers. It was learned that many managers were interested in tools for assessing where to put habitat, as well as tools for assessing existing habitat. It is feasible for DOTs to assess habitat in the field (with a preference for surveys to be quick), and to develop habitat, although time and funding were often cited as limiting factors. Figure 37. Amount of time managers indicated that the field crew could spend assessing each potential habitat site (n = 53).

Product D: Best Management Strategies and Decision Support 67 Question Survey Results Do respondents have personnel/interns that could conduct field assessments? (n=46) Yes No Maybe 22% 26% 52% How many days per year could field 10+ 6 to 10 1 to 5 Other crew(s) allocate to habitat assessment? (n=32) 9% 31% 50% 9% Could field crews identify weeds requiring management? (n=32) Definitely yes Probably yes 56% 34% Could field crews identify milkweed? (n=32) Definitely yes Probably yes 66% 31% Appropriate length of ROW for field visits. (n=64) 5+ miles 1 mile 0.5 miles ≤0.25 mi 25% 30% 22% 22% How much time could be spent monitoring a specific site? (n=52) 1+ hours 30–60 min 10–30 min <10 min 15% 28% 34% 23% Do respondents manage noxious weeds? (n=63) Yes 71% Is there a consistent mowing regime in their jurisdiction? (n=42) No, due to factors such as region, road type, etc. 79% Frequency of mowing the safety zone during the growing season. (n=42) Monthly Every 6–8 weeks Other 17% 26% 57% Frequency of mowing the full width of the ROW during the growing season. (n=42) 3+ times per year 1–2 times/yr Once every 2–5 years Typically not needed Other 5% 36% 24% 29% 7% Table 12. Responses by roadside managers to a subset of the survey questions asked regarding roadside vegetation assessment and management. 0% 5% 10% 15% 20% 25% 30% 35% <5% 5-25% 25-75% >75% Figure 38. Estimated percent of roadway in respondents’ jurisdiction treated for noxious weeds.

68 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies Hearing directly from roadside managers and other transportation professionals bridged an understanding in what barriers and limitations prevent widespread adoption in restoring native plant vegetation in roadside areas. Through asking targeted questions about decision-making processes, the team was able to tailor discussions and tool development in a way that will make them more useful to roadside management entities. Understanding the time and capacity limita- tions that managers face also emphasized for the researchers the importance of the quick nature of the assessment tools that are developed through this project. Robust scientific datasets come at the cost of a lot of time in the field and biological expertise often not encountered in roadside management entities, so robust monarch monitoring program experts were paired with the project team to simplify tools that yield valuable information that is easier and faster to imple- ment than the more robust program protocols. User Profile Interviews Methods To gain more in-depth information from managers who were already involved in pollinator habitat management within ROWs, researchers conducted interviews to learn about managers’ information and decision-support needs to augment the more general information gained from the Qualtrics survey. The research team interviewed four roadside managers with the follow- ing profiles: • Rob Roman (Roadside Manager, Engineering and Secondary Road Department, Linn County, Iowa)—Piloting a program to identify 1,000 miles of roadside for establishment and management of milkweed habitat. • Kayti Ewing (Botanist, Environmental Division, Arkansas DOT)—Maintains 1,000 miles of “Wildflower Routes,” consults with landowners to install pollinator habitat on adjacent roadsides through the Operation Wildflower program, and is working with District staff to identify areas where they can plant pollinator habitat and mow only once in the fall. Also working towards a CCAA with the USFWS. • Dan MacSwain (Natural Resources Coordinator, Washington County, Minnesota)— Negotiated a new rule to limit mowing/haying of roadsides in the county by adjacent land- owners. Consults with engineers on seed mixes and revegetation designs. 0% 5% 10% 15% 20% 25% 30% 35% 40% 3+/yr 1-2/yr Every 2-3 yrs Not needed Too variable Figure 39. Variety in answers regarding the frequency with which respondents mow the full width of the ROWs.

Product D: Best Management Strategies and Decision Support 69 • Stephanie Dobbs (Roadside Manager, Illinois DOT)—Implementing a reduced mowing program in roadside ROWs statewide. Planning to actively manage and monitor the center median of I-39 for monarch habitat to meet CCAA requirements. Findings Two distinct strategies were identified for installing and managing milkweed in roadside ROWs: • “Special Status” Areas—areas with unique conservation value are set aside and afforded special management, such as reduced mowing. – Arkansas DOT: Wildflower Routes and Operation Wildflower areas – Linn County, Iowa: 1,000 miles of milkweed pilot • Broad Management Prescriptions—new management regimes are adopted for entire road systems or components thereof to promote milkweed and pollinator habitat. – Illinois DOT: reduced mowing along I-39 center median – Washington County, Minnesota: new haying/mowing restrictions Findings included the following: • Almost every interviewee had conducted an inventory of roadsides at some point—some 30 years ago, some last year. In all but one case, the inventory was conducted via “window inventory” (i.e., from the vehicle). • Only one interviewee had conducted any quantitative monitoring (Stephanie Dobbs, ILDOT), However, Ms. Dobbs was very clear that she did not expect other roadside managers to do the same. Those who are participating in the energy and transportation CCAA do expect some monitoring requirement. • GIS-based data management is increasingly common. Most departments are porting their paper data to a GIS; however, most feel they are behind in the effort. In Minnesota, they have used the Collector app to inventory weeds; in Arkansas, crews have and use tablets in the field; in Illinois, the Collector app has also been used for a couple of applications. • Most interviewees had set targets in terms of milkweed plants/stems or wanted to know how many additional milkweed plants/stems resulted from changes to management. • Areas with “bare dirt opportunities” are the easiest to target for milkweed and forb seeding, which are more common in populous or economically developing areas. Prepping sites specifically for monarchs is time intensive and costly. Habitat Calculator—Use Scenarios The following capture how respondents indicated that they thought the Habitat Calculator could be used: • Identify roadside ROWs for which revegetation is already planned due to road work and which should include milkweed and nectar-producing forbs. • Identify currently vegetated roadside ROWs for creation or enhancement of monarch habitat. • Identify roadside ROWs to exclude from creation or enhancement of monarch habitat due to threats. • Estimate progress towards program goals (one milkweed per 11 ft of roadway) or compliance requirement (CCAA). • Inventory existing monarch habitat within road system.

70 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies Most Common Users The research team was able to profile two types of users for the Habitat Calculator: • Common: Individual or small team of DOT staff (e.g., any roadway authority, including state, county, or municipal) with a dedicated window of time (one to five days per year) to inventory and monitor potential or existing monarch habitats within the road system under their authority. – Roadside vegetation managers, – Biologists in environmental compliance departments, and – Natural resource program interns. • Less Common: roadside crew members on contract or under direct employment of a DOT during routine maintenance activities: – Mowing personnel. – Herbicide applicators. Decision-Support Tree At the first and second team meetings, the researchers built and refined a decision-support tree that represents decisions roadside managers often make. Below are simplified figures (Fig- ures 40, 41, and 42) that reference a more complex decision tree that is difficult to represent in print format. Also refer to Figure 5 (in Chapter 1 and Appendix A) that depicts a manager’s workflow in regard to decision making regarding ROWs conservation. Decision-Support Materials For each part of the decision trees, the researchers identified pertinent materials for the deci- sion. The team wanted information that could be easily accessible to a manager, something brief yet informative, and provided links to additional information if more detail was desired. On a website, links to appropriate existing materials can be made. For example, if considering mowing as a management practice, one can consult the Mowing and Management: Best Practices for Monarchs handout written by Monarch Joint Venture (https://monarchjointventure.org/images/ uploads/documents/MowingForMonarchs.pdf). In other cases, when the team discussed the topic, it could not identify existing material that would be useful. Those were topics that were prioritized for development within the team. Together, these will complement existing resources. The vision is to provide these materials via a website, but the team has not yet had the capacity to design the website. How are you considering enhancing the roadside for monarch habitat? Revegetation following construction See Tree B Managing existing roadside vegetation See Tree A Figure 40. General schematic of decision support: best management practices for monarchs.

Product D: Best Management Strategies and Decision Support 71 Does it provide continuous bloom throughout the growing season? Is it a diverse stand of mostly native plants? Add transplants or interseed areas with species that will fill in gaps in bloom and help provide continuously flowering resources for monarchs. Has the roadside been inventoried and has a management planbeen putin place? Are milkweeds present? Interseed milkweed species or add transplants to increase milkweed density. Conduct a field assessment and then develop a site-specific management plan to address any habitat. Control invasive species that are outcompeting natives and reducing floral diversity. Is the site dominated by invasive species? Could carefully timed mowing, herbicides, or brush control increase plant diversity? Implement a management plan to increase plant diversity. Maintain milkweed and plant diversity through ongoing maintenance. YES NO Figure 41. Decision-Support Tree A. Best management practices for monarchs: managing existing vegetation. Existing Resources Nectar Plant Guides There are many native species that can be planted on roadsides to support monarchs. The researchers have produced recognition guides that highlight the most common milkweed spe- cies along roadsides. The Xerces Society has also produced lists of monarch nectar plants for each region of the lower 48 states. These fact sheets are available at: http://xerces.org/monarch- nectar-plants. Additionally, the USDA’s Natural Resources Conservation Service (NRCS) has produced monarch nectar plant guides for five regions of the country (and many state NRCS offices have developed lists for their state). The five regional guides are available at: www.nrcs. usda.gov/wps/portal/nrcs/detail/national/plantsanimals/pollinate/?cid=nrcseprd402207

72 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies Locating Plant Materials • The Xerces Society’s Milkweed Seed Finder provides a search tool for locating commercially available native milkweed seed sources by species and state. Available at: http://xerces.org/ milkweed-seed-finder. • Monarch Watch’s (www.monarchwatch.org) Milkweed Market Vendors provides a map of native milkweed vendors across the country. • The Xerces Society’s Pollinator Resource Center provides region-specific information about native plant nurseries. Is there an opportunity to enhance the revegetation project to create habitat for monarchs? Revegetation goals include one or more of the following: erosion control, weed control, or wildlife protection. Consider prioritizing: • Areas where the GIS Prioritization Model indicates high quality habitat context. • Opportunities to increase habitat connectivity. • Areas where public or partners have interest. • Areas where the planting will be visible. • Areas where there will be educational value. YES NOT SURE Are invasives controlled prior to and during construction? Revegetation goals include landscaping or visual enhancement. Manage noxious and invasive species before revegetation. Include maintenance staff in the planning process. Determine the most appropriate time for planting for the project (spring or dormant season for seeds; spring or fall for transplants). Consider using establishment mowing in the first year,post-seeding or other weed control methods to help plants establish effectively. Install signage to inform the public. Communicate with the public about your agency’s efforts to help support monarchs. Design seed mix using eco- regional native plants to address revegetation goals, selecting nectar plants with sequential, overlapping bloom times throughout the growing season and including milkweed. Design landscape planting to address revegetation goals, prioritizing the use of native plants including milkweed, avoiding cultivars bred for showiness, and including shrubs that are nectar sources for monarchs. Figure 42. Decision-Support Tree B. Best management practices for monarchs: revegetation.

Product D: Best Management Strategies and Decision Support 73 Best Management Practices For detailed information on best management practices for monarchs and other pollinators on rights-of-way, consult: • The Federal Highway Administration’s Roadside Best Management Practices that Benefit Pollinators handbook: www.environment.fhwa.dot.gov/env_topics/ecosystems/Pollinators_ Roadsides/BMPs_pollinators_landscapes. • Additional guidance is found here: www.environment.fhwa.dot.gov/env_topics/ecosystems/ Pollinators_Roadsides/BMPs_pollinators_roadsides.aspx. Revegetation Guidance • Visit nativerevegetation.org to find: – Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat. This report offers an integrated approach to facilitate the successful establishment of native plants and pollinator habitats along roadsides and other areas of disturbance associated with road modifications. The report takes practitioners through a compre- hensive process of initiation, planning, implementation, monitoring, and operations and maintenance of a roadside revegetation project with native plants for creating pollinator habitats and describes adapting/improving processes for future projects. The compre- hensive 500+ page online report offers an integrated approach to facilitate the successful establishment of native plants and pollinator habitat along roadsides and other areas of disturbance associated with road modifications. A primer and resource library accompa- nies the report. Available at: www.nativerevegetation.org/learn/manual_2017. – Consult the Ecoregional Revegetation Assistant Tool, an online, map-based tool to help practitioners to select native plants suitable for revegetation of a site by using filters for needed plant attributes, including soil type, moisture needs, salt tolerance, and nectar plants for monarchs. www.nativerevegetation.org/era. Case Studies • Examples of State DOT practices that support pollinators and monarchs can be found through the Federal Highway Administration’s Environmental Toolkit for Pollinators: www.environment. fhwa.dot.gov/env_topics/ecosystems/pollinators.aspx. • Additional case studies have been collected on the Roadside Habitat for Monarchs web- page: https://monarchjointventure.org/our-work/projects/roadsides-as-habitat-for-monarch- butterflies. New Materials Developed Series of Frequently Asked Questions (FAQs): Roadside Habitat for Monarchs Based on a need identified from DOTs, the research team compiled a list of frequently asked questions (FAQs) and answers to explain how monarchs use roadsides. These science-based explanations can be used by DOTs when interacting with the public about roadside management or revegetation practices to support monarchs. The team intends these questions to be made available through the project’s website where they will be easily accessible and can be “living documents” that may be updated as more information becomes available.

74 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies Roadside Habitat for Monarchs Frequently Asked Questions: Monarchs and Roadsides Monarch Butterflies and Roadsides How does roadside vegetation support monarchs? Milkweed on roadsides is readily used by adult monarchs who seek out milkweed stems and leaves to lay their eggs on and the nectar on milkweed flowers. Monarch larvae, or caterpillars, eat the leaves of many different species of milkweeds that grow in roadside areas. Roadsides can also provide diverse nectar sources which fuel adult flight, breeding, migration, and overwintering. Sources: Kasten et al. 2016; Pitman et al. 2018. Which types of roadside vegetation support monarchs? Adult monarchs feed on nectar from a variety of blooming plants, including wildflowers and shrubs and monarch caterpillars consume milkweed. Roadsides with diverse, flowering vegetation provide habitat for monarchs during breeding and migration. For example, fall-blooming flowers can be especially important to migrating monarchs, which need large quantities of nectar to generate the fat reserves that enable them to complete their long-distance migration to overwintering grounds and survive winter. Sources: Cariveau et al. 2019; Western Monarch Milkweed Mapper 2019. Do monarchs reproduce on roadsides? Yes. Monarchs use milkweed on roadsides for reproduction—eggs, caterpillars, chrysalises, and adults are all observed. Studies and monitoring efforts in the Midwest, Southern Plains, West, and other areas have documented monarchs’ use of roadsides for reproduction. Sources: Mueller & Baum 2014; Kasten et al. 2016; Pitman et al. 2018; Western Monarch Milkweed Mapper 2019; Cariveau et al. 2019. Are there tools available for roadside managers to monitor milkweeds and/or monarchs on roadsides? Yes, a rapid field assessment for milkweeds can be found on the Roadside Habitat for Monarchs website: https://monarchjointventure.org/our-work/projects/roadsides-as-habitat-for-monarch-butterflies. Another option is the national Integrated Monarch Monitoring Program (https://monarchjointventure.org/IMMP), which compares monarch habitat and use across different land-use types, including roadsides. This program is more quantitative and may be more rigorous when comparing different habitat types or regions across time.

Product D: Best Management Strategies and Decision Support 75 Does roadside vegetation that supports monarch butterflies also support pollinators and other beneficial insects? Yes! Roadside vegetation that supports monarchs also supports a wide range of insects, including butterflies, bees, flies, wasps, beetles, and more. Roadsides with diverse, flowering vegetation can serve as foraging habitat, provide a place to breed, nest, or overwinter, and help pollinators and other insects to move through landscapes by linking fragmented habitats. Sources: Dirig and Cryan 1991; Munguira and Thomas 1992; Ries et al. 2001; Saarinen et al. 2005; Hopwood 2008; Schaffers et al. 2012. Does monarch-friendly roadside vegetation provide any advantages to adjacent landowners? Yes, habitat on roadsides can help maintain healthy ecosystems and provide ecological services, such as crop pollination or crop pest suppression. Habitat increases the diversity and stability of the pollinator community, and when on or near farms, habitat can improve pollination and increase crop yields. Roadside habitat also supports the beneficial insects that are predators of crop pests and contribute to natural pest control. In addition, roadside habitat can provide other ecological benefits that can translate to advantages to adjacent landowners, including reducing soil loss and water runoff, increasing water filtration and carbon sequestration, and supporting grassland birds. Sources: Mader et al. 2014; Morandin and Winston 2006; Morandin and Kremen 2013; Varchola and Dunn 1999; Losey and Vaughan 2006; Harrison 2014. Threats to Monarchs Associated with Roads Are monarchs killed by collisions with vehicles? Yes, like many other animals and pollinators, monarch butterflies are killed by vehicles on roads. Few studies have estimated monarch mortality due to vehicles, but those that have note that the greatest risk for monarch collisions is during fall migration. Researchers in Illinois estimated that up to 500,000 monarchs were killed during the fall migration in the state; researchers in Texas estimated 1-3 million monarchs killed during the fall migration. Other studies in Mexico have estimated millions of monarchs killed on roadsides as the population’s migration concentrates closer to the overwintering sites. However, roadsides are also very productive habitat for monarch reproduction and in many locations, the numbers of monarchs produced on roadsides likely outweighs the numbers killed by vehicles, though studies are needed on this topic. Additional surveys are also needed for estimating variation in monarch road mortality across seasons, and identifying and better understanding of potential roadkill hotspots. Sources: McKenna et al. 2001; Munoz et al. 2015; Kantola et al. 2019 If roadsides have higher quality monarch habitat, will that increase collisions of monarchs with cars? No studies have examined this with monarch butterflies specifically, but research involving other butterfly species suggests that more diverse roadside habitat and roadsides with less frequent mowing are associated with reduced butterfly mortality, perhaps because butterflies are better able to find resources within the roadside habitat and are less pressured to cross the road in search of additional habitat. This research suggests that, rather than luring butterflies to areas where they are killed by vehicles more frequently, roadsides with high-quality habitat actually reduces butterfly mortality compared with grassy, low diversity roadsides. Sources: Munguira and Thomas 1992; Ries et al. 2001; Skórka et al. 2013. Do vehicle collisions with monarch butterflies increase during migration, and is there any way to prevent roadkill? Data are limited, but it appears that more monarchs are killed due to vehicle collisions during fall migration compared to other parts of their migratory cycle. In Illinois, monarch mortality due to vehicles peaked during fall migration. In Texas, when monarchs funnel through the state on their

76 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies way to overwintering grounds in Mexico, researchers found hotspots of mortality due to vehicle collisions. Roadkill hotspots were in less densely populated areas and sites with a more arid climate. The researchers suggest that migrating monarchs may spend more time flying lower to the ground during the afternoon in desert areas to seek shelter from the heat and may need to search more for nectar sources. Similar results have been found from studies in northern Mexico. Potential mitigation strategies for reducing monarch roadkill on recurring hotspots in Texas and Mexico are under investigation. Sources: McKenna et al. 2001; Kantola et al. 2019. Does roadside runoff, including heavy metal deposition and road salt deposition, affect monarchs and milkweeds? Studies have shown that roadsides can suffer from heavy metal accumulation from car wear-and-tear and residual leaded gasoline emissions. In northern states, sodium from road salt application can accumulate along roadsides, and exhaust emissions can elevate levels of nitrogen. These chemicals can make their way into the leaves and nectar of plants growing next to the road. Studies to date suggest that toxic levels of metals, sodium, and other roadside pollutants are most worrisome along very high traffic volume roads, and just adjacent to the roadside. If we can prioritize restorations along low- or medium-traffic volume roads, and keep a mowed buffer adjacent to the roadside, we can likely avoid negative effects of roadside toxins on milkweed and monarchs. Sources: Snell-Rood et al. 2014; Snell-Rood in prep. Milkweeds on Roadsides What milkweeds are most common on roadsides? The answer to this question depends on what part of the country you are in. There are over 70 species of milkweeds native to the United States, but none of them occur in every state. To help roadside managers and others recognize milkweeds in their regions, we have developed milkweed recognition guides for 16 regions of the lower 48 states, found here: https://monarchjointventure.org/roadsidehabitat/bmp-support- materials. How do I know if there is milkweed on my roadsides? / How can roadside managers recognize milkweeds? We have created recognition guides to help you to recognize the milkweed species that are most common on roadsides in your area, found here: https://monarchjointventure.org/our-work/projects/roadsides-as- habitat-for-monarch-butterflies Most milkweeds have milky sap, so if you see a plant that looks like one of those in the guide to your region and milky sap oozes from the plant after breaking a leaf or stem, this is an indicator that you might be looking at a milkweed (though there are a few other types of plants, such as dogbane and spurges, which also have milky sap). Most milkweeds also have distinctive star shaped flowers that cluster together at the top of the plants. Then, when flowering is done, most milkweeds produce seed pods that open up to release brown seeds with white fluff attached (the fluff helps those seeds travel on the wind). There are a variety of factors (height, leaf shape, leaf arrangement, flower color, etc.) to help one distinguish among the different milkweed species—or even to recognize dried milkweed stems in the fall and winter. Additionally, some milkweed species are only found in certain soils. If you are seeking information beyond what is found in the recognition fact sheets, see Milkweeds: A Conservation Practitioner’s Guide (https://www.xerces.org/publications/guidelines/milkweeds-conservation-practitioners-guide) for more about milkweeds. Sources: Borders and Lee-Mader 2014 Are milkweeds in roadsides likely to spread to adjacent land and become weeds?

Product D: Best Management Strategies and Decision Support 77 Although milkweed, the common name for plants in the genus Asclepias, implies that the plants are indeed weeds, milkweeds are a diverse group of native wildflowers that are not listed as noxious weeds at either the state or the federal level in the United States. Milkweeds may have been perceived as weeds historically because a few species (out of the 70+ species in the U.S.) will readily colonize disturbed areas. These species tend to reproduce vegetatively (in addition to reproduction by seed), sending up new shoots from roots that spread outward from the parent plant. This clonal reproduction allows their populations to expand over time, and plants may spread out of their original area. Common milkweed (Asclepias syriaca) exhibits the highest degree of clonal reproduction, and vegetative growth also occurs to a lesser degree in horsetail milkweed (A. subverticillata), narrowleaf milkweed (A. fascicularis), plains milkweed (A. pumila), prairie milkweed (A. sullivantii), showy milkweed (A. speciosa), and whorled milkweed (A. verticillata). Despite the vegetative growth, many of these species are unlikely to create an ongoing and unmanageable weed problem for roadside managers (or adjacent landowners, other land managers, homeowners, etc.). Sources: Borders and Lee-Mader 2014. Are milkweeds in roadsides a concern for grazing animals on adjacent land? Milkweed species present in roadsides are unlikely to be a threat to livestock on adjacent property. Very few milkweed species will spread from their planting site. If milkweeds are present in pastures or rangelands, most livestock take care to avoid them. Although milkweeds are toxic, livestock generally find them highly unpalatable. Poisoning events are rare—but not unheard of—possibly because livestock must consume a large amount of milkweed to become sick or die. An average cow weighing roughly 1,200 lbs would need to eat 12 lbs or more (1-2% of their body weight) of dried milkweed on average to die. Milkweed poisoning typically only occurs when livestock are confined to a barren paddock with no alternate food sources or when hungry animals are released into milkweed patches. However, there are two species, western whorled milkweed (A. subverticillata) and narrowleaf milkweed (A. fascicularis) which have been reported as especially problematic for cattle and sheep, likely because of their growth forms and thin stems and leaves which are easily tangled in grasses and thus difficult for grazing animals to separate out. It is also important to note that the palatability of milkweed increases when it is dry. If adjacent landowners are haying the roadside, it is best to avoid haying areas where concentrations of milkweed are high. Sources: Panter et al. 2011; Burrows and Tyrl 2013 DiTomaso and Healy 2007; Schultz 2003; Malcolm 1991; Kingsbury 1964; Fleming 1920. Are milkweeds in roadsides that are hayed by adjacent landowners a risk to livestock? The palatability of milkweed increases when it is dry and so it is more likely that livestock will be sickened or even die from consuming dried milkweed in great enough quantities than fresh milkweed. If adjacent landowners are haying the roadside, it is best to avoid haying areas where concentrations of milkweed are high. However, large quantities of milkweed need to be ingested in order to cause harm. For example, an average cow weighing roughly 1,200 lbs would need to eat 12 lbs or more (1-2% of their body weight) of dried milkweed on average to die. The toxicity of milkweed varies by species and cardenolide concentrations (as well as local growing conditions); some species are generally of very low risk to livestock (e.g., butterfly milkweed, A. tuberosa) while others are consistently quite high (e.g., woollypod milkweed, A. eriocarpa). Sources: Burrows and Tyrl 2013; DiTomaso and Healy 2007; Schultz 2003; Malcolm 1991; Kingsbury 1964; Fleming 1920. How do milkweeds support pollinators or beneficial insects? Besides providing food for monarch caterpillars and adults, milkweeds support a wide range of pollinators and beneficial insect species. Milkweed flowers are a high-quality nectar source for pollinators such as bees, butterflies, wasps, beetles, flies, and more. Milkweeds also attract a wide range of insects that contribute to crop pest control, and some producers (e.g. vineyards in the Pacific Northwest) have begun to integrate milkweeds into their agricultural system in order to attract these important insects and support biological control. Milkweed leaves, stems, and roots support insect herbivores such as other lepidoptera

78 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies (butterfly and moth) species, wasps, flies, beetles, true bugs, and more. Milkweed “silk” (the fibers attached to the seeds and help the seeds catch the wind) can be used for nesting materials by vertebrates such as birds and small mammals. Sources: Tilman and Carpenter 2014; Borders and Lee-Mader 2014; James et al. 2016. What times of the year are milkweeds most readily observed in roadsides? In all of the lower 48 states, the majority of milkweed species will be observable during the growing season. The months during which you can most readily observe milkweeds depend somewhat on where you are. In much of the northern half of the country, the best months to see milkweeds on roadsides are from July to August. However, in Texas and southern Oklahoma, green antelopehorn and spider milkweed emerge in March, and are extremely important in that they help sustain the first generation of monarchs produced in the U.S. each year. Interestingly, in those two states, it can be difficult to find milkweeds in midsummer, as some of the most abundant milkweed species go dormant then; milkweeds can become abundant again in late summer or fall when conditions are more favorable. In the Desert Southwest, there are some native milkweeds that remain green during the late fall and winter. The same is true in the southeastern coastal plain with regards to a wetland species, aquatic milkweed (Asclepias perennis), which can be found along roadsides in winter in eastern TX (and presumably in other places along the Gulf Coast that have warm winters). How can roadside managers share information about the occurrence of milkweeds and monarchs in roadsides to improve understanding of habitat conservation? Set up a survey of monarch habitat and monarchs in your road system using the Roadside Habitat for Monarchs Rapid Assessment and Habitat Calculator (https://monarchjointventure.org/our- work/projects/roadsides-as-habitat-for-monarch-butterflies) and then share findings at statewide and regional meetings, such as the Rights-of-Way as Habitat Working Group meeting. Designate a staff member as point person for milkweeds and monarchs who can answer questions and be a liaison between roadside managers, administration, state monarch efforts, and conservation organizations. In your local, regional, or state jurisdiction, include milkweed and/or monarch sightings and location maps to the list of communications and reports that are shared among staff. Add milkweed and monarch sightings to community science portals: Journey North (all of U.S.; https://journeynorth.org) and/or the Western Monarch Milkweed Mapper (western U.S.; www.monarchmilkweedmapper.org/). Roadside Management for Monarchs How can roadside vegetation inventories benefit monarchs? A roadside vegetation inventory involves mapping the composition and condition of current roadside vegetation, including native, invasive, and noxious weeds. Such inventories can inform management plans that can benefit monarchs in a number of ways: Identification of remnant habitat can allow roadside managers to make informed decisions about how to manage remnant habitat to maintain and improve it, to help sensitive plant species survive and sustain habitat for monarchs and other wildlife.

Product D: Best Management Strategies and Decision Support 79 Roadside inventories can also be used to map out existing weed issues and identify emerging weed problems. Those data can then be used to help target management operations and to evaluate the effectiveness of weed management techniques. Inventories may be used to learn about the effects of management strategies across different management areas. Finally, inventories can help identify opportunities for future monarch-friendly revegetation efforts. How can a roadside manager assess the value of roadside vegetation for monarchs? A habitat assessment tool for monarchs can be found on the Roadside Habitat for Monarchs project website: https://monarchjointventure.org/our-work/projects/roadsides-as-habitat-for-monarch-butterflies How does roadside mowing impact monarch caterpillars and adults? Mowing during the growing season affects monarchs by removing nectar sources and reducing milkweed availability (but see milkweed stimulation question below), and can result in direct mortality of butterfly eggs, larvae, and sometimes adults. For these reasons, mowing can set back monarch breeding temporarily and can remove nectar sources needed during monarch migration. (In some regions, mowing can stimulate milkweed regrowth, and monarchs prefer to oviposit on mown milkweed when both mowed and unmowed plants are available; see “Could roadside mowing stimulate milkweed?” question below.) In general, it is preferable to mow when monarchs are not present; however, there may be circumstances when mowing when monarchs are present is more beneficial to the long-term quality of habitat for monarchs. See the Monarch Joint Venture handout “Mowing and Management: Best Practices for Monarchs” for more information, including management windows. Sources: Morris 2000; Johst et al. 2006; Noordijk et al. 2009; Kayser 2014, Thomas 1984; Wynhoff 1998; Humbert et al. 2010; Kayser 2014. When should roadsides be mowed to reduce impacts to monarchs? It is best to mow when monarchs are not present (see management window map below). Based on the best available data for when and where monarchs breed, Monarch Joint Venture and Xerces Society have developed regionally appropriate monarch breeding habitat management windows. These windows are periods when management activities are least likely to have negative effects on monarchs—especially immature monarchs. The exact timing of monarch breeding may vary from year to year and site to site (but try consulting a website such as JourneyNorth or Western Monarch Milkweed Mapper to see when monarchs are reported in your area)—and these windows may be revised in the future as we learn more. This is especially true for areas where few data are currently available on the timing of monarch breeding, such as the states that straddle the continental divide. Also, as long as milkweed is present in the landscape during the breeding season, there is a chance that monarchs are also there and that management actions could result in monarch mortality. As every year and site is slightly different, it is useful to survey milkweed plants for immature stages of monarchs prior to mowing. This is time consuming but is especially helpful if the management timing falls on the cusp of the recommended window for your region or if it has been an early spring/late fall year (see Figure 43). Could roadside mowing stimulate milkweed growth and support monarch breeding? Limited research in eastern North America has shown that spring or summer mowing can promote new growth and extend the availability of milkweed plants for monarch breeding. Mowing may stimulate growth of some milkweed species, particularly those that spread through rhizomes like common milkweed (A. syriaca) and showy milkweed (A. speciosa). Summer (June or July) mowing in Michigan resulted in more monarch eggs on regenerated stems than unmowed stems. Summer (July) mowing and burning can increase

80 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies Figure 43. Map depicting best time windows for management actions that may affect monarch breeding habitat (from the MJV, “Mowing and Management: Best Practices for Monarchs” handout). green antelopehorn milkweed (A. viridis) availability in the late summer and early fall in the Southern Great Plains, whereas in areas without mowing, the milkweed has senesced by August. In the West, showy milkweed will regrow after summer mowing and continue to support monarch breeding (Stephanie McKnight, personal observation). However, more research is needed in other areas to determine the optimal timing and frequency of mowing that promotes not only milkweed but also nectar plants. It is also unknown if the benefit of additional milkweed availability in the fall outweighs the costs of the larval mortality caused by summer mowing. The benefits are likely greater in areas that primarily have breeding monarchs in the spring and fall and where the dominant species of milkweed spread by rhizomes. Sources: Alcock et al. 2016; Baum and Mueller, 2015; Bhowick 1994; Haan and Landis 2019; Fischer et al. 2015. How does roadside mowing impact nectar plant abundance and diversity? Frequent roadside mowing beyond the safety zone can reduce native plant species diversity and abundance and may also favor the development of grasses over herbaceous plant species, which can indirectly affect monarchs and other pollinators. However, moderate mowing levels—such as twice per season or less (it varies by region)—have been shown by multiple studies to increase plant species diversity in grassland habitats. Other studies suggest that a single mowing during the growing season or in the fall is more beneficial for floral diversity compared to two or more mowings in a year. It should be cautioned that spring or summer mowing, while potentially beneficial to plant diversity in some locations, can lead to direct mortality of monarchs and other pollinators. However, there may be circumstances when mowing

Product D: Best Management Strategies and Decision Support 81 when monarchs are present is more beneficial to the long-term quality of habitat for monarchs. Sources: Parr and Way, 1988; Williams et al., 2007; Mader et al., 2011; Forman, 2003; Noordijk, et al. 2009; Entsminger et al., 2017; Valtonen et al., 2007. How does herbicide use on roadsides impact monarchs? Noxious and invasive weeds can degrade habitat for monarchs by displacing valuable nectar plants and milkweed. Herbicides are a tool employed by many transportation departments to control noxious and invasive weeds, encroaching woody vegetation, or vegetation that exceeds maximum height specifications in safety zones on roadsides. However, herbicide use can have non-target effects that reduce the quality of roadside habitat for monarchs by removing flowering plants and milkweed plants and may also have some direct negative impacts on pollinators themselves. Following best management practices for use of herbicides in relation to pollinators and other wildlife will assist managers in minimizing adverse effects on monarchs. A fact sheet on this topic summarizes recommended practices and can be found on the Roadside Habitat for Monarchs website: https://monarchjointventure.org/our-work/projects/roadsides-as- habitat-for-monarch-butterflies. Sources: Russell and Schultz 2010 Does reduced roadside mowing increase vehicle collisions with deer or other large mammals? Frequency of mowing of the entire roadside does not appear to influence rates of deer–vehicle crashes. In fact, deer may actually prefer some roadsides that are mowed more frequently because mowing can increase the palatability of some plants. A strip of vegetation adjacent to the pavement, often referred to as the clear or safety zone, that is mowed regularly, while allowing the rest of the roadside grow to a reasonable height, can help maintain visibility for drivers and prevent deer–vehicle crashes. Driver safety may increase with the presence of wildflowers and diverse vegetation by reducing monotony on roadsides, which improves driver awareness. Sources: Mastro et al. 2008; Barnum and Alt 2013; Guyton et al. 2014. Are there other advantages to reducing mowing and herbicide use beyond helping pollinators? Often there are cost savings associated with reduced mowing and efficient herbicide use. There are also many ecological benefits, including reduced carbon emissions, reduced herbicide runoff, and improved habitat for small wildlife such as grassland birds. Sources: Harrison 2014. What are some roadside mowing strategies that roadside managers have used to support monarchs? Illinois DOT has reduced mowing of roadsides beyond the 15’ safety zone in many areas, mowing different sections of the right-of-way once a growing season rather than mowing the entire right-of-way. Texas DOT manages rights-of-way for the protection of wildflowers and pollinators. Mowing operations start after the spring flowers have bloomed and set seed, usually around June. This is the best time for the mowing operation and by this time the monarchs are out of the state. Mowing at this time opens the canopy for warm-season species, and TxDOT sets all mowers to 7 inches to ensure less damage to warm-season plants. TxDOT also conducts a fall mowing operation that opens up the canopy so the cool season flowers have room to germinate and establish for the following year. TxDOT also sets aside as much right of way as possible in non-mowed areas. These areas are great for wildlife habitat and fall-blooming nectar plants such as Maximillian Sunflower, Goldenrod and Gayfeather. Case studies are available at the Federal Highway Administration’s Pollinators page in their Environmental Review Toolkit (Select the State DOT Pollinator-Friendly Practices and Information tab): www.environment.fhwa.dot.gov/env_topics/ecosystems/pollinators.aspx How do non-native and/or invasive plants in roadsides affect milkweeds and monarchs?

82 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies Invasive plants on roadsides can greatly reduce the abundance of milkweeds by outcompeting them for water, light, space, and nutrients, and thereby limit the reproductive potential of monarchs. Invasive plants can also outcompete the wildflowers that serve as nectar sources for monarch adults. By reducing the abundance and diversity of milkweeds and nectar sources, invasive plants reduce the food supply for adult monarchs, leading to reduced monarch abundance. How can the transfer of seeds on mowing equipment affect roadside habitat for monarchs? Mower decks (above and underneath), the area around the gear box, as well as blades and shafts can transfer the seeds of noxious and invasive weeds, species that can seriously degrade vegetation quality and diversity once they invade new sites. Adult monarchs rely on diverse sources of nectar throughout the breeding season as well as during migration. If invasive species become dominant, this can reduce the diversity of native plants available to provide nectar throughout the entire growing season. Preventing the spread of weed seed can help to reduce new invasions. How does haying of roadsides affect monarchs and milkweeds? Annual haying at the right time can benefit herbaceous roadside plant communities by suppressing the growth/encroachment of woody vegetation and reduce competition from tall grasses, allowing flowering plants to thrive. However, it can have negative effects on monarchs by abruptly removing milkweed and flowers at a site and destroying immobile eggs and larvae. To provide refuges for monarchs, harvest hay in strips or patches, instead of harvesting hay from an entire site. Cut hay at a high height (8–12”), so that some wildflowers can recover and go on to flower later in the season. Varying the season of haying from year to year may increase overall plant diversity. Sources: Feber et al. 1996, Foster et al. 2009. What impact does fire (either prescribed burns or wildfire) have on roadside monarchs and milkweeds? Prescribed fire is an important management tool; if carefully implemented, fire can be used to control unwanted woody vegetation and some invasive plants, stimulate wildflowers in fire-adapted plant communities, and reduce plant litter buildup that can suppress nectar resources for pollinators such as the monarch. The response of adult monarchs has been reported to be positively correlated with the post-fire availability of nectar resources, with significantly more monarchs using burned areas compared to unburned areas, especially during the first growing season after a fire. Burns (either prescribed or wild) during the growing season may stimulate growth of certain milkweeds, depending on the region (e.g. In Oklahoma, researchers found that summer prescribed fire stimulated resprouting of A. viridis). However, implementing fire during the monarch breeding season can directly kill monarch eggs, larvae, and pupae, and temporarily remove nectar and host plant resources for adult monarch butterflies. Adjusting the timing of prescribed fire to occur outside the monarch breeding and migration season can reduce the impacts to monarchs. Implementing fire in the early spring before monarchs arrive to a region, in late fall after monarch migration is complete, or in the winter will have the least direct impacts on the butterfly. However, in some regions and under some circumstances, the long-term benefits to vegetation management or plant diversity of using prescribed fire while monarchs are present may outweigh the short-term costs. Sources: Rudolph and Ely, 2006; Vogel et al., 2010; Baum and Sharber, 2012; Moranz et al., 2012. Revegetation What kinds of plants can be planted on roadsides to support monarchs? In each region, there are many native species that can be planted on roadsides to support monarchs. We have produced recognition guides that highlight the most common milkweed species along roadsides. The Xerces Society has also produced lists of monarch nectar plants for each region of the lower 48 states. These fact sheets are available at: https://xerces.org/monarch-nectar-plants

Product D: Best Management Strategies and Decision Support 83 The USDA’s Natural Resources Conservation Service (NRCS) has produced monarch nectar plant guides for 5 regions of the country (and many of the state NRCS offices have developed lists for their state). The five regional guides are available at: http://nrcs.usda.gov/wps/portal/nrcs/detail/national/plantsanimals/pollinate/?cid=nrcseprd402207 What plants do monarchs use as nectar sources? Documented nectar plants for monarchs are summarized in these regional lists (https://xerces.org/monarch-nectar-plants), but additional studies will likely increase our knowledge of the plants they use. Although they are known to nectar on a wide variety of plants (and thus are considered nectar plant generalists), there are many plant species that they rarely or never visit, and a smaller number of plant species that they strongly prefer. For example, many milkweed species, in addition to providing food for caterpillars, are also preferred nectar sources. Until we know more about monarch nectar preferences, you can refer to the regional monarch nectar plant lists that the Xerces Society in collaboration with Monarch Joint Venture or the NRCS has developed for each region of the lower 48 states. These plant lists are available at: https://xerces.org/monarch-nectar-plants www.nrcs.usda.gov/wps/portal/nrcs/detail/national/plantsanimals/pollinate/?cid=nrcseprd402207 www.calflora.org/app/ipl?list_id=px771&incvar=t When revegetating roadsides, how can planners consider the needs of monarchs? Include wildflowers or shrubs that are nectar sources for monarchs. Include species that bloom in spring, species that bloom in summer, and species that bloom in fall so nectar is available throughout monarch breeding and migration periods. Monarch nectar plant lists are available at: https://xerces.org/monarch- nectar-plants and www.nrcs.usda.gov/wps/portal/nrcs/detail/national/plantsanimals/pollinate/?cid= nrcseprd402207 Include native milkweed species in seed mixes or in landscape plantings. In regions where milkweed is difficult to establish from seed (e.g., California), using transplants may be a more cost effective way to establish milkweed in roadside habitat. For a directory of sources of milkweed seed, visit https://xerces.org/milkweed-seed-finder. What are some general guidelines for designing seed mixes or landscape plans for roadsides that can support monarchs? Include a diversity of plants; diverse communities are better able to prevent erosion, resist weeds, help with water infiltration, and are aesthetically pleasing. Include species that can fill different roles. Cool season grasses green up early in the spring and can provide erosion control from late winter into early summer, while warm-season grasses provide erosion control as they grow through the warm summer months and into the fall. Legumes can fix nitrogen and improve soil health. Annual forbs will establish quickly to provide attractive vegetative cover, erosion control, and nectar for monarchs during the time it takes for longer lived perennial forbs to establish. Avoid taller herbaceous plants in areas where lines of sight could be blocked, such as intersections and other safety zones. In areas with snow and ice, species to be planted close to the road should have some level of salt tolerance to reduce damage from road salt applications.

84 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies Include species adapted for the soil conditions present at the roadside site (e.g., use moisture- tolerating species for wet ditches), or, if seed mixes cannot be context-specific, include species adapted to a wide range of growing conditions. Focus on wildflowers that establish easily and are relatively inexpensive, but also include some species that are harder to establish and may be a bit more expensive to increase the aesthetics of the planting and the value of the habitat to monarchs. To achieve high plant diversity and long-term stability of a stand of vegetation intended for erosion control, a minimum of 25% of the seed mix should be wildflowers, but 50% results in a considerably more diverse planting. In highly visible areas, seed mixes for showy plantings should include greater than 50% wildflower component. Check erosion control mulches, seed laboratory reports, and legal seed labels of the planting stock. Mulches, seed, and other planting stock should be free of noxious weeds, invasive/introduced species, and other crop components. Where available and economical, native plants and seed should be procured from local ecotype providers. Local ecotype plant materials are adapted to the local climatic conditions and will generally establish well and will have bloom times in sync with the presence of monarchs and other pollinators. Some cultivars have been bred for a particular trait such as showiness and may have little to no pollen and nectar and therefore little value to monarchs. Sources: Lippit et al. 1994; Hopwood et al. 2015. Why use native plants in new roadside plantings, if they are more expensive than nonnative species? In addition to their value to pollinators, there are many advantages of using native plants to stabilize roadsides. Native grasses and flowers are best adapted to local growing conditions, require minimal inputs for establishment, and are able to tolerate extreme weather events such as drought. Native plants in roadsides are less likely than many nonnative plants to become weed issues and encroach on adjacent land. The root systems of native plants can increase water infiltration, which reduces runoff and water pollution and keeps our waters cleaner. A diverse native plant community can reduce soil erosion and resist weed invasions, which can reduce maintenance costs. Although native plants may cost more upfront, they can provide cost savings over time. Native plants can be aesthetically pleasing during the growing season while also acting as snow fences in the winter, trapping and preventing snow from blowing across roads. Roadsides with a diverse assemblage of plants sequester more carbon than weedy or species poor habitats. Native plant communities also support more birds, pollinators, and other wildlife. The use of native plants in roadsides can provide ecological benefits to the surrounding landscape. Sources: Cramer 1991; Bugg et al. 1997; Harper-Lore and Wilson 2000; Johnson 2000; Ries et al. 2001; Quales 2003; Blumenthal et al. 2005; Tilman et al. 2006; Tallamy and Shropshire 2009; Williams et al. 2011; Harrison 2014; Harper- Lore et al. 2014. What should planners consider when selecting sites for roadside plantings that support monarchs? When thinking about where to prioritize plantings that support monarchs, planners should consider the surrounding landscape, existing weed pressure, width of site, visibility to the public and potential for community engagement. Considerations include: Prioritize sites that are unlikely to undergo construction within 10-15 years following establishment of vegetation to ensure the long-term persistence of the plantings and to protect the investments of cost and time. Focus efforts on the widest roadsides to maximize potential habitat. Prioritize sites that connect other existing habitat within the landscape. Sites with high weed pressure may be challenging to return to native vegetation; DOTs that have limited experience with native plant revegetation may want to begin revegetation efforts on sites with low weed pressure.

Product D: Best Management Strategies and Decision Support 85 If a project goal is to highlight the value of DOT rights-of-way, sites planted with showy wildflowers to benefit monarchs and pollinators should be located in areas that are visible to the public, such as rest areas, or sites near farms that could benefit from the pollination services the roadside habitat would help to support (e.g., roadside sites near almond orchards in California). Public education and perception of the planting is important. Visible plantings may make surrounding landowners more aware of the importance of roadside habitat, which may decrease landowner spraying, mowing, or haying of the roadside. Signage can also be a valuable tool for educating community members. What kinds of tools are available to guide or inform decisions of planners? A habitat prioritization modelling tool and a decision tree is available through the Roadside Habitat for Monarchs project website: https://monarchjointventure.org/our-work/projects/roadsides-as-habitat-for- monarch-butterflies. Ecoregional Revegetation Assistant Tool A map-based tool to aid practitioners when selecting native plants for restoration and pollinator habitat enhancement. The map can be searched by U.S. Environmental Protection Agency (EPA) Level III Ecoregions, as well as by state. The database includes plant attributes such as soil type, moisture needs, palatability, salt tolerance, and value to pollinators, including nectar plants for monarchs. The plant species found within an ecoregion can be filtered by attributes, and a list of workhorse plant species can also be generated. This is part of a collaboration between the Federal Highway Administration, U.S. Forest Service, WSP, and Xerces Society. This tool can help practitioners to select native plants suitable for revegetation of a site by using filters for needed plant attributes, including value to pollinators. The tool is available at www.nativerevegetation.org/era. Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat This report offers an integrated approach to facilitate the successful establishment of native plants and pollinator habitats along roadsides and other areas of disturbance associated with road modifications. The report takes practitioners through a comprehensive process of initiation, planning, implementation, monitoring, and operations & maintenance of a roadside revegetation project with native plants for creating pollinator habitats, and describes adapting/improving processes for future projects. The comprehensive 500+ page online report offers an integrated approach to facilitate the successful establishment of native plants and pollinator habitat along roadsides and other areas of disturbance associated with road modifications. A primer and resource library accompanies the report. Available at: www.nativerevegetation.org/learn. Authors: Jennifer Hopwood, Emma Pelton, Ray Moranz, Stephanie McKnight, Stephanie Frischie (Xerces Society for Invertebrate Conservation) Acknowledgements: We thank the following reviewers for their input on this document: Wendy Caldwell (Monarch Joint Venture), Alison Cariveau (Monarch Joint Venture), Angela Laws (Xerces), Dennis Markwardt (Texas DOT), Dennis Martin (Oklahoma State University), Cora Lund Preston (Monarch Joint Venture).

86 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies References Alcock, John., Lincoln P. Brower, and Ernest H. Williams Jr. 2016. Monarch butterflies use regenerating milkweeds for reproduction in mowed hayfields in northern Virginia. The Journal of the Lepidopterists’ Society 70.3:177–181. Baum, K. A., and E. Mueller. 2015. Grassland and roadside management practices affect milkweed abundance and opportunities for monarch recruitment, pp 197–202. In Monarchs in a changing world: Biology and conservation of an iconic butterfly. (K. S. Oberhauser, K. R. Nail, and S. Altizer, eds.). Cornell University Press, Ithaca, New York (2015):197–206. Baum, Kristen A., and Wyatt V. Sharber. 2012. Fire creates host plant patches for monarch butterflies. Biology Letters 8.6:968–971. Barnum, S. A. and G. Alt. 2013. The effect of reduced roadside mowing on rate of deer-vehicle collisions. In Transportation Research Board 92nd Annual Meeting Compendium of Papers. https://pubsindex.trb.org/view/2013/C/1242942. Bhowmik, Prasanta C. 1994. Biology and control of Common milkweed Asclepias syriaca 327:227–250. Blumenthal, D. M., N. R. Jordan, and E. L. Svenson. 2005. Effects of prairie restoration on weed invasions. Agriculture, Ecosystems and Environment 107:221–230. Borders, B., and E. Lee-Mäder. 2014. Milkweeds: A Conservation Practitioner’s Guide. 146 pp. Portland, OR: The Xerces Society for Invertebrate Conservation. Bugg, R. L., C. S. Brown, and J. H. Anderson. 1997. Restoring native perennial grasses to rural roadsides in the Sacramento Valley of California: Establishment and evaluation. Restoration Ecology 5:214–228. Burrows, G. E. and R. J, Tyrl. 2013. “Table 9.2: Toxicity and cardenolide content of species of Asclepias.” Toxic Plants of North America, 2nd Ed. Wiley-Blackwell, 1390 pp. Cariveau, A. B., E. Anderson, K. Baum, J. Hopwood, E. Lonsdorf, C. Nootenboom, K. Tuerk, K. Oberhauser, E. Snell-Rood. 2019. Rapid assessment of roadsides as potential habitat for monarchs and other pollinators. Frontiers in Ecology and Evolution Volume 7, Article 386: https://doi.org/10.3389/fevo.2019.00386. Cramer, C. 1991. Tougher than weeds: native prairie plants, better management trim roadside spraying 90%. The New Farm 13:37–39. Dirig, R., and J. F. Cryan. 1991. The status of silvery blue subspecies (Glaucopsyche lygdamus lygdamus and G. L. couperi: Lycaenidae) in New York. Journal of the Lepidopterists’ Society 45(4):272–290. DiTomaso, Joseph M., and Evelyn A. Healy. 2007. Weeds of California and other western states. Vol. 3488. University of California Agriculture and Natural Resources Publications. Entsminger, Edward D., J. C. Jones, J. W. Guyton, B. K. Strickland, and B. D. Leopold. 2017. Evaluation of mowing frequency on right-of-way plant communities in Mississippi. Journal of Fish and Wildlife Management 8.1:125–139. Feber, R. E., H. Smith, and D. W. Macdonald. 1996. The effects on butterfly abundance of the management of uncropped edges of arable fields. Journal of Applied Ecology 33:1191–1205. Fischer, S. J., E. H. Williams, L. P. Brower, and P. A. Palmiotto. 2015. Enhancing monarch butterfly reproduction by mowing fields of common milkweed. American Midland Naturalist. 173:229–240. Fleming, Charles E. The Narrow-leaved Milkweed (asclepias Mexicana) and the Broad-leaved or Showy Milkweed (asclepias Speciosa): Plants Poisonous to Live Stock in Nevada. No. 99. University of Nevada, 1920. Forman, R. T. T., D. Sperling, J. A. Bissonette, A. P. Clevenger, C. D. Cutshall, V. H. Dale, L. Fahrig, R. France, C. R. Goldman, K. Heanue, J. A. Jones, F. J. Swanson, T. Turrentine, and T. C. Winter. 2003. Road Ecology: Science and Solutions. Washington, D.C.: Island Press. Foster, B. L., K. Kindscher, G. R. Houseman, and C. A. Murphy. 2009. Effects of hay management and native species sowing on grassland community structure, biomass, and restoration. Ecological Applications 19(7):1884–1896. Garibaldi, L. A., I. Steffan-Dewenter, C. Kremen, J. M. Morales, R. Bommarco, S. A. Cunningham, et al. 2011. Stability of pollination services decreases with isolation from natural areas despite honey bee visits. Ecology Letters 14(10):1062–1072. Guyton, J. W., Jones, J. C. and Entsminger, E. D. 2014. Alternative mowing regimes’ influence on native plants and deer. Mississippi Department of Transportation (MDOT), Jackson, MS.

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88 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies Morandin, L. A., and C. Kremen. 2013. Bee preference for native versus exotic plants in restored agricultural hedgerows. Restoration Ecology 21(1):26–32. Morandin, L. A., and M. L. Winston. 2006. Pollinators provide economic incentive to preserve natural land in agroecosystems. Agriculture, Ecosystems & Environment 116(3):289–292. Moranz R. A., D. M. Debinski, D. A. McGranahan, D. M. Engle, J. R. Miller. 2012. Untangling the effects of fire, grazing, and land-use legacies on grassland butterfly communities. Biodiversity and Conservation 21.11:2719–2746. Morris, Michael George. 2000. The effects of structure and its dynamics on the ecology and conservation of arthropods in British grasslands. Biological Conservation 95.2:129-142. Mueller, E. K. and K. A. Baum. 2014. Monarch-parasite interactions in managed and roadside prairies. Journal of Insect Conservation 18:847853. Munguira, M. L., and J. A. Thomas. 1992. Use of road verges by butterfly and burnet populations, and the effect of roads on adult dispersal and mortality. Journal of Applied Ecology 29:316–329. Munoz, P. T., F. P. Torres, and A. G. Megias. 2015. Effects of roads on insects: a review. Biodiversity and Conservation 24(3):659–682. Noordijk, J., K. Delille, A. P. Schaffers, and K. V. Sýkora. 2009. Optimizing grassland management for flower-visiting insects in roadside verges. Biological Conservation 142:2097–2103. Oberhauser, K., R. Nail, and S. M. Altizer, (eds.). Monarchs in a changing world: Biology and conservation of an iconic butterfly. Cornell University Press, Ithaca, New York Panter, K. E., M. H. Ralphs, J. A. Pfister, D. R. Gardner, B. L. Stegelmeier, S. T. Lee, K. D. Welch, B. T. Green, T. Z. Davis, and D. Cook. 2011. Plants poisonous to livestock in the Western States. U.S. Department of Agriculture. Agriculture Bulletin 415:13–5. Parr, T. W., and J. M. Way. 1988. Management of roadside vegetation: the long-term effects of cutting. Journal of Applied Ecology 25:1073–1087. Pitman, G. M., D. T. T. Flockhart, and D. R. Norris. 2018. Patterns and causes of oviposition in monarch butterflies: Implications for milkweed restoration. Biological Conservation 217: 54–65. Quales, W. 2003. Native plants and integrated roadside vegetation management. IPM Practitioner 25(3– 4):1–9. Ries, L., D. M. Debinski, and M. L. Wieland. 2001. Conservation value of roadside prairie restoration to butterfly communities. Conservation Biology 15:401–411. Rudolph, D. C., C. A. Ely, R. R. Schaefer, J. H. Williamson, R. E. Thill. 2006. Monarch (Danaus plexippus L. Nymphalidae) migration, nectar resources and fire regimes in the Ouachita Mountains of Arkansas. Journal of the Lepidopterists’ Society. 60 (3):165–170. Russell, C., and Schultz, C. B. 2010. Effects of grass-specific herbicides on butterflies: an experimental investigation to advance conservation efforts. Journal of Insect Conservation, 14(1), pp.53–63. Saarinen, K., A. Valtonen, J. Jantunen, and S. Saarnio. 2005. Butterflies and diurnal moths along road verges: Does road type affect diversity and abundance? Biological Conservation 123:403–412. Schaffers, A. P., I. P. Raemakers, and K. V. Sykora. 2012. Successful overwintering of arthropods in roadside verges. Journal of Insect Conservation 16(4):511–522. Schultz, Brad. 2003. Showy Milkweed Identification, Toxicity, and Control. University of Nevada-Reno Extension. https://www.unce.unr.edu/publications/files/nr/2003/FS0360.pdf. Skórka, P., M. Lenda, D. Moroń, K. Kalarus, and P. Tryjanowski. 2013. Factors affecting road mortality and the suitability of road verges for butterflies. Biological Conservation 159:148–157. Snell-Rood, E.C., A. Espeset, C. J. Boser, W. A. White, and R. Smykalski. 2014. Anthropogenic changes in sodium affect neural and muscle development in butterflies. Proceedings of the National Academy of Sciences, 111(28), pp.10221–10226. Tallamy, D. W., and K. J. Shropshire. 2009. Ranking lepidopteran use of native versus introduced plants. Conservation Biology 23(4):941–947. Thomas, J. A. 1984. Conservation of butterflies in temperate countries: past efforts and lessons for the future. Symposia of the Royal Entomological Society of London. Tillman, P. G., and J. E. Carpenter. 2014. Milkweed (Gentianales: Apocynaceae): A farmscape resource for increasing parasitism of stink bugs (Hemiptera: Pentatomidae) and providing nectar to insect pollinators and monarch butterflies. Environmental Entomology 43(2):370–376.

Product D: Best Management Strategies and Decision Support 89 Tilman, D., P. B. Reich, and J. M. H. Knops. 2006. Biodiversity and ecosystem stability in a decade-long grassland experiment. Nature 441:629–632. Valtonen, A., K. Saarinen, and J. Jantunen. 2007. Intersection reservations as habitats for meadow butterflies and diurnal moths: Guidelines for planning and management. Landscape and Urban Planning 79.3–4:201–209. Varchola, J. M. and Dunn, J. P. 1999. Changes in ground beetle (Coleoptera: Carabidae) assemblages in farming systems bordered by complex or simple roadside vegetation. Agriculture, Ecosystems & Environment 73(1):41–49. Vogel, J. A., R. R. Koford, and D. M. Debinski. 2010. Direct and indirect responses of tallgrass prairie butterflies to prescribed burning. Journal of Insect Conservation 14.6:663–677. Western Monarch Milkweed Mapper. 2019. The Xerces Society for Invertebrate Conservation. Available at: https://monarchmilkweedmapper.org. Williams, D. W., L. L. Jackson, and D. D. Smith. 2007. Effects of Frequent Mowing on Survival and Persistence of Forbs Seeded into a Species-Poor Grassland. Restoration Ecology 15(1): 24–33. Williams, N. M., D. Cariveau, R. Winfree, and C. Kremen. 2011. Bees in disturbed habitats use, but do not prefer, alien plants. Basic and Applied Ecology 12(4):332–341. Wynhoff, Irma. 1998. Lessons from the reintroduction of Maculinea teleius and M. nausithous in the Netherlands. Journal of Insect Conservation 2.1:47-57. Best Management Practice Guide: Herbicides, Weeds, and Monarchs This guide is intended to fill a gap that practitioners noted, an overview of the impacts of herbicides on monarchs and how herbicides can be used to improve monarch habitat on roadsides. Please see Appendix E for a formatted version.

90 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies Roadsides as Habitat for Monarchs Monarch Butterflies, Weeds, and Herbicides Monarch butterflies are in decline in North America, and restoring monarch habitat, including roadsides, is important to the species’ recovery1. Monarch caterpillars require milkweed (primarily in the genus Asclepias) to complete their development. A diversity of milkweed species are found on roadsides2,3, and monarchs lay their eggs readily on milkweed plants in roadsides4 and consume nectar from milkweed flowers. Roadsides provide more than just milkweed; they can also provide diverse nectar sources to feed adult monarchs and other pollinators. Nectar fuels adult monarchs in their breeding, migration, and overwintering. Adult monarchs feed on nectar from a variety of blooming plants, including wildflowers and shrubs, throughout the growing season. Spring flowers support monarchs as they leave their overwintering grounds to breed, and summer flowers support several generations of breeding monarchs. Fall-blooming flowers are also important, as monarchs migrating to overwintering grounds require lots of nectar to build fat reserves to support their long-distance flights and sustain them through the winter. Noxious and invasive weeds can degrade habitat for monarchs by displacing valuable nectar plants and milkweed. Herbicides are a tool employed by many transportation departments and other land managers to control noxious and invasive weeds or encroaching woody vegetation. However, some herbicide uses have non-target effects that reduce the quality of roadside habitat for monarchs by removing flowering plants and milkweed plants or reducing plant diversity over time. This guide highlights best management practices to reduce the impacts of herbicides on monarchs. Best Management Practices Roadside managers and other vegetation managers can reduce the impacts of herbicide use on monarch butterflies by: 1. using herbicides within an integrated approach that incorporates a range of methods to prevent and manage weeds and non-compatible vegetation, 2. limiting nonselective broadcast applications, which can damage host or nectar plants, 3. using herbicides as efficiently as possible to reduce the amount applied, 4. reducing off-site movement of herbicides, and

Product D: Best Management Strategies and Decision Support 91 5. limiting direct exposure of monarchs to herbicides when possible. Specific management practices to reduce risk to monarchs from herbicide applications include: Applicator Training Train staff and contractors to distinguish noxious and invasive weeds and encroaching woody vegetation from similar species to reduce unintended damage to nontarget plants. For instance, training may help crews to distinguish the invasive Canada thistle (Cirsium arvense) from the native tall thistle (Cirsium altissimum), an important fall-blooming native nectar plant for migrating monarchs in the central states. Train applicators in herbicide application techniques that reduce damage to nontarget plants. Create specifications that would hold contractors accountable to using proper techniques. Assessment Inventory roadside vegetation regularly to identify emerging noxious and invasive weed issues or encroaching woody vegetation. Early detection of weeds can result in improved control and may reduce the amount of herbicide needed overall. Document desirable plants that may be present, such as native nectar plants and milkweeds. Planning Use herbicides within an integrated vegetation management plan. Evaluate the range of management techniques (e.g., chemical, cultural, biological, physical, and mechanical) in order to select the most effective, feasible, and least harmful weed management method(s) that can increase or conserve the abundance and diversity of blooming plants. Prioritize selective herbicides—those formulated to control specific weeds or groups of weeds— whenever possible, to reduce damage to nontarget plants. If using nonselective herbicides—products that are broad-spectrum and kill or damage a wide range of plants—use direct or targeted application methods or apply when desirable plants are dormant. If possible, avoid applications when monarchs are present (Use on-site scouting as well as expected windows of monarch activity, found here: https://monarchjointventure.org/images/uploads/documents/MowingForMonarchs.pdf.). Coordinate spray operations with mowing crews to enhance weed control. For example, it may improve control to treat mature weeds when they are actively growing, shortly after mowing. Choose and calibrate equipment with drift management in mind. Use nozzles that produce larger droplets that are less likely to drift off target. Calibrate equipment regularly to avoid over-application. Select herbicides with low volatility when feasible to reduce the off-target movement of herbicide vapors. Do not apply herbicides when temperatures are high (see label for more information) or during temperature inversions, when herbicides are more likely to volatilize. Use appropriate drift control agents. Prioritize the use of formulations that are jointly terrestrial and aquatic-approved, and that have lower residual activity and shorter half-life, when possible, in order to minimize potential impacts on the environment following application. Select adjuvants—products added to a spray solution to enhance performance of post-emergence herbicides—that are terrestrial and aquatic-approved, and compatible with the selected herbicide formulation.

92 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies Always apply herbicides according to label directions and use the minimum application rate that will effectively control the weed. Apply herbicides at the stage of growth when the weed is most vulnerable and the application likely to be most successful. This will be the seedling or rosette stage for some weeds. Consider the mode of action of the herbicide and the application technique when determining timing of application. For example, when using a systemic herbicide, treat perennial weeds in the late summer and fall, when perennials begin to move sugars down to their roots, so that the herbicide will be translocated to vegetative reproductive structures where it will be most effective at controlling the plant. When possible, treat plants before they convert from vegetative phase to floral phase and bloom; this will reduce the weed seed bank (reservoir of weed seeds in the soil). If weeds are treated just before bloom or after seed set, their populations may persist in future years. Treatment of weeds during their vegetative phase also reduces exposure of adult monarchs to herbicides and adjuvants. Apply herbicide sprays when weather conditions will minimize drift. Avoid applications when wind speeds are greater than 10 mph. Avoid applications during a temperature inversion (when warmer air above traps cooler air near the ground); these conditions cause herbicides and other pesticides to linger in the air, where they can move long distances off site with any air movement. No wind or wind speed below 2 mph suggests a possible inversion. Make direct, selective applications to target plants to avoid weakening nontarget species. Target weeds or non-compatible species using spot treatment applications made with a backpack sprayer, weed wiper, or similar technology. Use highly targeted applications to cut stems, stumps, or underneath bark. Limit the use of broadcast treatments or pellet dispersal only for dense infestations of weeds or non-compatible vegetation, or for safety zone or guardrail treatments. Use an approved marker dye with spot treatments or cut stem/stump treatments to allow the applicator to know the target has already been treated and the extent of target coverage. Spray dyes reduce likelihood of an accidental retreatment or missing treatment of a target weed. Post-Treatment Keep records of locations where herbicides are applied. Records on the plants treated, application method, type, and amount of herbicides used, and dates of application can help to evaluate the effectiveness of treatments over time and can be useful when adjusting management decisions. Your state agency charged with education or regulation of pesticide use will have example application record keeping forms that can be used. Multiple seasons of herbicide applications or other weed control methods may be needed to fully control an invasive species. Follow label directions and standard practices when rinsing or cleaning spray equipment in between work sessions; incomplete removal of a prior herbicide mix can have detrimental impacts to the next treatment area. Rinse off, or otherwise clean mower decks (upper and undersides), deflectors, gear box housing, and mower blades and shafts, between sites to avoid transferring weed seeds. This is especially important after mowing an area known to contain noxious or invasive weed species. After treating a dense infestation, consider seeding or replanting the area if necessary (e.g. if the seed bank was depleted of desirable species). Plant with desirable, competitive native species to reduce the need to re-treat the area. Always make sure that seed and vegetative planting stock is free of weed species. After treatment, monitor resulting conditions and outcomes to evaluate the effectiveness of management practices on target plants and any effects on nontarget plants. If desired conditions were not produced or if site conditions change, adapt management practices accordingly. Herbicide Applications

Product D: Best Management Strategies and Decision Support 93 Use of noxious or invasive weeds by monarchs [sidebar] Adult monarchs feed on nectar from a variety of blooming plants, including some noxious weeds or invasive non-native plants (such as Canada thistle, Cirsium arvense). However, if invasive species become dominant, this can reduce the diversity of other plants available to provide nectar throughout the season. For example, if Canada thistle is the only flowering plant present in a stretch of roadside, monarchs will only have nectar available to them from that single species which blooms during a small portion of the growing season, rather than a diverse patch of vegetation that could provide nectar from spring through fall. Hence, managing invasive plants will generally increase the abundance and diversity of plants that support monarchs and pollinators throughout the growing season. In highly degraded landscapes where native nectar sources are scarce, the large-scale removal of the noxious or invasive species may cause a short-term reduction in nectar for monarchs. In these circumstances, reseed with native blooming plants that are attractive to monarchs, known to compete well with weeds, and bloom within the first few years of planting in your seed mix. In time, these species and other native perennial plants should deter recolonization of invasive plants and provide a haven for monarchs and pollinators. Toxicity of herbicides to monarchs [sidebar] Although herbicides are formulated to kill plants and do not target insects, recent research indicates that some herbicides may be toxic to butterflies, particularly when ingested by caterpillars eating treated plants. Often, the herbicides are not immediately lethal but still have negative effects such as reducing butterfly size, weight, development rates, and survival5, 6, 7, 8. These sub-lethal effects may reduce butterfly populations over time6. These studies did not focus on monarchs and further research into the effects of commonly used herbicides, tank mixes, surfactants and other inert ingredients in formulated products on monarchs is needed. Until more is known, we recommend a cautious approach when applying herbicides to milkweed where monarch caterpillars are present. Avoiding direct applications to milkweed plants when feasible, for example, can reduce direct herbicide exposure to monarchs. Authors Jennifer Hopwood, Emma Pelton (Xerces Society for Invertebrate Conservation), Alison Cariveau (MJV) Resources Monarch Joint Venture: Roadsides as Habitat for Monarchs: https://monarchjointventure.org/our- work/projects/roadsides-as-habitat-for-monarch-butterflies Xerces Society: Regional guides to monarch nectar plants: https://xerces.org/monarch-nectar- plants/ Federal Highway Administration: Environmental Toolkit Review: Pollinators: https://www.environment.fhwa.dot.gov/env_topics/ecosystems/pollinators.aspx

94 Evaluating the Suitability of Roadway Corridors for Use by Monarch Butterflies References 1. Thogmartin, W.E., López-Hoffman, L., Rohweder, J., Diffendorfer, J., Drum, R., Semmens, D., Black, S., Caldwell, I., Cotter, D., Drobney, P. and Jackson, L.L., 2017. Restoring monarch butterfly habitat in the Midwestern U.S.: ‘all hands on deck’. Environmental Research Letters, 12(7), p.074005. 2. Pleasants, J.M. and Oberhauser, K.S., 2013. Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population. Insect Conservation and Diversity, 6(2): 135-144. 3. Mueller, E.K. and Baum, K.A., 2014. Monarch–parasite interactions in managed and roadside prairies. Journal of Insect Conservation, 18(5): 847-853. 4. Kasten, K., Stenoien, C., Caldwell, W. and Oberhauser, K.S. 2016. Can roadside habitat lead monarchs on a route to recovery? Journal of Insect Conservation, 20(6): 1047-1057. 5. Russell, C. and Schultz, C.B., 2010. Effects of grass-specific herbicides on butterflies: an experimental investigation to advance conservation efforts. Journal of Insect Conservation, 14(1): 53-63. 6. Stark, J. D., Chen, X. D. and Johnson, C. S., 2012. Effects of herbicides on Behr's metalmark butterfly, a surrogate species for the endangered butterfly, Lange's metalmark. Environmental Pollution 164: 24- 27. 7. Bohnenblust, E., Egan, J.F., Mortensen, D. and Tooker, J. 2013. Direct and indirect effects of the synthetic-auxin herbicide dicamba on two lepidopteran species. Environmental Entomology, 42(3): 586- 594. 8. Schultz, C.B., Zemaitis, J.L., Thomas, C.C., Bowers, M.D. and Crone, E.E., 2016. Non-target effects of grass-specific herbicides differ among species, chemicals and host plants in Euphydryas butterflies. Journal of Insect Conservation, 20(5): 867-877. Acknowledgements: We thank Wendy Caldwell, Aimee Code, Aaron Feggestad, Dennis Martin, Dennis Markwardt, Stephanie McKnight, Ray Moranz, Lewis Payne, Cora Lund Preston, and Michael Retterer for their review of this document. This work was conducted in the National Cooperative Highway Research Program, which is administered by the Transportation Research Board of the National Academies of Sciences, Engineering, and Medicine.

Product D: Best Management Strategies and Decision Support 95 Regional Milkweed Identification Field Sheets A diversity of milkweed species can be found growing on roadsides. Milkweeds can occur within intact natural plant communities on roadsides and several species can also colonize highly disturbed roadsides. Vegetation management that allows milkweeds to persist can sup- port monarchs. These regional guides are intended to help roadside managers recognize the most common native species found on roadsides. Formatted to include photos of key features and county level distributions, these short recognition guides highlight the most common spe- cies on roadsides within the region. The research team created 16 regional roadside milkweed recognition fact sheets (found in Appendix F). • Milkweeds of Arkansas, Louisiana, & Mississippi • Milkweeds of Arizona & New Mexico • Milkweeds of California • Milkweeds of Colorado • Milkweeds of Florida • Milkweeds of the Great Lakes • Milkweeds of Iowa & Minnesota • Milkweeds of Idaho, Oregon & Washington • Milkweeds of Kansas & Missouri • Milkweeds of the Mid-Atlantic • Milkweeds of Montana & Wyoming • Milkweeds of Nebraska & The Dakotas • Milkweeds of Nevada & Utah • Milkweeds of the Northeast • Milkweeds of Oklahoma & Texas • Milkweeds of the Southeast Discussion Roadside managers are already responsible for maintaining vegetation along our road- ways. This vegetation serves many functions, but its value to pollinators is often not the first priority. With proper educational tools and training to support roadside maintenance deci- sions, there are opportunities to make adjustments from small tweaks in mowing timing or frequency to larger-scale restoration or planting initiatives. The various products that have been developed through this project help managers to identify the best areas for habitat proj- ects and to assess the conditions of those habitats for monarchs. To supplement these tools, the researchers sought to provide descriptive answers to commonly encountered questions, provide educational materials on different species of milkweeds and nectar resources, provide the potential impacts and best practices for herbicide use in roadside areas, and guide deci- sions through a series of simple questions. These tools provide a good start for promotion to DOTs throughout the United States and will inform future educational and decision-support tools that would benefit roadside managers. The research team intends to make these resources accessible through the project web page and to begin promoting them to a list of project contacts. Ultimately, having an easily accessible and navigable website to share these tools in various fashions will benefit the project greatly.