Off-target loss in ornamental nurseries with different spray techniques

Information is lacking on spray techniques to reduce off-target loss on the ground and via spray drift from the treated area in nursery applications. Airborne deposits at three elevations on sampling towers and on the ground at several distances from the sprayer were investigated with the three spray treatments in an open field without crops. Tests were conducted with an air blast sprayer equipped with conventional hollow cone nozzles (HC), low drift nozzles (AI), and conventional hollow cone nozzles with a drift retardant (HCDR) in an open field without crops. To compare field test results, wind tunnel experiments were conducted to assess spray deposits on the floor beyond 0.4 m downwind distance from the nozzles and airborne deposits at 2.1 m downwind from the spray discharge point with the three spray techniques. Droplet size distributions across spray patterns were measured with a laser particle/droplet image analysis system. There was no significant difference in airborne deposits for the three elevations at both 15 and 30 m downwind from the sprayer between AI and HC methods except for 3.05 m elevation at the 15 m distance although the average airborne deposits with AI were lower than that with HC. The downwind spray deposits on the ground at 15 and 30 m from the sprayer with AI were higher than that with HC and HCDR. Compared with conventional hollow cone nozzles, drift reduction from air induction nozzles or the spray mixture with drift retardant was significant in wind tunnel tests but was not significant in field tests.