Corn Rootworm egg Hatch Behind Schedule this Year

June 21, 2022
ICM News

Corn rootworm egg hatch in Iowa typically occurs from late May to the middle of June, with an average peak hatching date of June 6 in central Iowa. Even with recent warm temperatures, hatching is a bit delayed this year due to cool spring temperatures. Development is driven by soil temperature and measured by growing degree days (GDDs). Research suggests about 50% of egg hatch occurs between 684-767 accumulated GDDs (since January 1; base 52°F, soil). Many areas have reached peak corn rootworm egg hatch, and the northern portion of the state could experience peak hatch within a week (Figure 1).

Accumulated soil degree days in Iowa.
Figure 1. Accumulated soil degree days (base 52°F) in Iowa as of June 20, 2022. Expect 50% egg hatch of corn rootworm between 684-767 degree days. (Map courtesy of Iowa Environmental Mesonet, Iowa State University Department of Agronomy.)

To predict corn rootworm egg hatch for your area based on degree day accumulation, use the Iowa State Agronomy Environmental Mesonet websiteSet the start date to January 1 of the current year, use the current date for the end date, and make sure the plot parameter is set to “soil growing degree days (base = 52).”

A severe corn rootworm larval infestation can destroy nodes 4-6; each node has approximately 10 nodal roots. Root pruning interferes with water and nutrient uptake and makes the plant unstable (Figure 2). Recent research predicts a 15% yield loss for every node pruned back to 1 ½ inches. Prolonged drought can exacerbate root injury and cause additional yield loss.

Severe root pruning by corn rootworm larvae.
Figure 2. Severe root pruning by corn rootworm larvae can dramatically impact yield. (Photo by Erin Hodgson, Iowa State University.)

Regardless of agronomic practices used to suppress corn rootworm (e.g., crop rotation, Bt hybrids, or soil-applied insecticides), every corn field should be scouted for corn rootworm root injury. Continuous corn fields and areas with Bt trait performance issues are the highest priority for inspection. It is ideal to look at corn roots 10-14 days after peak egg hatch because the feeding injury will be fresh. On some hybrids, corn roots can grow back and make it difficult to assess feeding injury later in the season. Assess corn rootworm feeding and adjust management strategies if the average injury is above 0.5 on the ISU 0 to 3 Node Injury Scale. Also consider monitoring for adult corn rootworm to supplement root injury assessments.

To refresh your root injury assessment skills, consider attending one of the seven corn rootworm demonstrations occurring in Iowa this summer.

Additional resources:

Aaron Gassmann’s webpage:

Corn rootworm IPM:

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 June 21, 2022. The information contained within may not be the most current and accurate depending on when it is accessed.


Ashley Dean Agriculture and Natural Resources Extension Specialist II

Ashley is an education extension specialist for field crop entomology at Iowa State University. She coordinates the Iowa Moth Trapping Network, the Regional Corn Rootworm Monitoring Network, and the Iowa Pest Alert Network. She also develops educational resources for field crop pests in Iowa and ...

Erin Hodgson Professor

Dr. Erin Hodgson started working in the Department of Entomology, now the Department of Plant Pathology, Entomology, and Microbiology, 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...