Soybean School: No payback for white mould revenge spraying

Photo: Daren Mueller

White mould is showing up in soybean fields across Ontario, especially in areas that have consistently seen wet weather and moderate temperatures throughout the summer.

In this episode of RealAgriculture Soybean School, OMAFRA plant pathologist Albert Tenuta explains that the fungicide timing for optimal control of white mould is as flowers emerge at the R1 and R1.5 stage. “That’s where the first application has been most beneficial because you are slowing down the initial infection,” explains Tenuta.

When growers experience challenging environmental conditions like we’ve seen in 2017, Tenuta says a second application at the R3 stage or a little later would be helpful. This is certainly the case when other risk factors – high populations, narrow rows, field history of the disease – are present.

Many growers, who are now seeing disease symptoms in their crop have asked whether there is value in spraying fungicides at the R4 or R5 stage. Tenuta says late application is more a case of revenge spraying than effective management. “Coming with a fungicide application at that stage may make you feel good and sleep better, but in most cases, you’ve wasted your money.”

At that stage, the fungicide is simply not going to be able to penetrate the canopy and get to the infection. “The disease still develops down there and, in many cases, pinches off and kills the stem,” Tenuta notes. “It’s not going to increase yield. It might green up the top part of the canopy, but overall the return on investment is just not there.”

Click here for more Soybean School episodes.

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Bernard Tobin

Bernard Tobin is Real Agriculture's Ontario Field Editor. AgBern was raised on a dairy farm near St. John's, Newfoundland. For the past two decades, he has specialized in agricultural communications. A Ryerson University journalism grad, he kicked off his career with a seven-year stint as Managing Editor and Field Editor for Farm and Country magazine. He has received six Canadian Farm Writers' Federation awards for journalism excellence. He's also worked for two of Canada's leading agricultural communications firms, providing public relations, branding and strategic marketing. Bern also works for Guelph-based Synthesis Agri-Food Network and talks the Real Dirt on Farming.

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