tinue to determine the most efficacious way to reduce drift using physical barriers.

Researchers are examining other methods for selective application of a pesticide that targets the pest while minimizing application to nontarget organisms. Such methods should decrease the volume of pesticide spray while maintaining efficacy. Weed-sensing sprayers that use red and near-infrared sensors to detect the presence of green tissue have been successfully used in chemical fallow and hooded sprayers to reduce herbicide use by 14-90% (Ahrens1994, Hanks and Beck 1998, Blackshaw et al. 1998b.) However, these sensors and accompanying analytical equipment are relatively expensive, and the sensors are limited by the size of the weed that can be detected and are affected by environmental conditions, such as soil type, and wind speed (Blackshaw et al. 1998a).

The use of baits in combination with a pesticide has the potential of reducing the amount of a pesticide applied while maintaining efficacy. For example, the amount of malathion insecticide needed for control of Mediterranean fruit fly (Ceratitis capitata) in Israel was reduced from 1 kg/hectare to 150 g/hectare through the use of baits (Grinstein and Matthews 1997).

One of the biggest reasons for overapplication of pesticides is variation in the speed of the application equipment. New technology that constantly monitors ground speed and adjusts the application of the pesticide accordingly is being developed. The primary means of adjusting application rate is to alter the pressure of the spray. However, because the performance of many spray nozzles is pressure-dependent, applicators are limited in how much they can alter the pressure without affecting the distribution pattern of the spray (Paice et al. 1996). Other systems under development include use of a direct-injection system in which the spray volume is kept constant but the amount of active ingredient is varied (Ghate and Perry 1994).

Precision-agriculture techniques are new technologies under development that can vary the amount of herbicide application. In the future, users might map a field to identify locations of various weed populations and then select the amount and type of herbicide spray that match the weed density and population for that area of the field (Paice et al. 1996). One of the main limitations in adopting these mapping and sensor technologies is the need for sprayer technologies with rapid response and rate controllers that can automatically adjust the amount of active ingredient. Injection-metering devices, twin fluid nozzles, pulsed-nozzle systems, and rotary-spray generators with prediluted herbicides can decrease response time to less than 1 second.

Finally, one of the major risks in pesticide application is exposure of the applicator during the mixing procedures and disposal of used con-

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