Strategies to Minimize Spray Drift
By: Erdal Ozkan, Professor, Extension Pesticide Application Technology Specialist, FABE-OSU
For many reasons, including production costs, safety, and the environment, it is important to maximize pesticide deposits on the target when spraying. Spray drift is a major challenge to pesticide applicators trying to achieve this goal. Although complete elimination of spray drift is impossible, it can be significantly reduced by awareness of its major causative factors, and by taking precautions to minimize their influence on the off-target movement of droplets. Extensive information related to factors influencing spray drift is in the Ohio State University Extension publication (FABE-525) “Effect of Major Variables on Drift Distances of Spray Droplets”.
The risk of drift is considerably higher when spraying in orchards and vineyards compared to spraying in field crops for three main reasons:
- The target being sprayed in field crops is relatively uniform, it’s a short distance from the nozzles, and the droplets are directed downward. The target in orchards and vineyards is not uniform in size and shape (there may be gaps in canopy), there is a much longer distance from the nozzles, and the droplets are directed in an upward trajectory.
- The type of sprayer used in field crops releases the droplets downward just over the target. The sprayer used in orchards and vineyards uses a powerful fan that blows droplets in a horizontal and upward trajectory, making the droplets much more susceptible to drift.
- The type of nozzle and droplet size used in field crop spraying is most often a flat-fan nozzle that discharges relatively large droplets. Orchard and vineyard sprayers are generally equipped with hollow-cone nozzles that produce very fine to fine category droplets.
Therefore, more precautions should be taken to reduce the drift risk when spraying in orchards and vineyards.
Strategies to Reduce Spray drift
Some factors that affect drift, such as weather conditions, are out of the control of the pesticide applicators spraying in orchards and vineyards. However, many of the factors affecting drift are under the control of the applicators. Here are some of the key cost-effective and practical strategies to reduce spray drift:
- Keep drift in mind when selecting your sprayer. Although the air-assisted (airblast) sprayer type shown in Figure 1 (with radial spray discharge) is used by most fruit growers in the U.S., many other less drift-producing types of air-assisted sprayers, such as the one shown in Figure 2 (with horizontal spray discharge) are used in other parts of the world. Sprayers producing horizontal air and spray flow generally produce less spray drift. Take a look OSU Extension publication (FABE-533) “Sprayers for Effective Pesticide Application in Orchards and Vineyards”, which provides a discussion of all major types of sprayers used in orchards and vineyards.
- Consider switching to low-drift nozzles. In the U.S., the typical sprayer used in orchards and vineyards is an airblast sprayer equipped with hollow-cone (most often) or conventional flat- fan nozzles (less common). Both nozzle types produce extremely fine, very fine, and fine droplets, which are highly susceptible to drift. Hollow-cone nozzles operated at high pressure are especially susceptible. In recent years, nozzle manufacturers have introduced new nozzles that significantly reduce the number of extremely small, drift-prone droplets. In other parts of the world— especially Europe— most growers are gradually switching to these low-drift air-induction nozzles to spray fruit trees.
- Spray pressure affects the size of droplets released from a nozzle. Higher pressure produces smaller droplets. Therefore, avoid operating the sprayer at high pressures. Although 200 to 300 psi is the norm for manU.S. growers when operating airblast sprayers, a pressure of 100 to 150 psi is more than adequate to generate the fine to medium size droplets that improve penetration and coverage on the target.
- Spraying in high winds, high temperatures, and low relative humidity increases the risk of spray drift. If weather conditions are not favorable, and there is a concern about spraying that might result in drift, wait for more favorable conditions. Review the forecast and schedule spraying accordingly. Use apps that provide current, local weather conditions and use that information to make sound decisions on when to spray. Be aware that wind speeds shown in apps display data taken from nearby weather stations that may not reflect the wind speeds in your specific spraying location. Therefore, it is best to carry a small hand-held, battery-powered wind meter (anemometer) to check the wind speed several times before and during spraying. The price of a wind meter is usually less than one-third the hourly fee a lawyer can charge a client sued for drift-related damages.
- Adjust the sprayer fan air-flow rate and volume so that the air being directed into the canopy replaces the air already in the canopy but dies down significantly as it reaches the other side of the canopy. A proper air adjustment results in very little spray droplets escaping the canopy. As a side benefit, reduced air assistance results in lower fuel consumption.
- The travel speed of the sprayer also influences spray drift. Even when adjustments are made to restrict air intake into the fan, too much air may reach the canopy if the travel speed is extremely low. Slow travel speeds allow the canopy to be exposed to the air flow for a much longer time, thus contributing to drift.
- When spraying the outer side of the last row, turn off the nozzles on the side of the sprayer that are pointed away from the canopy. In addition, if you are using a conventional airblast sprayer with radial air discharge, cover the air exit port on the side of the sprayer facing away from the canopy. Both actions further reduce the risk of spray drift.
- Carefully direct the air from the fan towards the canopy to ensure that the sprayed droplets are intercepted by the canopy. With conventional, radial discharge airblast sprayers, deflector plates must be installed on both the top and the bottom of the fan, and on both side of the sprayer, to guide the spray plume toward the canopy and at a level equal to the canopy's height. The size of the deflectors should be big enough to effectively direct the air at the canopy.
A successful spray operation in orchards and vineyards achieves maximum efficacy from the pesticide applied while minimizing the off-target (drift) movement of pesticides. Spray drift poses health risk to nearby people and animals, increases the risk of polluting natural resources like air and water, and wastes pesticides that could have been used to treat pests in orchards and vineyards. A brief discussion on practical ways to reduce spray drift is discussed in this article. More comprehensive information on this topic is given in the Ohio State University Extension publication (FABE-535) “Strategies to Minimize Spray Drift for Effective Spraying in Orchards and Vineyards”.
Tags: Effective Spraying, Pest Management, Viticulture