Soybean Pests - Gall Midge

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Gall Midge - A New Pest of Soybean

Gall midge (also referred to as soybean gall midge or orange gall midge) is a relatively new pest of soybean.
Gall midge has been observed in soybeans for several years, but infestation levels and damage to soybeans have increased recently.
Little is currently known about this pest. It has been identified as belonging to the genus Resseliella, which includes 15 species in the U.S., none of which are known to infest soybeans. Genetic and morphological analyses conducted thus far suggest soybean gall midge is a likely new species (McMechan, 2018).
Research is ongoing to characterize the biology and lifecycle of this pest and develop management recommendations.

Gall Midge Species

The term midge is used to refer to a broad group of small fly species encompassing several taxonomic families.
Gall midge refers to species of flies in the family Cecidomyiidae. Gall midges are characterized by larvae that feed inside plant tissue, resulting in abnormal plant growth (galls).
Over 6,000 species of gall midge have been described worldwide, although the total number of species in existence is believed to be much larger. Over 1,100 species have been described in North America.
The gall midge family includes numerous species that are economically important pests of agricultural crops, including Hessian fly (Mayetiola destructor), wheat blossom midge (Sitodiplosis mosellana), and sunflower midge (Contarinia schulzi).
Some species of gall midge are known to feed primarily on decaying organic matter, fungi, and molds; therefore, they tend to be attracted to damaged or diseased areas on plants.

Field Observations in Soybeans

Gall midge damage in soybeans was first reported in Nebraska in 2011 in isolated cases mostly associated with damaged or diseased stems. Sporadic infestations were observed in subsequent years, but damage generally was not severe enough to impact yield.
Gall midge injury was first reported in South Dakota in 2015 and in western Iowa in 2016.
Pioneer agronomists and scientists at the University of Nebraska, Iowa State University, and South Dakota State University all noted increased infestation in 2018, with infestations occurring earlier in the season and causing higher levels of damage to soybeans.
Numerous infestations were observed in 2018 by Pioneer agronomists on otherwise healthy soybean plants, indicating that damaged or diseased tissue is not a necessary prerequisite for gall midge infestation.

Characteristics and Plant Injury

It is currently assumed that gall midge can overwinter in the Corn Belt as a pupa in the soil or crop residue and can complete at least two generations per year.
Adult midges are small (2-3 mm in length) and have long antennae and hairy wings.
Larvae are very small and start out white, turning bright red or orange as they mature (Figures 1-4).
Gall midge injury in soybean is a result of larval feeding, which occurs near the base of the plant. Multiple larvae can infest a plant.
Larvae feed inside the stem, causing swelling and abnormal growth (galls). Infested portions of the stem will appear swollen and brown (Figures 5-6).
Discolorations of the stem often begin near the soil surface and can extend up to the unifoliate node.
Prolonged feeding can cause the stem to eventually break off, resulting in plant death.

Injury Patterns in Soybeans

Infestation can occur during vegetative and reproductive stages.
Injury is generally most severe at field edges (Figures 7-8). Injury on field margins suggests fly movement from previous crop residue to new crop.
Injury has also been observed next to CRP and pastures, tree-lines, and groves.
In severe cases, infestation can extend into the interior of the field (Figure 9).
Depending on the severity of gall midge infestation, some soybean plants may wilt, die, or simply show signs of poor pod development and small seed size, especially in the upper 1/3 of the canopy on “healthy-appearing” green plants. Yield loss reports have ranged from a 1-2 bu/acre to nearly total yield loss depending on how early injury occurs and the severity of the infestation in certain areas of a field.

Management Considerations

Little is currently known about this pest and management recommendations are still in the process of being developed.
Preliminary investigations into foliar insecticide treatments have shown some promise for suppressing gall midge populations when applied at the time of pre-or early post-emergence herbicide applications to control egg-laying adults.
However, these types of insecticide applications still need more thorough evaluation, and careful consideration is needed to avoid insect resistance issues with midge or other insects, and potential harm to beneficial insects.
Foliar treatments later in the season when larvae feeding in the stems is already underway are not likely to be effective.
More insecticide treatment timings, active ingredients, and rates need to be fully evaluated to determine what options are effective.
Cultural practices and insecticide seed treatments do not appear to have an effect on the extent or severity of infestation.
Scouting recommendations for adult flies have not yet been developed. Scouting is likely to be challenging due to the small size of adult midges.

References

Hodgson, E. 2018. New Soybean Pest in Iowa: Soybean Gall Midge. Iowa State University. Integrated Crop Management News.
McMehan, J. 2018. Soybean Gall Midge: Adult Stage Identified. University of Nebraska-Lincoln Crop Watch.
McMehan, J., R. Wright, T. Hunt, and A. Nygren. 2018. Orange Gall Midge in Soybeans. University of Nebraska-Lincoln Crop Watch.
Varenhorst, A. and C. Strunk. 2015. Gall Midge Larvae in Soybean Stems. South Dakota State University.
Varenhorst, A., A. Bachmann, P. Rozeboom, and P. Wagner. 2018. Do You Have Gall Midges in Your Soybean? South Dakota State University.