Since late June, orange gall midge (also known as soybean gall midge) (Figure 1) has shown up in a number of soybean fields in eastern Nebraska. This insect was first reported in Nebraska in 2011 and has was initially considered as a secondary pest of soybeans, occurring on previously damaged or disease-comprised soybean plants. This year it showed up much earlier than in previous years. The field distribution of plant damage, number of maggot per soybean plant, and absence of disease in some cases has raised concerns about its status as a pest. For more information on symptoms see the August 1 CropWatch article.

Over the past few weeks, scattered reports have come in from fields in a number of counties in eastern Nebraska. As a result, a survey was initiated to determine the distribution and extent of symptomology in soybean fields. Fields were sampled at random approximately every 10 miles in counties with no reports of field issues. If a field showed symptoms of dead or dying plants, it was investigated for the presence of the maggot (Figures 2 and 3).

Counties highlighted as blue or orange in Figure 4 indicate the presence of the maggots in fields. Orange counties are areas where field symptoms of dead plants were readily observed from the road. Of all the counties sampled, only two (Gage and Pawnee) had no orange gall midge. Each field in the survey was sampled at 10, 20, 50, 100, and 400 feet from the field edge. Heavily damage fields had plant death in excess of 30% at 400 feet, with nearly all surviving plants infested with maggots.

A number of observations were made through the survey. In many cases, heavily damaged fields were adjacent to corn fields that had been planted to soybeans the previous year. Distribution of damage from the field edge was also commonly associated with uncut bromegrass. Bromegrass may serve as a suitable mating site for the adults. Such information is purely observational, and research is underway to understand what factors might increase the risk of orange gall midge infestation and damage to soybean.

Most of the soybean crops in Nebraska are in the late R5 to R6 stage. As we near harvest, we recommend growers prioritize harvest of damaged fields due to the increased risk of lodging because of weakened stems.

If you have observed orange gall midge maggots in your county and it is not highlighted on the map, please contact Justin McMechan at justin.mcmechan@unl.edu.