Soybean School: Dry weather brings spider mites and aphids

From cereal aphids to armyworm, Ontario growers have already seen significant pest pressure in 2020 crops and there’s more on the way.

As the calendar turns to July and hot, dry conditions persist, soybean growers need to be on the lookout for both spider mites and aphids in their crops, says Ontario Agriculture, Food and Rural Affairs field entomologist Tracey Baute.

On this episode of RealAgriculture Soybean School, Baute explains that with wheat harvest fast approaching, mites will now be looking for a new home and will be seeking out soybean and edible bean fields.

Spider mite damage can typically be identified by stippling on the upper surface of the leaf; plants often look sandblasted and webbing can appear on the underside of the leaf. Baute notes that in dry years, many growers confuse the symptoms with drought stress: “sometimes if those symptoms are visible in the field, you’re almost too late.”

But there are control options. She advises growers to keep a sharp eye on field edges and turn over leaves, especially in the mid and lower canopy. A hand lens may be required to spot the tiny dots moving around and if pressure is above threshold — four mites per leaflet — spraying is an option to reduce yield impact. (Story continues after the video.)

Baute is also anticipating the return of soybean aphids, a very sporadic pest in recent years. In the video, she notes the important role biological controls and beneficial insects play in controlling this pest. She recommends growers and agronomists who have little experience with soybean aphids should utilize the Aphid Advisor app.

Baute advises growers to scout fields multiple times from the R1 to R6 stage while using the app. She explains how the app uses established thresholds, the level of natural enemies in the field, and the rate of aphid population increase to make spraying recommendations.

Click here for more Soybean School videos.

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