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Research Highlights

Research Highlights
Soybean gall midge: Research focus on economic pest and how to combat it

By Scott Nelson, Iowa Soybean Association On-Farm Network® Director

The gall midge has become an economic pest of soybeans in Iowa and beyond. It was found in soybeans in the western third of Iowa, eastern Nebraska and eastern South Dakota. Farmers were encouraged to look for symptoms but no pests were reported in central or eastern Iowa. 

The gall midge is a small fly, about 1/16th of an inch in size. It is characterized by hairy wings, long legs and a long ovipositor. There are many species of midges, and the soybean gall midge adult is difficult to identify even by expert entomologists. 

Currently, not much is known about the insect, but scientists are actively researching and reporting what they’ve learned so far. 

The first recognition of the pest was in eastern Nebraska in 2011. In 2015, it was found in northwest Iowa, eastern South Dakota and eastern Nebraska. Gall midge populations increased in 2016 to the point of significant soybean yield reductions. The pest grew in intensity in 2017 and became widespread in 2018. 

Soybean gall midge larvae

Gall midge adults have been found on yellow sticky card traps in soybean fields, but entomologists prefer to use emergence cages to collect adult flies. It is important to note that while the adult gall midge does not feed on soybeans, the orange-colored larvae feed on the soybean stems, causing severe destruction and often whole plant death. 

Scientists believe the life cycle of the gall midge is as follows: 

  • Larvae overwinter in the soil. 
  • After pupation in the early spring, adult midges emerge and lay their eggs at the base or lower stems of soybean plants. 
  • The eggs hatch and the larvae feed on the stems. Based upon observations, there appears to be two to three overlapping generations per year. 
  • For the hessian fly, a cousin of soybean gall midge, the life cycle from egg to adult is about four weeks. In some observations, the first generation of soybean gall midges were found on 3-inch soybeans. 

No consistent patterns in planting dates, crop varieties, presence of cover crops, tillage or row spacing have been found that affect the insects’ population growth or decline. 

Insecticide seed treatments have not shown to be effective. Some researchers believe that higher rates of insecticide seed treatment could offer some suppression. However, these high rates of seed treatment are not currently offered and there is no scientific data to support their effectiveness. Some farmers observed that fields treated with a foliar insecticide had a lower incidence of soybean gall midge, but this has not been verified in controlled studies.  

Over the next several months, entomologists and crop protection professionals will be diligently working on potential solutions for 2019 production. Although not proven, the following are some points to consider for control of gall midge in future production: 

  • Monitor for presence of the fly the first four to eight weeks after planting. This can be done with sticky traps or emergence cages. The fly is difficult to identify and will require use of a hand lens and a detailed guide on how to identify the pest. This guide will be produced before spring 2019. 
  • As soon as soybean gall midge adults are identified, apply a foliar contact insecticide. Since adults do not feed on soybean plants, longer lasting residual insecticides are not necessary. Place applications on field edges, as the midge attacks here first. 
  • The hope is that a single foliar application of insecticide could provide sufficient suppression of soybean gall midge. However, it may be necessary to do two applications. 
  • Entomologists do not think that insecticides have any effect on the larvae, as they feed inside the soybean stems. Control options must be focused on adult flies. 

Not all foliar insecticide labels will allow for application to control the soybean midge. Researchers and insect experts are working with crop protection companies to develop emergency use labels on insecticides that could have suppressive activity of the pest. 

Some of the 2019 Iowa research includes insecticide efficacy in one- and two-pass programs as well as for higher rates of seed treatment.  

Read more about researchers are learning about the soybean gall midge in the resource library.

Other resources: Update on Checkoff-funded Research on Soybean Gall Midge – a New Soybean Pest