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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS PART THREE Research and Education in the Southern Region
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS This page in the original is blank.
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS 10 Southeastern Apple Integrated Pest Management Dan L. Horton, Douglas G. Pfeiffer, and Floyd F. Hendrix, Jr. Integrated pest management (IPM), in its commercially usable forms, is a synthesis of discrete management concepts. Sustainability is an inherent theme of pest management. Fruit crops, because of their high unit value and the demand for blemish-free products, are an especially challenging area for IPM research and implementation (National Research Council, 1989). Compromises between scientists from several disciplines focusing on growers' needs to manage pest populations in an optimum cropping system lead to good pest management. Successful pest management is also regionally adapted. It attempts to exploit any regional advantages while adopting and modifying the successful IPM practices of other regions as they are needed. Low-input sustainable agriculture (LISA) funding in 1988 linked complementary apple pest management programs in Virginia and Georgia. Funding enabled both states to broaden and accelerate their long-standing commitments to pest management. Virginia is an important apple-producing state, while Georgia is not a major apple producer. The two are, however, on either end of the primary southeastern apple belt, which follows the Appalachian Mountains and includes production areas in North Carolina, South Carolina, Tennessee, and Alabama. Pest management programs in both Virginia and Georgia have sought to provide good regionally adapted control (Taylor and Dobson, 1974). The authors of this chapter have tried to provide growers with dependable, low-risk, preventative spray guidelines and to emphasize regional pest biology and selective, well-timed pesticide use. Through the years, significant effort has been made to encourage growers to adopt a pest management mentality. This chapter provides an
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS overview of pest pressures and phenology with particular emphasis given to the differences between Georgia and Virginia. OVERVIEW OF SOUTHEASTERN ARTHROPOD PESTS AND DISEASES Pests and beneficial arthropod complexes do not differ greatly from the mountains of north Georgia through North Carolina and on into much of Virginia. The abundance and severity of certain arthropod pests do vary within the region, however. Southeastern arthropod seasonality and pest severity were thoroughly evaluated and summarized in a 5-year study by Shaffer and Rock (1983). Management programs in Virginia and Georgia attempt to control primary pests (those that incur high economic cost if uncontrolled) early in the growing season. Control of primary pests commonly begins with the use of dormant oil. Sampling to estimate the size of successful overwintering populations of these pests is not feasible. Control of mites and aphids becomes more challenging, more disruptive to predators and parasites, and more expensive as the crop progresses beyond the 0.5-inch green-tip stage of development. Use of superior oil treatment gives nondisruptive suppression of scales, primarily San Jose scale (Quadraspidiotus perniciosus Comstock), European red mite (Panonychus ulmi Koch), and a complex of aphids, with the rosy apple aphid (Dysaphis plantaginea Passerini) being of primary concern. The delayed dormant period around the 0.25-inch green-tip stage presents a second and somewhat more effective control window for the use of oil. The addition of an organophosphate insecticide such as chlorpyriphos (Lorsban) in this oil spray for the green-tip stage improves the control of rosy apple aphid, which is not controlled by oil alone (Hull and Starner, 1983b). Tarnished plant bugs (Lygus lineolaris Palisot de Beauvois), spotted tentiform leafminers (Phyllonorycter blancardella F.), and green fruitworms (Lithophane antennata W. spp.) are injurious between the tight cluster and pink stages. Spotted tentiform leafminers are relatively new apple pests in the southeastern United States. Walgenbach et al. (1990) found that vigorous, prebloom control of overwintered leafminers generally provides acceptable season-long suppression. This minimizes the need for postbloom control, which often encourages mite outbreaks. Plant bugs are erratic, very mobile, and potentially damaging. The need for leafminer sprays at this stage makes integration of plant bug thresholds (Michaud et al., 1989) impractical for Georgia and Virginia growers since leafminer sprays provide plant bug control. Green fruitworms also are controlled at the pink and petal fall stages with sprays made for other pests. Prolonged cool springs with longer than normal periods between sprayings for the pink and petal fall stages
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS make a scheduled spraying at the pink stage very worthwhile in current IPM practices. The most important postbloom pests are codling moth (Cydia pomonella L.) and plum curculio (Conotrachelus nenuphar Herbst). Both of these primary pests attack the fruit. They are joined by tufted apple budmoth (Platynota idaeusalis Walker) and, in Virginia, variegated leafroller (Platynota flavendana Clemens) as pests that must be controlled for the production of a successful crop. San Jose scale crawlers, white apple leafhoppers (Typhlocyba pomaria McAtee), Japanese beetles (Popillia japonica Newman), green June beetles (Cotinis nitida L.), and European red mites must also be monitored and controlled as necessary. San Jose scale crawlers remain in the susceptible crawler stage of development for a very brief period. Emergence normally occurs at about the time of the second cover spray; however, more precise timing can be had by using the earliest pheromone trap catches as a biological fix to better predict crawler emergence (Pfeiffer, 1985). Japanese beetles and green June beetles may be injurious, and caution should be exercised. Spraying for foliage feeding by these pests is sometimes warranted, but control of these pests carries the risk of inducing mite problems. White apple leafhopper infestations also raise concerns over mite infestations. They carry a greater risk of inducing mite outbreaks because the carbamate insecticides (carbaryl, Sevin; formetanate hydrochloride, Carzol) needed to control them are especially toxic to mite predators (Rajotte, 1988). European red mites are challenging pernicious pests (Prokopy et al., 1980) whose leaf-feeding injury accumulates through a growing season. Mite management includes suppression with oil treatments early in the season. Conservation of natural enemies, primarily Stethorus punctum LeConte lady beetles and the predator mite Amblyseius fallacis Garman in the southeast (Farrier et al., 1980), is fostered by making every effort to avoid unnecessary pesticide use. Careful pest management minimizes all unwarranted pesticide use (Croft and Brown, 1975). This preserves mite predators and normally lowers pesticide inputs. Mite control decisions are based on regular monitoring and the use of thresholds. Apple diseases in Georgia are unique compared with those in much of the rest of the United States. Scab is a minor problem, while the summer rots are of major importance. The opposite is true from the mountains of North Carolina through the northeastern United States. A thorough investigation and understanding of the epidemiology of Georgia apple diseases was a necessary prerequisite to beginning a LISA program for the crop in Georgia. Black rot of apples in Georgia, caused by Botryosphaeria obtusa (Schw.) Shoemake, differs from the disease of northern areas in that conidia are the
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS primary source of inoculum. Infestation of buds occurs in the winter, infection occurs in the early spring, and the disease can cause losses in excess of 50 percent. Conidia of B. obtusa are produced on dead wood in the trees and on the orchard floor throughout the year (Beisel et al., 1984). Conidia are found on and in buds from December through March. Even though conidia of the fungus are present in the buds for several months, infection does not occur until the silver-tip stage of bud phenology. Thus, a single spray at the silver-tip stage instead of the five sprays suggested previously (Smith and Hendrix, 1984) can be used to control this fungus. The fungus does not rot fruit until about 6 weeks before harvest, even though infection occurs in March and April. Apple scab, which is caused by Venturia inequalis (Cke.) Wint., is a minor problem in Georgia because high temperatures frequently preclude secondary disease cycles. In most years, there is a primary cycle early in the spring. In some years, there is one secondary cycle in the fall (Hendrix et al., 1978). If an orchard had scab in the previous year, it is suggested that three scab sprayings be applied. In the absence of scab the previous year, no sprays are needed. Cedar apple rust (Gymnosporangium junipera-virginianae Schw.) and quince rust (Gymnosporangium clavipes Cke. & Pk.) occur to some extent in Georgia orchards (Hendrix et al., 1978). Two prebloom sprays are suggested for orchards where there is a history of a problem with these diseases, but no sprays are suggested in other orchards. Fire blight of apples (Erwinia amylovora [Burr.] Winslow et al.) occurs sporadically in Georgia apple orchards (Hendrix, 1990). Temperatures between 70° and 80°F and rainy, humid weather are necessary for epidemic outbreaks (Van Der Zwet and Keil, 1979). Avoidance of excessive vegetative growth also aids in disease reduction. Fire blight control by spraying is suggested only in those years when the weather favors major outbreaks. Brooks spot of apple (Mycosphaerella pomi [Pass.] Lindau) is a minor disease in Georgia. Light infection may not be noticed at the time of harvest because of the small lesion size. Infection occurs from late April to mid-June in North Carolina, but it is slightly earlier in Georgia because of warmer temperatures. Sprayings from the time of petal fall until the second cover appears to provide adequate control (Sutton et al., 1987). No sprays are suggested for use in orchards with no history of the disease. Black pox of apple (Helminthosporium papulosum Berg) can cause severe losses. The fungus reproduces in old bark lesions and spreads to new leaves, fruit, and bark. Infections occur throughout the growing season (Taylor, 1970). Because of the length of the period when infection can occur, orchards with a history of this disease require season-long preventative spraying and are not candidates for inclusion in a LISA-type program. Bitter rot of apple (Glomerella cingulata [Stonem.] Spauld. & Schrenk.)
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS does not reach damaging levels every year in Georgia orchards. When it does occur, it can cause losses of up to 80 percent (Noe and Starkey, 1980, 1982; Taylor, 1971). While infection can occur anytime after bloom, it is considered a midsummer disease. Most infections occur after the fruit reaches full size (Hendrix et al., 1978). Temperatures of greater than 21°C and free moisture are necessary for disease development. The fungus over-winters primarily on dead wood in the tree and on the orchard floor. It also survives on a small percentage of mummified Georgia fruit. The Georgia spray guide suggests five to eight sprays for pest control from the time of bloom to harvest. White rot on fruit and Bot canker on trees are caused by Botryosphaeria dothidea (Moug. ex. Fr.) Ces. & de Not. The fungus survives on dead wood in the tree and on the orchard floor. Conidia are produced throughout the summer, but fruit is susceptible to infection only after the soluble solids reach 10.5 percent (Kohn and Hendrix, 1982, 1983). This is usually about 6 weeks before harvest. Prior to the work of Kohn and Hendrix (1982, 1983), sprays were applied from the time of bloom to harvest. Botryosphaeria dothidea infects apple stems primarily through improperly made pruning cuts (Brown and Hendrix, 1981). Stub cuts on which the bark dies are the most common point of infection. This disease can be controlled by making proper pruning cuts and maintaining proper sanitation. Sooty blotch, which is caused by Gloeodes pomigena (Schw.) Copby, and flyspeck, which is caused by Zygophiala jamaicensis Mason, are fungi which grow on the surface of apples. They do not cause decay but do cause cosmetic blemishes. Efforts were made in 1986 and 1987 to monitor the development of these diseases and to control them with prescription-type sprays. None of the currently registered fungicides, however, is capable of arresting development of these diseases once they start. Control of sooty blotch and flyspeck in the orchard does not fit into any current IPM techniques for apple production. Data are not available for predicting these diseases. PATHOLOGY RESEARCH University of Georgia LISA fruit research centered on the development of IPM-compatible controls for sooty blotch and fly speck. The heavy preventative spraying required to control these diseases was not conducive to further pest management implementation. This study is examining the efficacy of chlorine dips for postharvest removal of sooty blotch and flyspeck from apples. The removal of pesticide residues and effects on shelf life were also examined.
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS TABLE 10-1 Chlorine Removal of Sooty Blotch and Flyspeck from Apples with a 5-Minute Postharvest Chlorine Dip Chlorine (ppm) Percentage Posttreatment Sooty Blotch Flyspeck 0 100a 100a 100 97a 96a 300 16b 70b 500 6b 56c NOTE: Fruits were not brushed. Values with the same symbol are not significantly different. Postharvest Removal of Sooty Blotch and Flyspeck Initial testing of postharvest chlorine dips in 1988 showed that these treatments removed sooty blotch and reduced flyspeck. Several postharvest chlorine rinses are labeled for use on a variety of fruits and vegetables. Sodium hypochlorite, the active ingredient, volatilzes rapidly, eliminating chlorine residues. The U.S. Environmental Protection Agency (EPA) has exempted sodium hypochlorite from food tolerances, indicating its low risk. The rates found to be effective are above those currently listed by the EPA. High levels of chlorine (940, 1,270, and 1,670 ppm) were found to remove completely sooty blotch from fruit at all concentrations tested. Flyspeck was reduced but not eliminated. This experiment was repeated with lower concentrations of chlorine (Table 10-1). At 300 and 500 ppm of chlorine, sooty blotch was reduced from 100 percent to 16 and 6 percent, respectively. Flyspeck was reduced from 100 percent to 70 and 56 percent, respectively. Fruit tested in both experiments showed no symptoms of phytotoxicity or damage to their finishes. This test was repeated five times, with similar results obtained each time. In subsequent tests, fruit was treated in the dump tank of a commercial packing plant. Fruit was exposed to 0, 50, 100, 300, 400, or 500 ppm of chlorine for 5 to 7 minutes. It was then passed over a series of wet brushes and rinsed with nonchlorinated water. The addition of brushes improved the process. Sooty blotch removal by treatment with 200 ppm of chlorine (Table 10-2) was equivalent to that at 500 ppm without brushing (Table 10-1). Flyspeck removal by treatment with 300 ppm of chlorine with brushing was equivalent to that with 500 ppm without brushes. With 500 ppm of chlorine and brushes, flyspeck was reduced from 100 to 27 percent. At
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS TABLE 10-2 Chlorine Removal of Sooty Blotch and Flyspeck from Apples in a Commercial Packing Plant Chlorine (ppm) Percentage Posttreatment Sooty Blotch Flyspeck 0 100a 100a 50 92b 95a 100 26c 45c 200 6d 52b 300 4d 58b 400 2d 36c 500 0d 27d NOTE: Fruits were dipped postharvest in chlorine-treated, dump tank water for 5 minutes, brushed, and then rinsed with nonchlorinated water. Values with the same symbol are not statistically significant. this level of chlorine, sooty blotch was reduced to 0 percent. This test was repeated in 1989 with similar results. Chlorine Treatment Effects on Pesticide Residues Sample apples that were treated with 500 ppm of chlorine, brushed, and rinsed in nonchlorinated water were tested for pesticide residue in an EPA-approved laboratory at the University of Georgia. Pesticide residues were reduced by the postharvest chlorine treatment (Table 10-3). Captan resi TABLE 10-3 Effects of a 5-Minute Dip of 500 ppm of Chlorine Followed by Brushing and Rinsing with Non-chlorinated Water on Residues of Captan, Phosmet, and Maneb on Harvested Apples Residues (ppm) Phosmet Treatment Captan Sample 1 Sample 2 Maneb Water dip 0.42 0.30 0.16 5.84 Chlorine dip 0.00 0.20 0.00 1.63 NOTE: Values are averages of 21 residue analyses.
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS TABLE 10-4 Effect of Postharvest Chlorine Treatment and Fruit Waxing on Weight Loss of Red and Golden Delicious Apples after 12 Weeks of Storage at 1° to 3°C Date 1 Date 6 Weight Loss (g) Treatment Weight (g) Standard Deviation (g) Weight (g) Standard Deviation (g) Cultivar Wax Chlorine Golden − + 105.9 10.4 101.2 10.3 4.7 Delicious + + 102.1 11.1 97.8 10.8 4.2 − − 97.4 7.6 92.6 7.5 4.8 + − 102.4 10.8 98.3 10.4 4.1 Red − + 154.9 16.5 150.7 16.0 4.2 Delicious + + 142.1 27.2 138.5 24.4 3.6 − − 156.1 15.7 152.0 15.3 4.1 + − 164.9 14.1 156.5 14.2 8.4 dues were reduced to less than detectable levels, phosmet levels were reduced by 33 percent or more, and Maneb levels were reduced by 73 percent. Shelf Life of Chlorine-Treated Apples Red Delicious and Golden Delicious apples were harvested and treated with chlorine in a commercial packing plant, and half of the fruit was waxed. The fruit was stored in boxes with dividers at 34° to 37°F for 12 weeks. Weight loss was determined by weighing individual fruit at 2-week intervals. Weight loss averaged about 4.5 percent for Golden Delicious and 3.6 percent for Red Delicious apples over the 12-week period (Table 10-4). Neither chlorine nor wax treatment affected weight loss. Phytotoxicity and Fruit Finish Trial Fruit was treated with chlorine at levels of up to 4,100 ppm, with and without buffer, to determine phytotoxic levels. Fruit finish was not affected at 4,100 ppm of chlorine, with or without buffer, even when fruit was stored for 30 days in plastic bags in the presence of chlorine solution. Conclusions of Fruit IPM Research Postharvest chlorine dips have been found to be an effective technique for the removal of sooty blotch and the reduction of flyspeck. Chlorine treatments allow growers to ignore sooty blotch and flyspeck. Postharvest use of chlorine complements existing IPM techniques, including sanitation;
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS scouting for insects, mites, and bitter rot; and prescription use of white rot control measures, as dictated by fruit-soluble solids and weather. A state label granting Georgia growers the right to elevate their chloride concentrations to 500 ppm has been obtained. Postharvest chlorine treatment has allowed Georgia growers to eliminate up to eight sprays that, in preventative programs, are dedicated, at least in part, to the control of sooty blotch and flyspeck. No chlorine treatment-induced phytotoxicity was observed, even when eight times the necessary concentrations or two times the necessary exposure durations were used. Apples can be stored for up to 3 months after treatment with minimal but acceptable weight loss. Postharvest chlorine treatment also reduces pesticide residues. This may be important, because many consumers feel that even minimal pesticide residues compromise food safety. ENTOMOLOGY RESEARCH Virginia Polytechnic Institute and State University (VPI&SU) has provided the research lead in entomology. Objectives are (1) pheromone mating disruption to control codling moth and variegated leafroller, (2) inventory of orchard ground cover management practices and evaluation of the impacts of these practices on mites, (3) determination of the toxicity of herbicides to the predaceous mite A. fallacis, and (4) assessment of grower IPM expertise. Mating Disruption Mating pheromones are chemical cues that many insects use to help them find mates. Pheromone mating disruption provides insect control without the use of conventional toxic insecticides. Saturation of an orchard with pheromone confuses the mate-finding process, which prevents mating and eliminates the damaging larval stages of these pests. The elimination or drastic reduction of reliance on conventional disruptive, toxic sprays to control these pests does a great deal to conserve natural enemies. This use of nondisruptive, behavior-altering chemicals may well usher in what has been called “second-stage IPM ” (Prokopy, 1987). Codling moth, a primary pest of apples, must be controlled each year. This entails considerable pesticide use. Rothschild (1982) reviewed codling moth biology and ecology and noted the characteristics of this moth that make it a good candidate for disruption of the mating process. The codling moth's narrow host range and relatively low fecundity, the females' limited dispersal capabilities, the low number of generations, and the apparent lack of nonolfactory mate-finding mechanisms were noted as factors that lend themselves to pheromonal control. Charmillot and Bloesch (1987) reported
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS through a drip line (every 21 days from February to May) at 15 lbs of N/ acre per application. Weeds were controlled manually after ratings of weed density were taken. In the spring, soil samples were taken to evaluate nematode populations, and roots were examined for root-knot nematode infestations. Soil temperatures were monitored by placing thermocouples at soil depths of 4 and 8 inches. For the 1989–1990 season, whole-plot soil treatments were expanded to include legume cover crops or manure combinations. Split plots were fumigated, solarized, or left untreated. Strawberries were planted in September. To date, only data on nematode populations and plant vigor ratings have been collected for these plots. Because of differences in climate and growing conditions, a different experimental protocol was used in Lubbock. Plots were established in the fall of 1988 in west Texas by using a randomized complete block design with four replications. The experimental variables were factorial combinations of bed height (20 or 40 inches) and soil treatment (untreated, 1 month of solarization under clear plastic, metam sodium fumigation with water incorporation). Nematode populations were sampled before and after soil treatment. All plants were killed by cold temperatures in December. In the Poplarville experiment, yet another protocol was required. Before the evaluation of solarization effects, Iron and Clay cowpeas were planted as a cover crop during the summer of 1988 and were tilled in the fall. Soil treatments were applied on September 1 and replicated six times. These treatments consisted of (1) clear plastic solarization for 2 months on raised beds, (2) clear plastic solarization on flat beds, (3) black plastic solarization on raised beds, (4) methyl bromide fumigation, or (5) an untreated control. On November 11, treatment plastic was removed, the plots were mulched with black plastic, and 12 Chandler strawberries were planted in each experimental unit. Strawberry yield and weed populations were evaluated in the spring. The following protocol was used in Overton to study the impacts of various treatments on soil chemistry. To evaluate the effects of soil solarization and manures with variable carbon (C)/N ratios on nutrient availability, studies were initiated in the summer of 1989 on a fine sandy loam soil. The experimental design was a split plot, with whole-plot treatments being solarized or unsolarized soil. The split-plot treatments were factorial combinations of poultry manure applied at a rate to give 500 or 1,000 lbs of N/acre equivalents (5 or 10 tons/acre of manure) and fresh pine sawdust applied at 0, 40, or 80 tons/acre. Control plots that were either unamended or received fertilizer with N, P, and K (250, 40, and 75 lbs/acre, respectively) were included as split treatments. Split-plot treatments were applied in July and tilled into the top 10 inches of soil. A clear plastic tarp (thick-
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS ness, 0.0015-inch) was applied from July 18 to September 26. Following solarization, soil samples were collected to a 6-inch depth. Suction lysimeters were placed at a depth of 16 inches in four of the split-plot treatments. Elbon rye was seeded as an indicator crop. Soil leachate was collected after each rainfall of greater than 2 inches. Chemical analyses of soil samples were conducted according to the testing procedures of Texas A&M University (College Station, Texas). Weed populations were evaluated during December. Results Soil Temperatures The mean maximum soil temperatures at the 4-inch depth in the center of the 8-inch-high bed were 113° and 105°F for solarized and nonsolarized soils, respectively. The total time above 104°F in 1988 at 4- and 8-inch depths for the 8-inch solarized bed was approximately 590 and 300 hours, respectively. For nonsolarized soil, these values were 74 and 0 hours at 4- and 8-inch depths, respectively. Yield At Overton, the total yield from solarized soil was greater than that from untreated soil in all years (Table 12-7). The yield was higher with fumigated soil than with solarized soil in 1988, but there was no difference between fumigated and solarized plots in 1989. Plants grown on 13-inch beds tended to have a greater total yield than did those grown on 8-inch TABLE 12-7 Effect of Soil Treatment on Strawberry Yield and Weed Control Total Strawberry Yield (lbs/acre) Surface Area Covered by Weeds (%) 5/30/88 Treatment 1988 1989 Yellow Nutsedge Annual Dicots* Number of Annual Weeds/Plot 3/15/89 Yellow Nutsedge Plants/Plot 6/24/89 Fumigation 17,329a† 21,991a 0.5a 0.8a 8a 4a Solarization 15,526b 20,628a 10.5b 2.6a 11ab 17b Bare soil 11,436c 18,428b 13.3b 8.3b 14b 13b * Weeds included Lamium amplexicaule L., Oenothera laciniata Hill, and Vicia dasycarpa. † Different letters indicate separation of means within columns by Duncan's test at the 0.05 percent level.
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS TABLE 12-8 Solarization and Manure Effect on Weed Populations at Overton in 1989 Number of Weed Seedlings/8 inches2 Treatment Purple Nut Sedge Dandelion Total Dicots Total Monocots Total Number of Weeds Solarization + manure 3 1 3 4 7 Solarization + no manure 9 4 12 11 23 No solarization + manure 29 15 19 29 48 No solarization + no manure 42 29 39 42 81 ANOVA* Solarization 0.01† 0.05 0.05 0.05 0.02 Manure 0.05 0.003 0.002 0.05 0.004 Solarization by manure interaction NS‡ 0.09 NS NS NS * ANOVA, analysis of variance. † Probablility of significance. ‡ NS, not significant. beds (data not shown). Because of record freezing temperatures in February 1989, the entire crop at Lubbock was lost. At Poplarville, soil treatments had no effect on the yields (data not shown). This lack of an effect may have been the result of solarizing too late in the fall or the cold temperatures in February that killed flower buds and plants. Weed Control Weed control in response to soil treatments varied by species. There was no difference in the number of annual dicots per plot between fumigation and solarization plots in 1988, and both treatments had fewer annual weeds than the control plots did (Table 12-7 and Table 12-8). In 1989, fumigated soil had fewer annual weeds than did untreated soil, and plots treated by solarization had intermediate weed populations. Fumigation was the only treatment that controlled yellow nutsedge (Cyperus esculentus) in both years. No attempt was made to distinguish between C. esculentus seedlings and regrowth from tubers, but most plants resulted from established tubers, not seeds. In other research plots, purple nutsedge (Cyperus rotundus L.) germinated from seeds and was controlled by solarization (Table 12-8). Chicken manure also reduced the annual weed populations. The combination of solarization and chicken manure resulted in the lowest weed density. At Poplarville, weeds were not affected by solarization (data not shown).
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS Nematode Control Root-knot nematodes were not observed on plant roots in 1988. Highly variable nematode populations, with no significant differences across treatments, occurred in the spring of 1989. Fewer nematodes were observed in solarized soil than in the control plot in the fall of 1989 (Table 12-9). Compared with fumigated soil, solarized soil had similar levels of ring nematodes but more free-living nematodes. Soil incorporated with the sorghum cover crop had increased ring nematode levels compared with the untreated soil, while chicken manure reduced the levels of ring nematodes and increased the levels of free-living nematodes. Nematode populations (primarily Pratyulenchus spp.) at Lubbock in 1989 were reduced by 85 to 90 percent and 90 to 95 percent by solarization and chemical fumigation, respectively (data not shown). In general, solarization provided a level of temporary control over nematodes in the field that was less efficacious than that provided by fumigation. Soil Chemistry Solarization increased soil pH and ammonium (NH4) levels, while soil electrical conductivity and calcium, magnesium, and nitrate (NO3) levels were reduced on solarized soil compared with those in untreated soil (Table 12-10). Manure applied before solarization markedly increased soil pH, electrical conductivity, potassium, calcium, magnesium, phosphorus, ammonium, zinc, manganese, and copper. The electrical conductivity and soil solution P, K, and calcium concentrations were also higher in leachate collected under soil treated with manure (data not shown). TABLE 12-9 Solarization, Manure, and Cover Crop Effects on Ring and Free-Living Nematode Populations at Overton in 1989 Number of Nematodes/500 ml soil Treatment Ring Free-Living Solarization 38a* 569b* Fumigation 0a 331a Control 182b 790c Manure 9a 737c Manure + sorghum 174c 651b Control 40b 300a * Different letters indicate separation of the means within columns by Duncan's test at the 0.05 percent level.
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS TABLE 12-10 Effect of Solarization and Manure on Soil Fertility Parameters at Overton Concentration (mg/kg) Treatment pH EC (dS/m) P NO3 NH4 K Ca Mg Control 4.8b* 0.6a 61 56a 16b 231 745a 59a Solarization 5.3a 0.3b 49 42b 46a 182 559b 45b NPK† 4.8b 0.4b 35b 50ab 34b 153c 546b 34c Manure (0 kg/ha)‡ 4.0b 0.3c 28b 41b 14c 130c 533b 36c Manure (550 kg/ha) 5.2a 0.4b 68a 51ab 21c 237b 734ab 61b Manure (1,100 kg/ha) 5.4a 0.7a 87a 54a 53a 305a 794a 75a NOTE: EC, electrical conductivity; P, phosphorous; NO3, nitrate nitrogen; NH4, ammonium nitrogen; K, potassium: Ca, calcium; Mg, magnesium. * Different letters indicate separation of the means within columns by Duncan's test at the 0.05 percent level. † NPK, 250 lbs/acre of nitrogen, 40 lbs/acre phosphorus, and 75 lbs/acre potassium. ‡ Application rates were based on the total nitrogen content of the chicken manure. Discussion Solarization resulted in strawberry yields comparable to those obtained with typical production systems located in areas with a hot summer climate. Solarization was not as effective as fumigation in certain areas, for example, in eradicating difficult to control perennial weeds (yellow nutsedge). The failure of solarization to eliminate perennials with an established deep root system, rhizomes, or tubers confirms results of previous studies (Pullman et al., 1984; Rubin and Benjamin, 1984). Poor control of perennial weeds was likely the result of a failure to achieve lethal heating below soil depths of 4 to 8 inches. Cyperus spp. can survive temperatures of greater than 140°F (Rubin and Benjamin, 1984). For most situations, however, control of annual weeds with solarization is sufficient to allow for production without herbicides or fumigation. Obvious symptoms of plant diseases caused by soilborne pathogens were not indicated in these experiments. Pathogenic fungi or nematodes may not have limited yield. High populations of C. esculentus could account for the reduction in the yield with solarization compared with fumigation, but not for the increase in yield associated with solarization compared with the control. The reduction in annual weeds with solarization may explain some, but not all, of the increase in yield over that in untreated soil. In several other studies on solarization, increased plant growth response has also been reported in the absence of major soilborne pests (Katan, 1981; Stapleton and Devay, 1986). Modification of the soil pH or nutrient availability may also have been responsible for the increased plant growth re-
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS sponse. The effect of solarization on nutrient availability in these experiments likely would have been attenuated by the fertilization program. Much remains to be discovered about the complex biological interactions of the rhizosphere, as discussed by R. James Cook in Chapter 3. A concern that growers may have with the use of solarization is the selection of an appropriate type of plastic (ultraviolet stabilized). In the solarization system described here, the plastic should last for at least 1 year under field conditions. This allows for the plastic to be in the field for 2 months for the solarization period, sprayed white, planted with strawberries, and then replanted with melons the following summer. Several earlier attempts at solarization were not completely successful because the plastic's integrity did not last for longer than 4 to 5 weeks. In an initial evaluation of the effects of different types of polyethylene on soil heating, no major differences in film types were detected. One method that did enhance solar heating by several degrees was to decrease the soil albedo (darken) by spreading manure on the soil surface prior to solarization. Typically, soils in the South have insufficient soil N because organic matter is low and NO3 and NH4 are readily leached out of the topsoil. The goal has been to attempt to build a supply of slowly released N and other nutrients in the soil, under the plastic, that could supply several sequential crops with adequate fertilization. Direct manure applications have resulted in the most vigorous plants at the lowest cost in comparison with a combination of winter and summer legume cover crops and manuring followed by a nonlegume cover crop (data not shown). The application of 20 tons of chicken manure per acre increased the soil availability of P and K levels by 100 and 260 lbs/acre in eastern Texas. Based on fertilizer rate-soil analysis correlation data, the application of 1,000 and 900 lbs of P and K per acre, respectively, from commercial fertilizer sources produced an equivalent increase in the levels of P and K in soil. The application of 20 tons of poultry manure ($240 delivered cost within 50 miles of the source) per acre would provide the equivalent of approximately $300 of commercial fertilizer if only half of the N were available (500 lbs/acre). An economic evaluation of strawberry production with solarization compared favorably with fumigation and was advantageous over no treatment of the soil. Comparative enterprise budgets for conventional and solarization and manure systems are presented in Table 12-11. This analysis assumed very conservative production costs and fruit prices ($0.55/lb), and a 10 percent greater yield by fumigation over that by solarization. The solarization and manure system would cost $275 less per acre than fumigation and conventional fertilization, and $150 more than black plastic, conventional fertilization, and hand weeding. Assuming a 10 percent yield differential between the fumigation and solarization systems and assuming that the price received for fruit is of equal value, the conventional system
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS TABLE 12-11 Farm Enterprise Budget for Strawberry Production Using Different Cropping Systems System Analysis Cost ($)/Acre of Strawberries Nutrient inputs* Option 1: Chicken manure delivered and spread at 15 tons/acre† 240 Option 2: 600 pounds of 13-13-13 NPK fertilizer/year + 10 supplemental N applications at 20 lbs/acre through a drip line 165 Soilborne pest control‡ Option 1: Black plastic + hand weeding 375 Option 2: Solarization (cost of plastic laying, pigmenting, occasional hand weeding) 450 Option 3: Fumigation (custom application) 800 Yield comparison§ Average differential in total yield between conventional and low-input solarization systems (2 years of data) = 10 percent Average differential in total yield between solarization system and black plastic without fumigation (2 years of data) = 18 percent Cost ($) Sample Budget Analysis|| Conventional Solarization Black Plastic Nutrient inputs 165 240 165 Soilborne pest control 800 450 375 Other production costs 3,000 3,000 3,000 Total cost 3,965 3,690 3,540 Marketable yields (lbs/acre)# 12,000 10,800 8,856 Net returns at $0.55/lb 2,635 2,250 1,331 Net returns at $0.60/lb 3,235 2,790 1,774 * Costs are based on direct cost for supplies plus services cost as derived from the 1988 Texas Custom Rates Statistics Handbook. † Cost of manure is based on rates in eastern Texas, which depend on distance from source ($8/ton delivered within 20 miles, $12/ton for 20 to 50 miles). ‡ Assumes that cost for control of fruit decay is the same for all systems. § Differentials are based on 2 years of data. Data comparing yield as a function of nutrient input sources is not yet available. ||The estimates for these costs, yields, and returns are conservative. #Assumes a conservative total yield for conventionally grown fruit of 16,000 lbs/acre with 25 percent loss because of cullage. Yield differential between systems are estimates from 2 years of data.
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS is 15 percent more profitable than the low-input system. With only a $0.05/ lb price differential between low-input and conventional fruit, however, the solarization system has a 5 percent greater return. The solarization system was more profitable than the system in which just black plastic and hand weeding were used. Solarization would also enable the grower to capitalize on the organic market niche. Additional advantages of solarization would be the avoidance of restricted-use pesticides and elimination of specialized fumigation equipment. Alternatively, solarization in combination with fumigation may substantially decrease the level of fumigant used (Stapleton and Devay, 1986). CONCLUSION Results of this project have been presented at numerous growers meetings and field days. It is too early in the evaluation of these systems to estimate their potential significance and use by growers. Although these systems are effective replacements for conventional chemical input systems, the management intensity required for the successful use of the whole system may limit their use to only the most proficient growers. Individual components of these systems, however, could be adapted to other small fruit production and horticulture enterprises in the region or the nation. REFERENCES Hartz, T. K., C. R. Bogle, and B. Villalon. 1985. Response of pepper and muskmelon to row solarization. Horticultural Science 20:699–701. Katan, J. 1981. Solar heating of soil for control of soilborne pests. Annual Review of Phytopathology 19:211–236. Patten, K. D., E. W. Nuenedorff, G. Nimr, S. C. Peters, and D. C. Cawthon. 1989. Growth and yield of rabbiteye blueberry as affected by orchard floor management practices and irrigation geometry. Journal of the American Society for Horticultural Science 114:728–732. Pullman, G. S., J. E. De Vay, C. L. Elmore, and W. H Har. 1984. Soil Solarization—a Nonchemical Method for Controlling Disease and Pests. Leaflet 21377. Oakland: Cooperative Extension of the University of California. Putnam, A. R. 1988. Allelochemicals from plants as herbicides. Weed Technology 2:510–518. Rubin, B., and A. Benjamin. 1984. Solar heating of the soil: Involvement of environmental factors in the weed control process. Weed Science 32:138–142. Stapleton, J., and J. E. Devay. 1986. Soil solarization: A non-chemical approach for management of plant pathogens and pests. Crop Protection 5:190–198. Wagger, M. G. 1989. Time of desiccation effects on plant composition and subsequent nitrogen release from several winter annual cover crops. Agronomy Journal 81:236–241.
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS 13 Reactor's Comments Research and Education in the South Raymond E. Frisbie This reaction is to three sustainable agriculture projects in the southern region described in the following chapters: “Southeastern Apple Integrated Pest Management” by Dan L. Horton and colleagues, “Low-Input Crop and Livestock Systems in the Southeastern United States” by John M. Luna and colleagues, and “Solarization and Living Mulch to Optimize Low-Input Production System for Small Fruits” by Kim Patten and colleagues. In general, the three projects described in those chapters have made very good progress in organizing and beginning their respective research and education projects. The projects dealt at the whole-farm level and involved interactions with related cropping or habitat systems. There was a definite sense of a farming systems approach. Although limited success was reported or expected because of the newness of each project, it was clear that the funding period for these types of research and education projects is far too short. Whole or mixed farm systems that consider multiple variables require several years of study to achieve reliable results. In this reactor's opinion, 2 to 3 years of funding is not adequate. Funding for 4 to 6 years is more realistic. For example, the STEEP program in Washington and surrounding states has been ongoing for several years with a singular focus on erosion control. The benefits of this program are only now being fully realized. The Georgia low-input sustainable agriculture (LISA) apple production program described by Dan Horton and colleagues was well designed to
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SUSTAINABLE AGRICULTURE RESEARCH AND EDUCATION IN THE FIELD: A PROCEEDINGS consider horticultural, pest management, and erosion control factors. Market considerations regarding the timing of supplying fruit of high quality were evident in the program's design. The authors indicated they were accomplishing improved integrated pest management (IPM) of codling moth, red-banded leafroller, other insect pests, and plant pathogens through an integrated approach of pheromone trapping, phytosanitation, and habitat management. Intensive field sampling for insect pests and plant pathogens was used to time pesticide applications. Although a fairly comprehensive IPM system was discussed, the authors narrowly defined IPM as a “scout and spray program.” This observation was pointed out. The crop and livestock sustainable agriculture project at the Virginia Polytechnic Institute and State University described by John Luna and colleagues had, by far, the best system design in that it considered multiple production components and interactive linkages. It was clear that this interdisciplinary group had spent considerable time constructing a conceptual model on the operation of a fairly complex forage and livestock system. The group is to be complimented for using an innovative cover crop strategy that reduces erosion and provides supplemental nitrogen and for using a cultural management technique that controls armyworms and reduces insecticide use. Consideration of the impact of various forage production systems on calf weight gain and performance completes a very sophisticated system that should provide insight into the establishment of a sustainable system. The project at Texas A&M University described by Kim Patten and colleagues that deals with strawberries and blueberries in eastern Texas is a good example of how to design a sustainable agriculture system in soils with extremely low levels of organic matter and that receive low levels of rainfall in summer. Although this research program has been under way for only a short time, it has shown that ground cover and other management strategies that may work in some areas of the country are not suitable everywhere. The group at Texas A&M University is to be congratulated for examining a series of innovative approaches, such as soil solarization for plant pathogen and nematode control. The fact that some of these techniques did not give positive results was not discouraging. It is as important to know what will not work in a sustainable agriculture system as to know what will work. The research and extension faculty working on all three projects showed a very positive synergism in the development and conduct of their projects. They are to be congratulated.
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Representative terms from entire chapter: