Managing yield potential and disease risk in lush soybean canopies

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It’s easy for growers to get excited in July when the rows close in their soybean crops and lush canopies are intercepting sunlight, generating high photosynthesis rates and building big yield potential.

But there could be trouble ahead if sclerotinia — the pathogen that influences white mould — infects flowers and allows the yield-robbing disease to gain a foothold in the field.

How can growers manage the crop, and that lush canopy, to best control white mould and minimize yield impact? Ontario Ministry of Agriculture, Food and Rural Affairs plant pathologist Albert Tenuta and University of Guelph associate professor David Hooker tackle the question in the 2021 Ontario Diagnostic Days video report, shown below.

Our diagnostic duo take a close look at lush soybean plots at Ridgetown campus and share how growers can manage crop canopy to better defend against the disease. Tenuta notes that some soybean varieties offer varying levels of tolerance to white mould but there is no true varietal resistance that can be counted on to defend the crop.

Tenuata say it’s important to know field history when building a white mould defence. If the field is susceptible, growers can help mitigate impact by adjusting seeding rates and plant populations. Hooker notes that row width choice is a critical decision for growers — white mould risk is much higher in narrow rows (7.5 inches) than wider rows (30 inches). Story continues after the video.

The researchers also break down fungicide strategies growers can employ to protect the crop. They note that humid, wet summer weather increases the likelihood of white mould development in dense growth canopies. In the report, Hooker discusses application timing noting that a first fungicide application should be targeted at the R2 stage — when a flower appears one of the upper two nodes.

Tenuta adds that it’s important to monitor the crop, weather and growing conditions to determine whether a second fungicide application is required — typically timed for R3 to R3.5. Fungicide efficacy research indicates that growers can expect a two to three-bushel return on a fungicide application and it certainly pays in a high-risk situation, he says.

Click here for more Ontario Diagnostic Days coverage.

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