A farmer checking on another problem in his soybean field found a plant here and there with a few round holes in one or more leaves. He wondered what caused it, and he wondered if it was anything to worry about.
John Obermeyer, Purdue University Extension entomologist, says the answer is pretty straight forward. The holes are most likely due to bean leaf beetle feeding. When overwintering, bean leaf beetles emerge and they look for food.
"It isn't anything to worry about," he says. "I would be surprised if I walked through a soybean field and didn't find a few small holes in leaves here and there."
Several seed treatments supplied on seed control bean leaf beetles. However, the insects have to take a bite of leaf to ingest it, so there will still be some holes.
"Seed treatment insecticides are effective against these beetles, but that doesn't mean anything at harvest," he insists. "There isn't going to be any yield loss from spotty, early feeding anyway."
Obermeyer says soybeans would have to lose half or more of their leaf surface area to feeding by insects at the early stage shortly after emergence before it would be an issue worth worrying about. He hasn't heard reports of any feeding near that level.
"Actually things have been quiet so far this spring," he says. "We just haven't heard about anything out of the usual, or anything in the insect and crop world to get excited about."
The first generation of bean leaf beetles emerging from eggs laid now will show up later in July, he says. Usually they're not a large cause for concern either. If bean leaf beetles are going to be a problem and perhaps threatened yield, it likely wouldn't happen until very late in the season when the second generation emerges.
"Then the issue is whether they feed on pods in significant numbers to cause an economic problem," he says.
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