COLUMBUS, Ohio — Drift retardant chemicals may be an option to help reduce spray drift on field crops, but 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, conducted by Ohio State agricultural engineers, examined the effects of drift retardant chemicals on spray pattern, droplet size and spray drift.
"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. "Results of these tests indicate that if used properly at appropriate rates, these products indeed reduce spray drift by hindering formation of small, drift-prone droplets."
Drift retardant chemicals are normally made up of types of long-chain polymers or gums that increases the viscosity of the spray mixture, ultimately impacting the size of the droplets and the amount of spray concentrated in each droplet.
Yet, little research on the performance of the products has been documented. Results of one study conducted by USDA-ARS engineers in Texas, for example, indicated that the effect of polymer concentration on droplet size is dependent on polymer type, and that certain types of polymers increase droplet size, thereby reducing the percentage of spray volume composed of small droplets subject to spray drift.
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."
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. But they may require several quarts of product to achieve the same level of protection against drift," he said.
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. "Gums are not sheared as easily as the long chain polymers, and some types of polymers (poly-ethylene oxide) are sheared in fewer passes through a pump than other types of polymers (polyacrylamides)."
Over 30 drift retardant chemicals are commercially available to pesticide applicators, but Ozkan encourages growers to use the products as a last resort. "Although drift retardant chemicals are effective in reducing the number of drift-prone droplets, 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."