NDSU Extension - Griggs County

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December 18

The Extension Connection Column by Jeff Stachler

 

Soybean Gall Midge – A New Soybean Insect About to Reach North Dakota

Good Friday to you!  Merry Christmas to all of you!  The holiday season is upon us.

I would ask that all farmers take the time to call the office or stop by the office to introduce yourself to me and provide me with your phone number(s), address, and e-mail address.  I would like to get a list of correct e-mail addresses and start an Agriculture Newsletter.

I would also like to start a rainfall and snowfall record for the county.  If you measure every snowfall and rainfall on a daily basis, I would love it if you would call me and let me know.  I think it would be great to keep track of local precipitation.  There is even a nationwide official precipitation recording organization in the United States called CoCoRaHS.  If you want to participate in the official program let me know and it would cost you the fee for the special rain gauge.  I just set mine up at my house this past weekend.

A new soybean insect pest is knocking at the door of the North Dakota and South Dakota and Minnesota borders!  It is called the soybean gall midge and is a Dipteran or fly.  It was first detected in the United States in some isolated areas of a Nebraska soybean field in 2011.  By 2018 it was reported as a severe problem in many fields in Iowa, Nebraska, and South Dakota and first found in Minnesota.  Since then it was also found in Missouri. 

The soybean gall midge has two to three generations per season.  The first generation adults emerge in mid-June in Nebraska.  The adults breed and live for only a few days.  The eggs are laid and the larvae feed on the base of the stem molting into three instar stages.  The first two stages the larvae are white in color, but in the last stage the larvae are orange in color.  The last generation of larvae produce cocoons or advance to the pupa stage to survive the winter.

Symptoms include wilting plants, a dark discoloration at the base of the plant that can be swollen, and maybe even dead plants.  To see the larvae peel back the outer epidermis.

This pest is a field edge (perimeter) problem although it can move fairly far into the field by the end of the season.  It will always be most severe along the first 100 feet of the field.  They have detected between 20% yield loss near the center of the field and up to 100% yield loss on the field perimeter!

Control is difficult.  One cultural strategy is to rotate away from soybeans.  If you grow continuous soybeans, they only get worse.  One strategy that helps in Nebraska is to wait to plant soybeans until June 1st to 15th, but that is not very realistic for our area.  The earlier soybeans are planted the worse the problem will get for the season.

Insecticide control is difficult.  Insecticide seed treatments have only been marginally effective on the first generation only.  Foliar insecticides can be used when the adults emerge, but they have only been about 50% effective.  More work is necessary to make insecticide control more effective.

There is another gall midge currently present in southeast North Dakota.  It is called the white mold gall midge and looks very similar to the soybean gall midge.  Therefore we are concerned the soybean gall midge will be mis-identified.  Fortunately it is not an economic pest as it feeds on the white mold on the soybean plant and other species.

The larvae look very similar to each other, although the soybean gall midge can be more reddish-orange.  There are markings on the adults that make it possible to separate them.  One great way to tell the difference is when and where you find them.  The soybean gall midge can be seen as early as the V3 (third trifoliate) stage and on the field perimeter while the white mold gall midge comes in after flowering when white mold starts to develop and will be in parts of the field with white mold.

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