Spraying capacity critical for soybean rust control

U.S. farmers will have to beef up their capacity to spray soybeans with soybean rust fungicides if they hope to minimize crop losses from the devastating disease, which they are facing for the first time in 2005.

That's the conclusion of David Wright, one of the leading U.S. experts on soybean rust.

“I question whether we have enough capacity to treat soybean acres in the time necessary to protect yield,” says Wright, director of production technologies for the Iowa Soybean Promotion Board. “With soybean rust, you have a very narrow window of opportunity to treat after the infestation has occurred.”

Typically, fungicides designed to stop soybean rust after it has infected a field must be applied within two to three days to protect yield. “In four to five days, it probably is too late,” he says.

Currently, farmers and custom applicators don't own enough sprayers to treat the large number of acres that could need to be treated at the same time. “Unlike aphids, soybean rust will not be isolated,” he says. “It will show up in many areas all at one time.”

Wright notes that it is unclear how widespread soybean rust will be this year. Since rust can't over-winter at freezing temperatures, it must travel with the wind from southern states, where it was found in early November. However, he believes the disease is likely to infest Iowa and other Soybean Belt states in 2005.

Wright encourages farmers to develop a plan for treating rust after learning as much as they can about the disease. “There really isn't much else you can do but be prepared with a management strategy that might include deciding to make your own fungicide applications,” he says.

High-clearance trailer and mounted sprayers with the capacity to treat several hundred acres per day typically cost $30,000 to $50,000, notes Steve Claussen, president of Redball, LLC, Benson, Minn., a large sprayer manufacturer. “We expect more farmers to buy their own sprayers to prepare for soybean rust. They will use them to apply herbicides, too. Other farmers will be upgrading to larger sprayers to handle the job as quickly as possible.”

Wright notes that rust fungicides typically must be applied with 10 to 20 gallons of water to assure good coverage. The high carrier volume will put extra pressure on spraying capacity, since sprayers will be able to cover only half as many acres per fill than with typical herbicide carrier volumes.

Farmers wishing to reduce last-minute treatment hassles will have the option of applying a preventive treatment before rust strikes. These fungicides must be applied before first flower and prior to rust infestation. However, this approach forces growers to spend money for a treatment before they know it is needed, Wright says.

State officials from key soybean-producing states have approved several fungicides to treat soybean rust, which can cause total yield loss if left untreated. The cost of these fungicides has not been announced, but some fungicides are expected to cost $20 to $25 per acre.

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