Soybean Gall Midge Brings More Questions Than Answers
In 2018, small orange midge larvae were found, causing significant injury and yield loss to soybean fields in Nebraska, Iowa and South Dakota as well as in several Minnesota counties. In the two years following this larvae’s discovery, the areas affected by soybean gall midge continue to increase, although the number of affected acres is still quite minimal.
While the pest does not yet pose a national threat, it has raised important questions on mitigation and management best practices. Here are five important things to know about soybean gall midge as you assess your pest management plan this season.
1. The highest soybean gall midge infection rate is within high grass areas.
Gall midge starts as a fly, which then lays an egg. Infection happens when that egg hatches in a soybean. These flies tend to live in tall grass areas, like road ditches or the outside edges of a field.1 If you notice that the outer rows of your field are having trouble growing, reach out to your agronomist to verify if you have gall midge pressure. Stem breakage, dark lesions, or wilted or dead plants are all additional signs that this insect may be affecting your crops.
2. Severe soybean gall midge pressure can cut off nutrient flow.
The gall midge enters the plant stem a couple of inches above the soil surface. As the midge increases in size, it will ultimately stop the flow of xylem (the tissue that transports water and minerals from roots to stems and leaves) and phloem (the tissue that transports sugars throughout the plant), cutting off nutrient flow and causing the plant to starve and die.
3. Soybean gall midge control is a mystery.
Once a soybean midge is inside the plant stem, spraying a foliar insecticide is much less effective because the insect is somewhat protected. It’s not on the outside of the leaves like a soybean aphid would be, so it won’t come into direct contact with the spray. At this point, we don’t have an answer about how to try to prevent it, and there aren’t any reported incidences of genetic tolerance or resistance to it.
4. There appears to be a link to white mold.
According to an article from the University of Minnesota Extension, gall midge larvae found in Minnesota were most often associated with Sclerotinia white mold.2 This makes sense, since the sclerotia bodies sprout the mushrooms — or apothecia — of a white mold. These apothecia then release fungal spores, which usually enter the soybean plant through a dead, dying or decaying flower. If there’s a fly that’s poking its stylet into the stem of the soybean plant to lay an egg, that tiny hole could provide enough of an opening to allow a fungal spore to enter the plant.
Another scenario is that as the gall midge grows larger in the stem, it appears to crack the stem open. This would also present an open door for white mold fungal spores to enter the plant and infect it with this disease.
5. Insects tend to travel frequently.
Besides laying many eggs during their life cycles, on the whole, insects move around and test out different regions because of competition for food. Since they reproduce so rapidly, they can quickly adapt to environmental changes, whether that’s colder winters, wetter summers, or hotter and drier conditions. This may explain why insects like soybean gall midge are moving throughout the Midwest.
If you find soybean gall midge, contact your agronomist. He or she can steer you to other resources or experts to report the problem to and determine if further consultation is needed.
1. McMechan, J. Winfield United Minnesota Regional Conference. University of Nebraska. February 2020.
2. Potter B, Koch B. Update on soybean gall midge: A new pest of Minnesota soybean. University of Minnesota Extension, Minnesota Crop News. June 6, 2019. https://blog-crop-news.extension.umn.edu/2019/06/update-on-soybean-gall-midge-new-pest.html
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