Soybean gall midge is a new species, identified in 2018, that is causing significant injury to soybean fields in five Midwestern states. As the 2020 growing season comes to a close, it’s apparent the severity of field injury from this new pest varied considerably over its known geographic range this year.

Of the five states, Nebraska appears to have had the greatest frequency and severity of infestations. All five states saw an expansion of this new pest to a total of 19 new counties in 2020, bringing the total to 114 counties. None of these new counties identified in 2020 had fields with significant plant injury, and only low levels of infestation were observed.

A number of counties in the east-central portion of Nebraska had a high frequency of infested fields, as well as a significant number of dead or dying plants along field borders. In late July through August, dead and dying plants were visible from the road in Otoe, Cass, Lancaster, Sarpy, Saunders, Dodge, Colfax and Platte counties.

In some cases, plant death exceeded 75% for up to 200 feet into soybean fields. In rare cases, injury was observed in the center of fields with infested and injured plants radiating from areas where plant establishment was poor. Significant infestations also were observed in northeast Nebraska in Stanton, Wayne, Thurston and Cedar counties.

This year's gall midge challenges

Several cultural, chemical and host plant resistant studies were conducted this summer. No tactics showed complete control, but it appears that some tactics were able to reduce the level of visible injury. Yield data from these studies is being collected and will be presented during the winter.

This year was particularly challenging for management because the long duration of adult emergence (an average of 25.6 days) from overwintering sites (last year’s soybean fields) meant that late planting dates in early June were not likely able to escape infestation. This duration was longer than in 2019, with an average of 16 days of adult emergence from overwintering sites.

The extended emergence in 2020 could be because of a dry, hot period in the midst of emergence. However, this is only a hypothesis, and more data will be needed to better understand the impact of environmental conditions on emergence.

INFESTED RANGE: Counties identified as infested with soybean gall midge from 2018 to 2020.

Newly identified counties (Jefferson, Saline, Polk, Merrick, Howard, Greeley and Boyd) in Nebraska showed no signs of wilting or dead plants, and the number of larvae on plants were low relative to fields in previously infested counties.

Larvae also were found on sweet clover in a number of counties across east-central Nebraska. Growers in these counties do not need to take any management actions in 2021, but they should monitor fields for injury and infestation.

General harvest recommendations

Many already are in the midst of harvest, and if you have been in soybean gall midge-injured fields, you may have seen varying levels of injury. Plant injury from soybean gall midge likely varies as a result of a number of factors, such as the time of infestation, plant development stage, number of larvae and environmental conditions.

Injured plants that survive the growing season often mature ahead of the majority of the crop and are at risk of releasing their seed from pods before harvest. In addition, weakened stems from larval feeding increase the likelihood that plants may lodge with heavy wind.

To reduce the likelihood of these losses, growers with significant field injury from soybean gall midge may want to consider harvesting infested field borders ahead of the rest of the field.

Postseason discussion plan

Several chemical, cultural and host plant resistance studies were conducted this year with some visual differences between treatments occurring during the season. An online event to present this information is being developed to update growers on the results from the season. Check soybeangallmidge.org for more information in the coming weeks.

McMechan is a Nebraska Extension crop protection and cropping systems specialist.