an increase in leaf coverage for the top leaves with increasing airspeed, and a better coverage in the middle Conventional over-the-row sprayers achieve very little deposit on of the canopy at full airspeed. At 94 L ha Ϫ1 , the top leaves near the ground and on the underside surfaces of leaves throughout the canopy. Air assistance has the potential to improve leaf coverage was not affected by increasing airspeed. deposition of droplets on these leaf surfaces. To gain some insight However, middle leaf coverage of the canopy was the on the effect of air assistance, the effects of airspeed, airflow rate, best at the highest airspeed. and air jet orientation were isolated. The study was carried out in On potatoe (Solanum tuberosum L.), Cooke et al. a spray chamber with a standard spray boom over micro-plots of (1990) obtained a better coverage for the middle and greenhouse grown broccoli (Brassica oleracea var. botrytis L.) plants.lower parts of the canopy with high airspeed (36 m s Ϫ1 ). Air was delivered slightly behind the nozzles from a variable widthThe coverage of the top leaves was the best at a medium slot producing a uniform two-dimensional air jet. The orientation of airspeed (25 m s Ϫ1 ). Jeffrey and Taylor (1991) used a the air jet with respect to the vertical could be adjusted from Ϫ10 to Hardi Twin air-assisted sprayer at three airspeeds (15, 40؇. The ranges of the independent variables were airspeed, 0 to 36 22, and 28 m s Ϫ1 ). On the upper side of leaves, they m s Ϫ1 ; airflow rate, 0 to 1.3 m 3 s Ϫ1 m Ϫ1 , and air jet angle, Ϫ10.2 to 40.2؇. Two sets of flat fan nozzles (Volume Median Diameter ϭ 230found that the coverage in the upper section of the and 400 m, both delivering 250 L ha Ϫ1 at 6 km h Ϫ1 ) were used to canopy was lower with increasing airspeed while at the carry out two full sets of experiments. Results showed that airspeed

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