Nature of exposure is a fundamental driver in nontarget terrestrial plant risk assessment for pesticides; consequently a novel study was designed to generate field-based drift exposure and evaluate corresponding biological effects of the herbicide mesotrione. The approach used a combination of US guideline drift reduction technology and vegetative vigor approaches. In each of 3 independent replicate spray application trials, 10 pots each of lettuce and tomato were placed at distances of 10, 20, 30, 40, and 50 ft (∼3, 6, 9, 12, and 15 m) from the downwind edge of the spray boom. Each application was conducted using a commercial 60-ft (18-m) boom sprayer fitted with TeeJet Technologies TTI110025 nozzles, with a nominal application rate of 0.2 lb a.i./A (224 g a.i./ha). The environmental conditions required by the protocol (air temperature 10-30 °C and wind perpendicular to the swath (±30°) blowing toward the plants at a mean wind speed of ≥10 mph [≥4.5 m/s] measured at 2.0 m above the ground) were met for each application. Following exposure, plants were transferred to a greenhouse for the 21-d vegetative vigor phase of the study. Symptoms of phytotoxicity and plant height were assessed at 7, 14, and 21 d after treatment. On completion of the 21-d after treatment assessment, all plants were harvested and dried in an oven to determine shoot dry weight. The biological data indicated that no statistically significant effects were observed at a distance of 30 ft (∼9 m) from mesotrione drift at wind speeds of ≥10 mph (10.9-12.4 mph); this endpoint (30 ft) is defined as the no observed effects distance (NOED). Environ Toxicol Chem 2017;36:2465-2475. © 2017 SETAC.

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SUMMARY Counts of Aphis fabae Scop, eggs in winter and of the active stages in May on the spindle bush, Euonymus europaeus L., are used to predict the need for chemical control of the black bean aphid on spring‐sown field beans, Vicia faba L. For the purposes of forecasting, most of England south of the Humber is divided into 18 areas for which separate forecasts are made. A level of 5 per cent of plants colonized on the SW. headlands of fields in early to mid‐June is used as an economic threshold above which control measures are justified. From 1970 to 1975, area forecasts of the probability of attack were successful. According to the sampled fields there was considerable annual variation in the size of infestations, ranging from widespread, potentially damaging populations in 1973 and 1974 to very small populations in 1975. There was also considerable variation between areas: for example, in East Anglia and the East Midlands treatment was justified only in 1973 and 1974, whereas in Hampshire and Worcestershire/Herefordshire treatment was justified in all years except 1975. It was estimated that, from 1970 to 1975, control based on forecasting would have led to a gain of £11·4/ha over no treatment, and £3·8/ha over correctly timed routine preventive treatment applied annually irrespective of the aphid situation.

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