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April 30, 2007

It's OK to apply fungicides to row crops, but don't go hog wild

WEST LAFAYETTE, Ind. - Growers thinking of applying fungicides to row crops can do so, as long as it's done cautiously and sparingly, said a Purdue University expert.

Fungicides have been used for years by fruit and vegetable growers, but not much is known about the payoffs of fungicide application for corn and soybeans, said Greg Shaner, Purdue Extension crop specialist.

Growers that decide to apply a fungicide and want to test it out for themselves should choose portions of fields to spray at random, Shaner said. This will provide a better indication of yield results over choosing specific spots to treat because there may be a tendency to treat areas that historically have better yields, he said.

When analyzing yield results, remember other factors should be considered, such as soil type and moisture level, in addition to the fungicide treatment, Shaner said.

Because fungicides work better as preventatives rather than as curatives, application timing is critical, Shaner said. It is important to spray a crop just at the onset of disease, as most fungicides only remain effective for three weeks. Fungicides applied too early won't be effective when needed, while those applied too late won't stop the disease.

"A general guideline for corn is to make the first application when there are no more than a couple lesions on lower leafs of about half the plants in a corn field," Shaner said.

"We have the threat of soybean rust, but it hasn't yet been a problem in the Midwest. If it does appear during the summer, then we have got a definite problem, and we will need to use fungicides."

For ground application of fungicides, use 10 gallons per acre. Research at Purdue suggests 15 gallons per acre gives better coverage and canopy penetration than 10 gallons per acre. Five gallons per acre is the standard for aerial application, but a couple of fungicides can be applied at two gallons per acre.

Research is being conducted with electrostatic technology that requires only 1 gallon per acre, but it is not yet commercially available. As the fungicide droplets emerge from the spray nozzles, they are given an electrical charge that causes them to be attracted to the foliage. But because the droplets have the same charge, they repel each other and disperse in a more uniform pattern.

"This summer we are working with an aerial applicator to apply fungicides on corn and soybean fields at three different increments - five, two and one gallon per acre," Shaner said. "Our goal is to collect data on the amount of disease control, yield difference and bottom line resulting from applying a fungicide to both corn and soybeans."

In the weeks following the fungicide application, sprayed fields and unsprayed fields will be compared for disease control. Yield also will be compared after harvest.

Shaner said the aerial application trials will show if the decreased volume and smaller droplets provide the same disease control and yield benefit as conventional aerial application.

He said that some manufacturers believe fungicides have general plant health benefits, meaning that even though there may be no real foliar disease problem to control there are yield responses. While the fungicides are not actually controlling a disease, they may provide a boost to the soybean plant, Shaner said.

"It's possible that some of the late-season soybean diseases - such as pod and stem blight and anthracnose, which are not evident until the beans are maturing and starting to drop their leaves - may be doing more damage than we realized, and fungicides are controlling them," he said.

Unlike soybeans, spraying corn with a fungicide is more for disease control, Shaner said. But that is an area that still needs more research.

When determining whether to apply a fungicide, plant susceptibility also must be considered. 

"Among all the corn hybrids that are available, there is quite a range in resistance to leaf diseases," Shaner said. "Some have pretty good resistance, some not so good resistance and some are pretty susceptible. We anticipate that you would see a response and an economic return if you spray a hybrid that is fairly susceptible."

In spraying more susceptible hybrids, the leaf tissue is protected, and so is the yield, he said.

Writer: Julie Douglas, (765) 496-1050, douglajk@purdue.edu

Source: Greg Shaner, (765) 494-4651, shanerg@purdue.edu

Ag Communications: (765) 494-2722;
Beth Forbes, forbes@purdue.edu
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