Drift, droplets and ‘doughnuts’


News staff writer

February 28, 2007

A one-season trial on reducing spray drift of pesticides in orchards will continue this summer at the Mid-Columbia Agricultural Research & Extension Center.

Researcher Kelly Wallis said even with just last summer’s research, the OSU Extension Service center has some recommendations for growers that are effective and cheap.

“The questions we tried to address were how to affect the drift, how well did coverage work and what were the vegetative barrier types that worked,” she said.

She presented the findings of her and entomologist Helmut Riedl’s work at the Feb. 20 Winter Horticulture meeting. A separate study on the types of sprayers was presented by Paul Jepson, director of OSU’s Integrated Plant Protection Center.

Wallis’ team used sites near Mill Creek and Three Mile Creek in the vicinity of The Dalles. She said the intent was to keep the experiments simple and use what already existed. She said that the team wanted to look at what type of vegetative barriers would work best to keep spray out of salmon-bearing streams. They also wanted to see how using different types of sprayers could be more effective for growers.

Their study involved luminescent tracer dye that the team sprayed and 15-foot-tall poles erected to “catch” the spray. Wallis said because the dye faded quickly, the team had to spray and then run hard to collect the samples.

The team found that further study is needed to discover what types, how tall and what thickness of vegetative barriers work best to block spray drift. Jepson followed Wallis’ talk at the Pine Grove session and gave information on a summary of the different types of sprayers used in the research. Jepson and Nagajeran Ramalingam worked on the equipment portion of last summer’s trial.

“Drift happens,” Jepson said. “To help in avoiding drift, use weather forecasts to see when the best days are to spray.”

Jepson recommended growers use the Northwest Weather Service graphical forecasts. He advised that their maps of wind speed and direction were well-suited to the needs of Mid-Columbia farmers.

“The best conditions are a neutral, mild breeze to carry spray down into the foliage,” Jepson said. “This is a windy area; I sympathize with you.”

Conclusions for the different types of equipment showed that airblast sprayers had better coverage but higher drift. The team found that a plywood “doughnut” attached to an airblast sprayer was cheap and effective at reducing drift.

The team discovered that a plywood doughnut that covered half the area of air intake worked best for dormant season, while covering two-thirds of the air intake worked the best for the early to mid-season.

She also advised that when growers go to replace equipment that they consider tower sprayers and putting air induction nozzles on an airblast sprayer. Jepson said this change creates a bubblier droplet, which makes the spray drop sooner.

“There is a trade-off with the right-sized droplets at the right place at the right time,” he said.

The team also used Electrostatic, Hardi Tower, Proptec, Accutec, and Cropland sprayers in the studies.

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