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May 1, 2003

Purdue experts want farmers to 'catch the drift'

WEST LAFAYETTE, Ind. - A pair of Purdue University specialists hope farmers "catch the drift" from their herbicides and other farm chemicals before their neighbors do.

"Most producers are aware of spray drift and try to combat it," said Glenn Nice, a Purdue Cooperative Extension Service weed scientist. "But it's important to review application practices because more and more people are moving from cities to rural areas, and a farmer's new neighbors might not appreciate spray drifting to their yards and gardens.

"I had one complaint not too long ago, where a family had moved out from the city and was living near a field. One day the farmer sprayed. The homeowners were unaware this was going to happen and left all the windows open. When they came home, they found the house smelled like whatever was sprayed.

"What could have solved that problem right off the bat was to notify the family about the spraying that day. That's all they really wanted. Communication is a wonderful thing and can solve a lot of problems before they occur."

Most importantly, Nice said, "Try not to fall into the trap of declaring, 'I need to spray right now.' It's always a good idea to try to schedule yourself so you have more options than just one day to spray."

When it is time to spray, there are two issues a farmer must address to avoid drift, Nice said. Those are: decreasing the amount of time it takes for the chemical to travel from the boom to the plant; and avoiding factors that could make the chemical travel where it shouldn't.

The most obvious way to combat spray drift is to avoid spraying when it's windy. "It's a good idea to know wind speeds," Nice said. "In fact, most herbicides now have a maximum wind speed on the label, which makes wind speed more of a legal matter than it was before."

Mornings and evenings are the best time to spray, Nice said. However, during those times it's important to watch for inversion layers, which occur when a layer of warm air traps a layer of cold air beneath it. The warm air acts as a lid, and any particles in the air are forced to move laterally instead of up into the atmosphere. That means spray can drift horizontally for miles as a result of inversion layers, Nice said.

He suggested using smoke bombs or watching nearby smokestacks to determine whether inversion layers are in place. If they are, the smoke will travel upward to a point and then suddenly begin moving to the side.

Bill Johnson, an Extension weed scientist, said farmers also should keep track of humidity and temperature. Some chemicals are volatile and can evaporate into the air when temperatures are high. In addition, high temperatures and low humidity will result in water evaporation, which decreases droplet size.

Unlike wind and temperature, there are some aspects of spraying that farmers can control all the time. One is lowering boom height. If the boom is closer to the plants, the droplets reach the plants more quickly, and the chemical doesn't float away, Johnson said.

In addition to lowering boom height, increasing droplet size can decrease the amount of time it takes the chemical to travel to the plant, Johnson said. "The larger the droplet, the faster it falls, decreasing the likelihood of spray drift," he said. Nozzle selection and pressure adjustments can increase droplet size.

"It's always a good idea to change the nozzle out to get the volume of chemical you want, rather than just cranking the pressure up," Nice said. "Any time you push a fluid through a small opening you get what's called shear effect that causes small droplets, which drift more easily than large droplets."

Finally, it's a good idea to calibrate sprayers. Nice said proper calibration can mean saving money on chemicals and preventing spray drift. He recommends farmers calibrate their sprayers at least once a year.

"For research purposes we calibrate the sprayers every time we spray," Nice said. "You'd be surprised how much the calibration can change."

Johnson said, "The public is more aware of pesticide concerns. That means that farmers need to be conscientious about spraying and keeping records to protect themselves."

Writer: Kay Hostetler, (765) 494-6682, kjh@purdue.edu

Sources: Glenn Nice, (765) 496-2121, nice@btny.purdue.edu

Bill Johnson, (765) 494-4656, wgjohnso@purdue.edu

Related Web sites:

Purdue Weed Science Web site: http://www.btny.purdue.edu/weedscience/

Purdue Pesticide Programs: http://www.btny.purdue.edu/PPP/

Purdue News Service: (765) 494-2096; purduenews@purdue.edu


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