Research HighlightsSoybean Pests in North Dakota Can Be Elusive: Be Prepared (Part 2 of 2)
Soybean Gall Midge May Be in North Dakota
By Carol Brown
The soybean gall midge was first documented in Nebraska in 2011 and described as a new species in 2018. This pest has since been found in Missouri, Iowa, Minnesota, and South Dakota. North Dakota State University Professor and Extension Entomologist Janet Knodel has been checking for its presence in the state for several years and has come up empty so far. But the soybean gall midge might have finally reached North Dakota.
“My postdoctoral scientist Veronica Calles-Torrez, the IPM crop scouts, and I started surveying North Dakota soybean fields for soybean gall midge infestations in 2019, and people kept saying that we must have it,” she says. “Through the IPM Crop Survey since 2020, we have kept increasing the number of fields scouted.”
Knodel is part of a multi-state project to survey for this pest, funded by the North Central Soybean Research Program and the North Dakota Soybean Council. She also leads the NDSU Extension IPM Crop Survey and is part of another NCSRP project exploring insecticide resistance in soybean aphids, the focus of Part 1 in this series.
North Dakota was in a drought during 2020 and 2021, which doesn’t favor the biology of most gall midges. They prefer moist soils for survival, so Knodel and her team weren’t surprised when they didn’t see midges in those years. However, 2022 may prove to be different as drought conditions have ended in most of the state.
“In mid-August, Brandon Schulzetenberg, a Centrol crop consultant, alerted us to a possible soybean gall midge infestation in a soybean field near Gwinner in Sargent County,” says Knodel. “After looking at the pictures he sent of larvae in the stem lesion (Figure 1), and the lack of white mold infection in the field, we quickly visited the site.”
After more than eight hours of scouting, they finally found at a field’s edge one stem with a lesion that had about 10 tiny, white to orange-reddish larvae. The lesion was located mid-plant, which suggests this was the second generation of soybean gall midge. Knodel noted that the infestation was obviously very low due to the difficulties in finding one midge-infested stem.
The team collected the larvae and sent them to Justin McMechan’s entomology laboratory at the University of Nebraska to determine with DNA testing whether they are a match for soybean gall midge or white mold gall midge. The DNA test results indicated a 89-92% match for soybean gall midge, which is too low for a 100% positive identification. However, the DNA test for white mold gall midge was 100% negative, and white mold was not present in the field where the larvae were found, allowing them to rule out this species.
“We believe this will be the first positive identification for soybean gall midge in North Dakota, however we will need to continue surveying and collecting more larvae in 2023 to confirm its presence,” says Knodel. “NDSU Extension Entomology has been quite proactive in surveying for soybean gall midge due to support from the North Dakota Soybean Council and the NCSRP.”
White Mold Gall Midge Resemblance
“There are complications with scouting for the soybean gall midge, as it is easily mistaken for a beneficial look-a-like,” Knodel says. “Present in North Dakota, the white mold gall midge feeds on Sclerotinia sclerotiorum, the fungus that causes white mold in soybeans, and these two midges, especially the larval stage, can be easily confused.”
Both midges have white to orange-colored larvae, and adult midges are small and similar in appearance. Knodel says the white mold gall midge is found in North Dakota and other states on crops such as dry beans and sunflower, which also can be infected with white mold. To help identify the white mold gall midge, she authored a fact sheet that shows comparisons between the two midge species.
Because of the similarity between the two midge species, any larvae or midge suspect of being a soybean gall midge that Knodel and the IPM crop scouts find is sent to McMechan’s lab for positive identification. They have been exceptionally thorough in their scouting for this new pest. The team surveyed a total of 78 fields in 11 counties in 2019, 605 fields in 47 counties in 2020, and 588 fields in 48 counties in 2021. In 2022, they surveyed 435 soybean fields in 45 counties for soybean gall midge, all of which were negative — except for one field in Sargent County.
The possible positive identification of soybean gall midge in North Dakota is not the best news farmers could receive. But Knodel and the IPM crop scouts will have even more heightened awareness now if the results are positive for the new pest. With drought conditions ending in most of the state, she and her team will keep a diligent watch and offer help for farmers with managing this pest.
SRIN information page: https://soybeanresearchinfo.com/soybean-pest/soybean-gall-midge/
Published: Feb 13, 2023
The materials on SRIN were funded with checkoff dollars from United Soybean Board and the North Central Soybean Research Program. To find checkoff funded research related to this research highlight or to see other checkoff research projects, please visit the National Soybean Checkoff Research Database.