Spray drift mitigation using opposing synchronized air-blast sprayers

Authors: VAN STEENWYK, ROBERT - University Of California; Siegel, Joel; BISABRI, BARAT - Shiraz Ranch Llc; CABUSALY, CHRISTIAN - University Of California; CHOI, JAMIE - University Of California; STEGGALL, JOHN - Dfa Of California; MACE, KEVI - Dfa Of California; BLECKER, STEVE - Dfa Of California; POE, PERRY - Dfa Of California; PETERS-COLLAER, STEPHEN - University Of California; KLASSEN, PERRY - Coalition For Urban Rural Stewardship

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2020
Publication Date: 10/21/2020
Citation: Van Steenwyk, R.A., Siegel, J.P., Bisabri, B., Cabusaly, C.S., Choi, J.M., Steggall, J.W., Mace, K.C., Blecker, S.W., Poe, P.A., Peters-Collaer, S.R., Klassen, P. 2020. Spray drift mitigation using opposing synchronized air-blast sprayers. Pest Management Science. 77(2):895-905. https://doi.org/10.1002/ps.6094.
DOI: https://doi.org/10.1002/ps.6094

Interpretive Summary: Pesticide drift is the airborne movement of pesticides away from the intended target, in this case tree nut orchards. Off-site movement of pesticides from air-blast speed sprayers is of particular concern when an orchard is adjacent to buildings, sensitive sites such as waterways, or to crops where the pesticide is unregistered. Previous recommendations suggested mitigating this problem by directing the spray inward for the outer rows of the orchard or by slowing the spray velocity, so that more pesticide remained in the tree. Unfortunately, coverage in the outer rows was sacrificed by these methods. In order for changes to be accepted they must provide excellent pesticide coverage with minimal cost. In this study for the control of navel orangeworm (NOW), the principal lepidopteran pest of tree nuts in California, we investigated two treatments employing two synchronized air-blast speed sprayers (both engine driven and power take off) driving and spraying parallel to each other, with the outside sprayer either spraying only air into the orchard (Air-In) and then one sprayer coming round and spraying insecticide into the orchard, or instead the outside sprayer applies insecticide into the orchard (Double Spray) while it is parallel to the inner sprayer. Our goal was to essentially create a wall of air to reduce drift. This technique was evaluated in almond, pistachio and walnut orchards and compared to the standard grower practice of spraying out of both sides of the spray rig between the first two rows, with pesticide directed outside the orchard. Treatment efficacy was assessed by several measures, including measurement of insecticide deposition at two sites within the canopy and by bioassay to confirm insecticide efficacy. Wind speed and wind direction were measured and used in the analysis. Off-site spray movement was measured by quantifying deposition of spray material at intervals from the orchard margin out to 150 feet in almonds and as far away as 400 feet in pistachios and walnut. The Air-In treatment consistently reduced drift for all tree nut orchards assessed and insecticide coverage was equal to the grower standard, while the Double Spray technique did not reduce drift but significantly improved coverage; it could be useful in almonds. We conclude that the Air-In technique shows great promise in reducing pesticide drift while maintaining or improving pesticide coverage with minimal cost to the grower.

Technical Abstract: Pesticide drift is the airborne movement of pesticides away from the intended target, in this case tree nut orchards. Off-site movement of pesticides from air-blast speed sprayers is of particular concern when an orchard is adjacent to buildings, sensitive sites such as waterways, or to crops where the pesticide is unregistered. Previous recommendations suggested mitigating this problem by directing the spray inward for the outer rows of the orchard or by slowing the spray velocity, so that more pesticide remained in the tree. Unfortunately, coverage in the outer rows was sacrificed by these methods. In order for changes to be accepted they must provide excellent pesticide coverage with minimal cost. In this study for the control of navel orangeworm (NOW), the principal lepidopteran pest of tree nuts in California, we investigated two treatments employing two synchronized air-blast speed sprayers (both engine driven and power take off) driving and spraying parallel to each other, with the outside sprayer either spraying only air into the orchard (Air-In). The air-blast speed sprayers used in our study were Air-O-Fan and Durand-Wayland. The Air-O-Fan speed sprayers have adjustable baffles and a diverter plate that could be closed, which would restrict most of the air flow. In all studies that used Air-O-Fan speed sprayers, the baffles and diverter plate were closed on the outer manifold. Durand-Wayland did not have adjustable baffles or diverter plate. An air collar was constructed with a 1.3 foot by 4.1 foot piece of diamond plate and bent to the shape of the Durand-Wayland manifold. The collar was bolted to the outer manifold and prevented the delivery of any air. After the tandem spraying a single sprayer was used to treat the outer rows spraying inwards. The second treatment (Double Spray) had the outside sprayer apply insecticide into the orchard while it was parallel to the inner sprayer. Our goal was to essentially create a wall of air to reduce drift. This technique was evaluated in almond, pistachio and walnut orchards and compared to the standard grower practice of spraying out of both sides of the spray rig between the first two rows, with pesticide directed outside the orchard. Treatment efficacy was assessed by several measures, including measurement of insecticide deposition at two sites within the canopy and by bioassay to confirm insecticide efficacy. Wind speed and wind direction were measured and used in the analysis. Off-site spray movement was measured by quantifying deposition of spray material at intervals from the orchard margin out to 150 feet in almonds and as far away as 400 feet in pistachios and walnut. The Air-in treatment significantly reduced insecticide drift between 53% to 99% at 25 feet from the orchard drip line when compared to the grower standard because this technique reduced or eliminated the air-output from the outside manifold and prevented the spray movement of pesticides that were sucked into the air intake. The Air-in treatment maintained or improved the amount of pesticide residue deposited (0.7 to 2.6 times) and the percent insecticde coverage up to 1.4 times with different air-blast speed sprayers .The Double Spray technique did not reduce drift but significantly improved coverage; it could be useful in almonds. We conclude that the Air-In technique shows great promise in reducing pesticide drift while maintaining or improving pesticide coverage with minimal cost to the grower.