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New insect pests create soybean concerns

leafminer adult has tiger-like stripes and a furry-looking tail. Larvae looks yellow and transparent and like a gummi worm
Leafminer adult and larva

Soybean farmers have been asked to keep an eye out for a pest that was found for the first time in Minnesota soybean fields in 2021. According to Robert Koch, University of Minnesota Extension entomologist, the leafmining caterpillar called Macrosaccus morrisella is a small insect, with larvae reaching less than 5 millimeters and adults only slightly larger.

This leafminer is native to the U.S. and was previously known to only feed on two plants: the American hog peanut and the slickseed fuzzybean, so it has sometimes been called the hog-peanut leaf miner. But now there is concern for soybean plants.

diagnostic photos show the white blotchy leafmines.
Leafminer damage on soybean

On soybeans, injury from the pest can be detected on the lower surface of the leaves as white blotchy leaf mines.

The impact of this leafminer on Minnesota soybean fields remains unknown, according to Koch. He says those who spot the leaf miner should contact him directly because he is conducting early-stage research to assess the potential for damage and spread.

Koch has an appointment as an associate professor in the University’s College of Food, Agricultural and Natural Resource Sciences. His dual roles as faculty researcher and Extension specialist, along with the statewide network of Extension educators and collaborators, helps ensure that research meets the needs of Minnesota farmers.

Soybean gall midge

Tiny bright orange larva
Soybean gall midge larvae

Another insect pest that is relatively new to Minnesota is the soybean gall midge. Entomologists are only beginning to understand the midge’s biology. The midge’s larvae are believed to overwinter inside cocoons in the soil of infested soybean fields, with adult emergence beginning in June.

Bruce Potter, an Extension specialist in integrated pest management, says there are no recommendations for the management of soybean gall midge in Minnesota yet. Seed-applied insecticides don’t appear to be effective and more research is needed on foliar application. Potter says it’s possible soybean varieties resistant to soybean gall midge could be developed and might be a valuable management tool in the future.

Digital Crop Doc

University of Minnesota Extension’s crops team is using technology to help Minnesota farmers more quickly identify plant diseases that may develop in their fields. The team has developed Digital Crop Doc  a new program farmers can use to help diagnose diseases in corn, soybeans, small grains, sugar beets and forages.

Growers are asked to fill out an online form and submit photos of their diseased plants. A crops team member will then contact the farmer with a diagnosis, a request for more information or possibly a suggestion to submit plant samples to the University’s plant disease clinic.

There is no cost to use Digital Crops Doc. Submissions will help alert the crops team to new or emerging crop diseases across the state.

Related topics: Featured news Source Fall 2022
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