Wallaces Farmer

Meet the (bean leaf) beetles

They particularly target early-planted soybeans.

Gil Gullickson, editor of Wallaces Farmer

May 24, 2024

2 Min Read
Bean leaf beetle on leaf
BEWARE, EARLY-PLANTED BEANS: Bean leaf beetles target early-planted soybeans, often first lying in host plants such as alfalfa before moving in. Courtesy of Syngenta

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.

About the Author(s)

Gil Gullickson

editor of Wallaces Farmer, Farm Progress

Gil Gullickson grew up on a farm that he now owns near Langford, S.D., and graduated with an agronomy degree from South Dakota State University. Earlier in his career, he spent 13 years as a Farm Progress editor, covering Minnesota and the Dakotas.

Gullickson is a widely respected and decorated ag journalist, earning the Agricultural Communicators Network writing award for Writer of the Year three times, and winning Story of the Year four times. He is a past winner of the International Federation of Agricultural Journalists’ Food and Agriculture Organization Award for Food Security. He has served as president of both ACN and the North American Agricultural Journalists.

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