- DTN Headline News
Pests of the Week
Monday, June 24, 2019 10:30AM CDT
By Emily Unglesbee
DTN Staff Reporter

ROCKVILLE, Md. (DTN) -- Only about half of the country's soybeans have emerged, but some insect pests are already out and about, waiting for them.

Entomologists and agronomists have reported sightings of soybean aphids, bean leaf beetles and even the soybean gall midge -- a new pest of soybeans that emerged last year.

Scout early and often, and don't neglect those early-planted soybean fields that are further along, cautioned Jim Donnelly, a technical agronomist for DeKalb and Asgrow in Illinois. Some of them may be the only available soybean foliage in a landscape of late-planted or prevented planting fields, which makes them a magnet for soybean insects.

"Never let your guard down," he said. "My recommendation is -- regardless of the insect management strategy you have -- to always be out there looking."


Even with very few soybean fields up and growing in his region, Donnelly has already spotted some soybean aphids in northern Illinois.

Farther north, University of Minnesota IPM specialist Bruce Potter announced his team's first sighting on June 7. Aphids overwinter on buckthorn each year, and Potter suspects volunteer soybeans may have helped populations along this year, too.

"In many fields, volunteer soybeans are numerous this spring," he wrote in a university newsletter. "Depending on herbicide tolerance of the previous year's soybean crop and corn herbicide selection, these volunteers can persist in corn. MN Soybean Checkoff-funded research has shown that when colonized, volunteer plants in corn can produce significant numbers of SBA to move to soybean fields later."

Scout your emerged soybeans frequently for this pest, which is capable of population explosions when conditions are right, Donnelly noted. They like moderate temperatures and dry weather, Potter said.

Remember that it takes very large populations to cause damage, and that insecticides will also knock down the population of beneficial insect predators like lady bugs. The threshold for treatment through the R5 growth stage is more than 250 aphids per plant, with 80% of plants infested and populations increasing.

Overtreatment has helped produce some pyrethroid-resistant aphid populations in Minnesota. See more on that problem and aphid management from the University of Minnesota here: https://extension.umn.edu/…. See Potter's article here: https://swroc.cfans.umn.edu/….


Bean leaf beetles are also active. Donnelly has spied some feeding, as have entomologists in Wisconsin and Kansas.

"We've seen some bean leaf beetle injury, especially in fields that were planted really early and fields that didn't have insecticide treatments on the seed," Donnelly said. "That's fairly typical."

The adult beetles have black markings overlaid on their yellow, orange or even reddish backs -- and they love young, emerging soybeans. They will happily feed on cotyledons, stems and leaves, creating distinct round holes and gaps. Later in the season, pods can be a more damaging target.

The good news is that soybean seed treatments can provide good protection against their early season feeding, and soybean plants can bounce back from their defoliation, noted Kansas State Extension entomologist Jeff Whitworth. "Remember, these young plants are very resilient at overcoming up to about 50% defoliation in these early vegetative stages," he wrote in a university pest newsletter.

However, the bean leaf beetle also serves as a vector for the damaging bean pod mottle virus. See more details on bean leaf beetle and bean pod mottle virus here: https://crops.extension.iastate.edu/…. You can find information on managing the pest and treatment thresholds here: https://www.pioneer.com/…. See Whitworth's article here: https://entomology.k-state.edu/….


The soybean gall midge caught everyone off guard last year -- scientists, farmers and industry. The midge larvae were discovered tunneling their way through soybean stems and causing economic damage on field edges in Iowa, Nebraska, Minnesota and South Dakota.

"By the way it was moving last summer, it seems like it's only a matter of time until it's here," Donnelly said of Illinois. "We're definitely watching for it."

This year, Iowa State University scientists found the first gall midge adult flies on June 14 in northwest Iowa, in a field that had been infested with the insect last year. The scientists will continue trapping and alert growers to the best time to treat.

"At this point, just a few individuals in traps does not warrant a foliar insecticide," wrote Iowa State University Extension entomologist Erin Hodgson. "But our plans are to make treatments when adult captures increase. We will be sure to keep you updated on subsequent detections and application recommendations in the future."

The gall midge damage began in June last year, when farmers noticed wilting soybean plants, with swollen, sometimes broken, stems. Inside, they found the tiny midge larvae, ranging in color from pale and clear to bright orange. Scientists are still getting up to speed on the pest, but it seems to do its worst damage on field edges and at the base of soybean plants.

Growers who had gall midge infestations in their fields or state last year should watch their soybeans carefully.

"This insect, and its potential for damage, may be widespread in Minnesota," Potter and UM Extension entomologist Bob Koch said in a recent university news alert. "During 2019, look for damage from the larvae. Look for wilting soybean plants, particularly on field edges adjacent to 2018 soybeans. Peel back the soybean stem epidermis and split stems to look for the small white to orange larvae."

See the Minnesota news alert here: https://blog-crop-news.extension.umn.edu/….

See the Iowa State 2019 gall midge finding here: https://crops.extension.iastate.edu/….

See some of DTN's previous coverage of this new pest here: https://www.dtnpf.com/… and here: https://www.dtnpf.com/….

Emily Unglesbee can be reached at Emily.unglesbee@dtn.com

Follow her on Twitter @Emily_Unglesbee


blog iconDTN Blogs & Forums
Technically Speaking
Editorial Staff
Monday, June 24, 2019 10:49AM CDT
Monday, June 17, 2019 10:27AM CDT
Monday, June 10, 2019 12:00PM CDT
Fundamentally Speaking
Joel Karlin
DTN Contributing Analyst
Monday, June 24, 2019 10:50AM CDT
Thursday, June 20, 2019 11:07AM CDT
Wednesday, June 12, 2019 12:13PM CDT
DTN Ag Policy Blog
Chris Clayton
DTN Ag Policy Editor
Monday, June 24, 2019 4:19PM CDT
Thursday, June 20, 2019 3:04PM CDT
Wednesday, June 19, 2019 3:38PM CDT
Minding Ag's Business
Katie Behlinger
Farm Business Editor
Wednesday, June 5, 2019 11:34AM CDT
Tuesday, May 28, 2019 3:02PM CDT
Monday, May 20, 2019 10:16AM CDT
DTN Ag Weather Forum
Bryce Anderson
DTN Ag Meteorologist and DTN Analyst
Monday, June 24, 2019 8:25AM CDT
Friday, June 21, 2019 10:24AM CDT
Wednesday, June 19, 2019 1:05PM CDT
DTN Production Blog
Pam Smith
Crops Technology Editor
Thursday, June 13, 2019 4:47PM CDT
Thursday, June 6, 2019 5:22PM CDT
Friday, May 31, 2019 4:49PM CDT
Harrington's Sort & Cull
John Harrington
DTN Livestock Analyst
Tuesday, June 11, 2019 3:25PM CDT
Thursday, June 6, 2019 12:26PM CDT
Tuesday, April 16, 2019 11:17AM CDT
South America Calling
Editorial Staff
Tuesday, April 23, 2019 2:43PM CDT
Tuesday, April 9, 2019 2:22PM CDT
Wednesday, April 3, 2019 5:24PM CDT
An Urban’s Rural View
Urban Lehner
Editor Emeritus
Wednesday, June 19, 2019 6:36PM CDT
Tuesday, June 11, 2019 6:35PM CDT
Monday, June 3, 2019 3:28PM CDT
Machinery Chatter
Dan Miller
Progressive Farmer Senior Editor
Friday, June 14, 2019 3:53PM CDT
Friday, May 31, 2019 12:50PM CDT
Wednesday, May 22, 2019 12:56PM CDT
Canadian Markets
Cliff Jamieson
Canadian Grains Analyst
Monday, June 24, 2019 3:39PM CDT
Friday, June 21, 2019 4:00PM CDT
Thursday, June 20, 2019 5:29PM CDT
Editor’s Notebook
Greg D. Horstmeier
DTN Editor-in-Chief
Wednesday, May 1, 2019 5:59PM CDT
Thursday, April 25, 2019 8:51AM CDT
Thursday, April 11, 2019 8:29PM CDT
Copyright DTN. All rights reserved. Disclaimer.
Powered By DTN