Orchard research wants to conquer spray drift concerns


SALEM, Ohio – No doubt neighbors of many of Ohio’s orchards step across the property line and pluck a sweet apple or two from the crop.

Is that their compensation for putting up with spray drift, those uncontrollable droplets of everyday herbicides and pesticides used to protect the crop that inevitably visit their property, too?

Scientists are conducting research at the Ohio Agricultural Research and Development Center in Wooster and on Ohio State University’s main campus to determine the scope of spray drift: how far it goes and how it can be contained.

Those results will keep neighbors happy and help farmers use crop protection more efficiently.

Hot topic. Spray drift is a hot topic with the Environmental Protection Agency, according to Richard Derksen, a researcher in Wooster.

“We’ve got to minimize the intrusion [of drift] onto other people’s property,” Derksen said in a presentation during the Ohio Fruit Growers Society summer tour June 30.

The scientists’ findings will help the EPA come up with guidelines on how much drift is too much, and how to keep more of the spray inside the orchard, he said.

At Wooster farm. At the OARDC’s horticulture research farm near Guerne, scientists have erected test towers to measure concentrations on the ground and in the air.

They’re measuring droplets in the air from 3 to 33 feet above the ground, and 300 feet away from the apple trees sprayed.

“The experiments are the worst-case scenario because we’ve sprayed the outside rows,” Derksen said.

How far? In their tests, researchers are finding spray drift even at 33 feet above the ground.

“What does that tell us? It is probably going higher and we don’t know where the cutoff is,” he said.

“While we may not be able to see it, it’s a problem.”

In tests, less than 1 percent of the spray drift was detectable 100 feet from the trees 15 minutes after spraying. Less than 3 percent was detectable at ground levels.

“This is relatively small, but this is the stuff that will get you in trouble if the neighbors find it,” Derksen said.

Other options. Derksen and tour participants agreed the easiest way to reduce drift is to make bigger droplets through the use of low-drift spray nozzles.

Another option is drift retardant chemicals, though their effectiveness continues to be questioned.

An Ohio State University agricultural engineering study has shown that the products live up to their purpose.

The study examined the effects of drift retardant chemicals on spray pattern, droplet size and spray drift.

Sticking together. “Spray drift is a serious concern for all who apply pesticides. Yet many wonder if these products actually do what they advertised to do: reduce drift,” said Erdal Ozkan, an Ohio State agricultural engineer with the Department of Food, Agricultural and Biological Engineering.

Ozkan said if the chemicals are used at labeled rates, they do reduce spray drift. Gums added to raise the viscosity make bigger droplets that are less likely to drift.

Differences. In the Ohio State study, Ozkan and his colleagues tested five drift retardant chemicals and found that, in comparison to spraying only water, all the products reduced the percent of spray volume contained in small droplets, but at varying magnitudes.

“For example, the reduction of spray volume contained in droplets smaller than 100 microns ranged from 30 percent with the least effective product, to 68 percent with the most effective product,” said Ozkan.

“There is a direct correlation between the amount of active ingredients in the spray mixture and effectiveness of the spray mixture in drift control.

“The higher the active ingredient amount, the more effective the fight against drift is.”

Active ingredients. Which means, said Ozkan, that when buying drift retardant chemicals, growers should always read the label and compare products based on the active ingredient concentrations, and the total cost of making a mixture of a tank full of spray solution.

“Some products are expensive but require only a few ounces per 100 gallons of mixture, while others, containing the same active ingredients but at a much lower concentration, may be less expensive,” he said.

Efficacy. Ozkan also stated that some drift retardant products lose their effectiveness when passed through a typical sprayer pump.

“Some studies have found that some of these polymers tend to be sheared by passing through a sprayer pump, as would occur in a normal bypass, hydraulic mixing in common agricultural sprayers.

“This means that the drift retardant would lose its ability to increase droplet size – its ability to reduce drift – as the spray tank became empty,” said Ozkan.

Available. More than 30 drift retardant chemicals are commercially available to pesticide applicators, but Ozkan encourages growers to use the products as a last resort.

“In most cases, using low-drift nozzles and operating sprayers at lower pressures seems to be a better and more cost-effective approach to reducing spray drift,” said Ozkan.

“Drift retardant chemicals should be used as the last source of defense against drift, not the first.”


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