long soil persistence are eliminated early in the discovery process unless there are other applications for which the compounds can be useful (for example, household pests).
Once a compound with the efficacy needed to control the pest with minimal impact on the environment and nontarget organisms is found, the development phase can begin. This is the most expensive part of bringing a new product to market. Development, testing, and registration can typically take 8-12 years and cost over $50 million for each pesticide (IANR 1994). Registration involves at least 142 tests, most of which are aimed at determining the environmental and toxicological characteristics of new compounds. EPA will register only those compounds that meet strict criteria for human and environmental safety. Industrial scientists must use this same battery of tests to maintain the registration of existing compounds.
Pesticide research and development have come a long way from the procedures used to find earlier compounds, such as DDT and related compounds. There is now a much better understanding of the desirable and undesirable characteristics of pesticides. Companies have set up systems to eliminate, early in the discovery phase, compounds that do not meet the new standards, to ensure that time and resources are not wasted on compounds that will not be acceptable as pest-control agents.
Pesticides effectively control many insects, diseases, and weeds. However, to be effective, pesticides have to target the crop or animal of interest. Pimentel (1995) estimated that only 0.00001-1% of the pesticides sprayed actually reach the target pests. The reasons for the low rate of interception are many, including the distribution of the pest, the size of the pest population at the time of application, uncertainty as to how and when the pest will encounter the pesticide, the use of broadcast sprays, and drift. One way to reduce the risk posed by pesticides is to increase the amount of pesticide that reaches the target pest while decreasing the total amount of pesticide applied to the field. That can be accomplished only through improvements in application technology (see table 3-1).
Spray drift is one of the biggest concerns regarding the movement of pesticides to nontarget organisms. Off-target losses can range from 50 to 70% of the applied pesticide because of evaporation and drift (Hall and Fox 1997). Drift from aerial applications is greatest and that from ground applications is least (Hall and Fox 1997).
There are several ways to reduce drift. One way is to use spray additives that affect the drop size of sprays by increasing the number of large droplets and decreasing the number of small droplets (Hall et al. 1993).