Disease triangle means more fungicide on corn

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More and more corn growers around Pratt, Kan., are making a fungicide application to their corn, said Vernon Flowers, an agronomist with Crop Quest.

Flowers contends that it is a field-by-field determination if a fungicide application would likely increase yield for a corn grower. He appreciates being able to hold off until the last minute to make a recommendation because he normally recommends a fungicide with curative and protective action. He also considers the disease resistance of the hybrid planted. He evaluates how heat and humidity are encouraging disease development, and he tracks the potential that disease spores have overwintered in fields or if spores are being blown in from the south.

Gray leaf spot is a major problem in southwest Kansas where growing corn on corn is common, and gray leaf spot has increased with farmers using less tillage to bury previous year's stalk residue. Crop residue is a breeding ground for various disease spores.

Flowers' growers use pivot irrigation to grow their corn.

"As the corn gets a little size to it, we make our own little environment inside that irrigation circle for fungus. We are always putting water to the corn through the center pivot, and it is hot and humid. That is what the spores like in order to multiply," he said.

In northern Iowa, fungicide treatment of corn-on-corn acres are almost an automatic treatment and many other growers rotating corn and soybeans believe in applying a fungicide from the VT to R2 stage of corn growth. Many growers have begun prepaying for their fungicide when they buy their other crop protection products prior to planting the corn, said Larry Cink, Bayer CropScience technical sales consultant for northwest Iowa.

Similar to what Flowers noted, Cink explained that the yield return from making an application of Stratego fungicide at the VT to R2 growth stage depends on the "disease triangle." He said, "You've got to have a host (corn), you've got to have the disease (pathogen) present and you have to have the appropriate environment for the disease (fungus) to multiply."

Also similar to Flowers, Cink noted that every corn grower has heard about the practice of late-season fungicide application and more of them are willing to pay for an application — usually by airplane — but a few are having the fungicide custom applied with the tallest of high-clearance sprayers. Most pivot irrigation growers are using chemigation.

There is a little more flexibility in timing of Stratego because it has a fungicide component with curative action (propiconazole) and one with preventive action (trifloxystrobin), Cink said. The use of a fungicide with two modes of action has appeal to growers, he said.

"A lot of farmers compare products and notice they could pay x-amount for a product that has only one mode of action or buy Stratego that has two modes of action for about the same price or even less," Flowers said. A 2010 price reduction for Stratego provided that competitive advantage, he explained.

Because a late-season application of Stratego has proven itself with a large share of growers, not just continuous corn growers, several early-adopter growers moved onto another fungicide agronomic practice this year — applying Stratego mixed with a post-emergence herbicide at the corn's V5 stage of growth to control early anthracnose leaf blight and eyespot that was a concern, Cink explained. Several fields were treated in his area.

Technical Sales Consultant Larry Cink can be reached for more information by e-mail at larry.cink@bayercropscience. com.

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