Late plantings in 2019 may have helped combat a pest problem that has popped up in recent years, according to an Iowa State University Extension researcher.
Erin Hodgson, an Extension entomologist, studies gall midge, an insect that primarily has affected soybeans.
“Our observations were late-planted fields were not as attractive as early-planted fields,” Hodgson said.
Soybean gall midge is still a relatively new issue for producers in the Midwest, with the first cases documented in Nebraska coming in 2011 and South Dakota in 2015. Now, the issue has spread largely into western Iowa, southwest Minnesota and northwest Missouri, said Pat Holloway, a field agronomist from Beck’s Hybrids.
Holloway said the pest is likely to continue to spread across soybean fields in the Midwest.
“With so little known currently about the pest, it will take time to determine effective control measures, but work being done by universities in the states affected will hopefully lead to best management practices in the near future,” he said.
Much of the damage from gall midge comes from their reproductive cycle. Eggs are laid by the base of the plant and larvae feed on the inside of the stem, causing structural issues. That may cause a plant to die within 7-10 days of infestation, Hodgson said, which could result in complete yield loss.
She said plant death is highest at the edge of fields, as overwintering females lay eggs there first. Some of the symptoms could be easily misidentified.
“Subsequent generations move to healthy plants in the field interior,” Hodgson said. “Midge infestations can be confused with fungal pathogens. Initial symptoms appear similar to soybean pathogens commonly seen in Iowa.”
Holloway is seeing the same thing, with the worst plant damage coming within 50-100 feet of the edge of the field.
Hodgson said 26 counties in Iowa have been confirmed with the insects, seven of which were new in 2019. She said it’s hard to predict how much it might spread this season.
Fields that have been impacted in the past are likely at risk this year, Holloway said, citing some of the gall midge limitations.
“The adults are weak flyers, and therefore they primarily impact the field edges adjacent to fields that were infected the prior year,” he said.
As for combating the issue, Hodgson said her labs were unable to find much that is helping at the moment.
“Unfortunately, we did not see any effective insecticides to suppress adults or larvae,” she said. “Part of the issue was application timing.”
She said with gall midge still being a relatively new issue, there is not enough information known about the biology and life cycle of the insect to properly time treatments yet. Her lab’s goal is to refine efficacy evaluation is 2020.