
Editor’s note: This is part of a multi-part series that examines potential threats to 2024 crops and how to best manage them.
Corn farmers aren’t the only ones who need a halftime pep talk later this summer. Soybean farmers also need a halftime review, too. particularly when it comes to bean leaf beetles.
Farmers who planted soybeans before prolific late April and May rains particularly need to watch for these pests. They’re attracted to early-planted soybeans and can continue to infest them late into the growing season.
Thanks to the mainly mild winter of 2023-24, there’s lots of them out there. Statewide, the average Iowa mortality rate was 45% for the 2023-24 winter, according to Iowa State University entomologists. This was the lowest predicted mortality rate since 2012.
Bean leaf beetles can come in different colors ranging between yellow and green. “The one mark they all share is a small black triangle where the head meets the wings, says Jesse Grote, Syngenta agronomics services representative.
What to do
Bean leaf beetles often lie in host plants such as alfalfa, waiting to target early-planted soybeans. “As soon as the first soybean field opens up, that’s their dinner of choice,” Grote says. “They’ll start going after soybeans as soon as they begin cracking through the ground.”
Early-planted soybeans should be treated with an insecticide seed treatment with an effective mode of action, he says. Grote also advises also including a fungicide package. This is in the event bean leaf beetle injury spurs early-season soybean diseases and also to protect against soilborne seedling diseases.
“You’ll also want to scout fields in 15- to 20-foot increments across five areas in the field, and count the number of beetles per plant,” Grote says.
“When you’re scouting, be patient. If you’re making a lot of noise, they will fall off soybean plants and hide in a soil crack,” he adds.
A subsequent generation can also feed on pods and cause quality problems by serving as a vector for bean pod mottle virus and other pathogens. Thresholds for postemergence insecticide treatments can be found here.
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