Soybean Gall Midges are Emerging, Start Scouting Soon

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Soybean Gall Midges are Emerging, Start Scouting Soon

Figure 1. Soybean gall midge mature (dark orange) and young (clear to light orange) larvae on soybean stems. (Source: E. Hodgson. ISU)
  • The soybean gall midge continues to spread and is currently observed in Nebraska, Iowa, South Dakota, Minnesota, and Missouri 

  • Adult emergence has been detected in several regions over the past 14 days 

  • Scouting for larvae and damage should start on field edges  

  • Damage by gall midge may look similar to that caused by other pathogens and pests 

The soybean gall midge (SGM) is an emerging pest of soybeans in parts of the Midwest, being first reported in Nebraska in 2011. Since then, the presence of the SGM continued to expand and to date, this pest has been confirmed across Nebraska, South Dakota, Iowa, Minnesota, and Missouri. Severe damage by SGM can lead to significant stand and yield losses. Over the last two weeks there have been increasing reports of adult emergence. Consequently, we can expect to observe SGM larvae and their activities starting in these areas soon. A good way to stay on top of SGM is to visit the soybean gall midge alert network and sign up for alerts. The network is located at https://soybeangallmidge.org/ - scroll to the bottom of the page to sign up for alerts.  

 

Pest Description and Damage 

The soybean gall midge (Order Diptera, Family Cecidomyiidae) is a small fly in the genus Resseliella; R. maxima. The larval (maggot) stage is legless, orange in color when mature, while young larvae are clear to white and smaller in size (Image 1). The adults are about ¼” long, slender, with an orange abdomen and long legs showing a white and black banding on them. Adults emerge primarily from previously affected soybean fields, where they mate and lay eggs in existing soybean fields and potentially other hosts such as alfalfa and sweet clover. Since 2019, adult emergence has occurred from late May through mid-June in many regions. Adult emergence can last for several weeks, and there appears to be at least two generations of the pest that may overlap over the course of the season. After mating, adult females lay eggs that hatch into maggots within six days. Observations indicate that damaged soybeans (those damaged by hail or contain fissures/cracks on the stem) are favorable for SGM egg laying. Maggots feed within the stem, damaging the vasculature and potentially leading to plant death or lodging.  

Several SGM maggots can be found feeding in one soybean stem. Symptoms of damage to soybeans include dark discoloration or swollen stems at the soil surface. The outer layers of the stem can be peeled back and reveal the clear to orange-colored larvae feeding on the stem. Damage tends to be most severe on field edges. Data from Nebraska, on a small-scale sample, showed up to 100% yield loss in the first 100 ft from the field edge and about 20% yield loss 200 and 400 ft from the field edge. High numbers of dead plants will negatively affect yields and even when plants survive, weakened stems are more prone to lodging. Aboveground symptoms could be misdiagnosed as seedling and stem pathogens (Phytophthora, Pythium, stem canker, red crown rot) especially if the weather and soil conditions are ideal for disease development. However, if the SGM is the cause, closer examination of the stems should reveal the presence of the larvae.  

 

What do we know so far? 

Researchers in states affected by the SGM have gathered as much information as possible and continue to study this pest, its biology, and effective ways to manage it. There is much that we still do not know about this pest, its biology, and how to manage it. 

 

How about chemical controls?  

Contact insecticides will not provide control of the larvae as they are “protected” from encountering the chemical once inside the stem. The prolonged emergence period of adults, in addition to the overlapping generations, makes controlling this pest with foliar products extremely challenging. Research on the efficacy and effectiveness of foliar applied insecticides is ongoing, though some products, such as Endigo(R) have 2ee labels for SGM suppression in some states. High rates of seed treatments and systemic insecticides have shown highly variable and inconsistent results. Planting date has not been demonstrated to have a significant impact on SGM, though earlier plantings tend to have more SGM larvae than later plantings. Additional work on cultivar tolerance or resistance and other practices such as hilling and tillage are ongoing.  

 

The best way to stay up to date on SGM is to sign up for alerts at the soybean gall midge network, as mentioned previously.  

 

Figure 2. Adult soybean gall midges. (Source: Mitchell Helton, ISU)


Sources: 
Justin McMechan. Soybean Gall Midge. Cropwatch publications 2018-2021. University of Nebraska-Lincoln. https://cropwatch.unl.edu/gallmidge
Erin Hodgson and Ashley Dean. Soybean gall midge: A new field crop pest. 2018. Iowa State University. https://store.extension.iastate.edu
 

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