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When grass is green, white mould is keen

When grass is green, white mould is keen

Tips for effective soybean fungicide application and resistance management

By Jonathan Martin
Staff Writer

As a mid-July heat dome releases eastern Canadian producers from its swelter, another challenge is raising its pale head.

White mould, a soybean-loving fungus, likes moderate temperatures and wet weather. Ontario has plenty of each now, so Rob Miller, a technical development manager for BASF, told the best ways producers can prepare to meet the problem of this mould head-on.

“We like to say, ‘when the grass is green, white mould’s keen,’” Miller said. “In July, if your grass is doing really well and you’re seeing a few mushrooms pop up here and there, you’ll probably see some fungus in your soybeans as well.”

White mould needs the same conditions as lawn mushrooms to grow apothecia, its spore delivery-system. The spores fly off the apothecia, land on the soybean plants and infect the crops.

White mould feeds on the oilseed’s flowers, so the crop is at its highest risk during the R2 growth stage.

Farmers should keep their eyes on their fields with high plant populations, narrow row spacing, shorter crop rotations or a history of manure use, Miller said. White mould likes those fields best.

“As far as fungicide goes, you’ll want to apply it to the fields with the most yield potential,” Miller said. “Apply (fungicide) using a nozzle that provides medium-to-coarse droplet sizes that can get down into the plant. Cover the top of the leaf, under the leaf and the flower.”

Misusing fungicides can lead to other problems, though, Miller said. As conversations around weed resistance heat up, some agronomists are turning their attentions to the possibility of developing a similar problem with fungicides.

So far, Canadian producers have managed to stave off fungicide resistance in soybeans but American farmers are having issues with frogeye leaf spot fighting off their treatments.

“In the U.S., (farmers) do a lot of soybean-on-soybean rotations,” Miller said. Producers “also use fungicides with the same active ingredient year after year. In Ontario, we tend to do a better job with our rotations.”

Switching between soybeans, wheat and corn helps prevent fungi from developing resistance. Using multiple effective modes of action helps, too. Farmers are no stranger to checking their herbicide labels to make sure they have different active ingredients. They should following the same strategy when attacking fungi, Miller said.

“Getting the application timing right is important to reducing resistance as well,” he added. “Don’t be reactive. Follow the label and use full label rates. Don’t use cut-rates.”

If a producer is on-the-ball over the next couple weeks, his or her crop will probably do well, as far as white mould is concerned, Miller said.

It’s been a tough year but this fight is one that it’s not too late to win.

Joao Bento da Silva/iStock/Getty Images Plus photo

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