New Soybean Pests: Gall Midge and Tentiform Leaf Miner

It’s hard enough dealing with long-standing pests, but it’s even more overwhelming to add new pests to the lineup, namely gall midge and tentiform leaf miner.

But don’t let these new pests cause undue stress. We’ve done the heavy lifting and put together a brief overview of which locations are affected, signs of damage to watch for and the economic impact of potential yield loss from these pests.

Soybean gall midge

Soybean gall midge was initially discovered in 2011, and in 2018 it was identified as a new genus. Until 2018, midge infestations had been considered secondary—i.e., they targeted injury sites on plants that had already been harmed by weather damage or disease. However, beginning in 2018, gall midge infestations were detected earlier in the season and in higher numbers, even on plants without previous injury or disease.¹

Gall midge primarily affects Nebraska, Iowa, South Dakota, Minnesota and Missouri.²

Infection spreads along field edges at first and typically causes higher yield reduction in those areas. Researchers found that in small samples of heavily damaged fields there was complete yield loss from the edges of the field up to 100', whereas 200' and 400' from the field edge only experienced 20% yield loss.³

Soybean gall midge damage

Gall midge larvae feed on the lower stem and tissues at the base of the soybean plant, critically disrupting the flow of nutrients and water within the plant. Adult gall midge does not feed on soybean plants.

Soybean gall midge symptoms

Initial symptoms of gall midge look similar to the damage caused by fungal pathogens like Phytophthora and Rhizoctonia. First symptoms include discolorations and dark lesions on soybean stems near the soil line. Stems subsequently weaken and wither, eventually causing breakage at the base. Heavy infestations will cause soybean plants to wilt and die.

Soybean gall midge control

Researchers understand that controlling this pest will require accurate insecticide timing. But unfortunately, gall midge is currently hard to suppress as they are well protected inside the soybean stem, with no research-based, effective management tactics established.
Universities are working to evaluate insecticides (soil-applied and foliar-applied seed treatments) as well as soybean genetics that may help growers find solutions. Cultural tactics may be beneficial to reduce yield loss as well. This includes using practices like avoiding planted near infested fields and removing weeds that act as a food source to leafminers.

Soybean tentiform leafminer

Discovered in 2021 in Minnesota, soybean tentiform leafminer is now affecting Minnesota, North Dakota and South Dakota.
Similar to gall midge, soybean tentiform leafminer typically infests soybean crops along field edges or near wooded areas.⁴

Tentiform leafminer damage

The larvae of the tentiform leafminer feed inside the soybean leaves, forming mines between midribs and main lateral veins. This mined tissue subsequently dies, reducing leaf area and causing damage similar to defoliation.
Research to determine yield loss specifically from leafminer has yet to be completed, but defoliation thresholds can act as a reference point for predicting yield loss. For soybeans, defoliation thresholds currently sit at 30% during vegetative soybean growth stages and 20% during reproductive stages.⁵

Tentiform leafminer symptoms

Tentiform leafminer larvae are responsible for creating damage to soybean plants. Larvae feed inside leaves, hollowing out leaf tissue and forming mines that are visible on the lower surface of the leaf. As the infestation continues, mines are visible on the upper surface as a tentiform mine is created, causing the upper leaf surface to buckle up. These mines impact yield by reducing photosynthetic area similar to other defoliating pests and disease.

Tentiform leafminer management

Insecticide efficacy and application timing has yet to be thoroughly investigated for the tentiform leafminer. With more research, foliar application of insecticides may work to control this pest.

Experts are available to help you make your decisions. Reach out to your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative.

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Endnotes

1. Tilmon, Kelley, and Douglas J. Jardine. “Soybean Gall Midge” Soybean Research & Information Network, 11 June 2020, soybeanresearchinfo.com/soybean-pest/soybean-gall-midge/. Accessed 20 Oct. 2024.
2. Green, Jody. “Soybean Gall Midge: Discovery of a Delicate and Destructive New Species.” Entomology Today, 16 June 2021, entomologytoday.org/2021/03/09/soybean-gall-midge-delicate-destructive-new-species-integrated-pest-management/. Accessed 20 Oct. 2024.
3. McMechan, Justin, et al. “Soybean Gall Midge: An Emerging Pest of Soybeans.” CropWatch, 26 Nov. 2019, cropwatch.unl.edu/2019/soybean-gall-midge-emerging-pest-soybeans. Accessed 20 Oct. 2024.
4. “Soybean Tentiform Leafminer in Minnesota Soybean.” Extension at the University of Minnesota, 2023, extension.umn.edu/soybean-pest-management/soybean-tentiform-leafminer-minnesota-soybean. Accessed 20 Oct. 2024.
5. “Soybean Tentiform Leafminer in Minnesota Soybean.”