Seedcorn Maggots Emerging in Southern Iowa

April 13, 2022
ICM News

Seedcorn maggot larvae feed on germinating seeds or seedlings of corn and soybean (Photo 1). Feeding can delay development or kill the plant, and plant injury is especially prevalent during cool, wet springs when plants grow slowly. So far, this spring has been cooler and wetter than the past few years and this trend is expected to continue during the next couple of weeks. Despite planting progress being slow because of the weather, seedcorn maggot development has been on-track with previous years due to the few warm days we have had.

Seedcorn maggot on soybean. Photo by University of Minnesota Extension.
Photo 1. Seedcorn maggot on soybean. Photo by University of Minnesota Extension.  

Seedcorn maggot has a lower developmental threshold of 39°F and an upper threshold of 84°F. Peak adult emergence for the first generation occurs at 360 accumulated degree days (GDD) since January 1. Based on current GDD, the first generation of adult seedcorn maggot has likely emerged throughout most of western and southern Iowa (Figure 1).

Figure 1. Accumulated growing degree days (base 39°F) in Iowa from January 1 to April 11, 2022. Map courtesy of the Iowa Environmental Mesonet, Iowa State University Department of Agronomy.
Figure 1. Accumulated growing degree days (base 39°F) in Iowa from January 1 to April 11, 2022. Map courtesy of the Iowa Environmental Mesonet, Iowa State University Department of Agronomy.

It is recommended to avoid planting during peak adult emergence, because first-generation larvae typically emerge within a few days (414 GDD) and feed for several weeks (781 GDD). Remember that forecasted cooler temperatures would delay development of both seeds and insects, potentially increasing risk to seeds planted in mid-April. If possible, target planting during the “fly-free” period in areas at higher risk for seedcorn maggot. While no rescue treatments are available, cultural and chemical methods prior to or at planting can minimize risks. Read more about seedcorn maggot biology, risk factors, and management in this encyclopedia article. To confirm seedcorn maggot injury, check areas with stand loss and look for maggots, pupae, and damaged seeds (hollowed out seeds or poorly developing seedlings).

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on April 13, 2022. The information contained within may not be the most current and accurate depending on when it is accessed.

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Ashley Dean Education Extension Specialist I

Ashley is an education extension specialist for field crop entomology at Iowa State University. She coordinates the Iowa Moth Trapping Network, develops educational resources for field crop pests in Iowa, and aids in the research efforts of the

Erin Hodgson Professor

Dr. Erin Hodgson started working in the Department of Entomology at Iowa State University in 2009. She is a professor with extension and research responsibilities in corn and soybeans. She has a general background in integrated pest management (IPM) for field crops. Dr. Hodgson's current extensio...