Soybean School: Bean leaf beetle making a comeback


Many Ontario farmers will remember when they routinely sprayed soybean crops to control bean leaf beetle. That changed 10 years ago with the introduction of neonicotinoid insecticide seed treatments, which helped suppress populations of the pest in Ontario and many U.S. states.

But the pest is mounting a comeback as neonic use continues to decline and many growers opt to plant seed treated with just fungicide. “About 10 years ago with the area-wide use of neonic seed treatments we actually saw a population suppression of bean leaf beetle,” says Ontario Ministry of Agriculture, Food and Rural Affairs field crop entomologist Tracey Baute.

Baute has seen increasing populations of the pest this spring and is urging growers to get out and scout their fields for the beetle, which is most often identifiable by the black triangle just behind the neck region. In this episode of RealAgriculture’s Soybean School, Baute discusses what growers should be looking for when they scout their fields, thresholds and how to access neonics to help control the pest.

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  • When scouting fields, growers need to keep an eye out for bean leaf beetles. Baute says there are insecticide spraying options if pests exceed threshold: “From VC to V2, if you find 16 beetles per foot of row you have reached threshold.”
  • Beyond V2 there is a defoliation threshold up to bloom which is set at 30 percent. “But I just can’t predict what will happen this year because it’s the first time we are seeing more presence again,” adds Baute. “It’s just a matter of watching and spraying if you need to.”
  • Baute also notes that it’s important to scout and assess thresholds if growers want to use a neonic insecticide seed treatment next year. “This option is available if they find that they have a significant stand loss. That doesn’t mean the plant has to be completely gone. It just has to be injured.”
  • To get neonic use approval, based on Ontario guidelines, Baute says growers need to have a crop inspection done by a certified professional pest advisor. They will assess the stand and determine if it exceeds the neonic threshold which is 15 percent stand loss in corn fields and 30 percent in soybeans for both bean leaf beetle and seed corn maggot. “That gives you permission or access to neonics for your entire farm property for the next 12 months after your assessment – that is an available option if you start to see injury.”

Click here for more Soybean School episodes.

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