Start Scouting for Stalk Borers in Southern Iowa

June 10, 2022
ICM News

Stalk borer is an occasional pest of corn, but it can be persistent in some fields, especially those fields near fence rows, terraces, and waterways that serve as overwintering sites. Tracking degree days is a useful way to estimate when common stalk borer larvae begin moving into cornfields from their overwintering hosts. Foliar insecticide applications are only effective when larvae are migrating and exposed to the insecticide. Start scouting corn for larvae when 1,300-1,400 degree days (base 41°F) have accumulated. Parts of southern Iowa have reached this important benchmark (Figure 1); therefore, scouting for migrating larvae should begin now to make timely treatment decisions.

Growing degree days map.
Figure 1. Degree days accumulated (base 41°F) for stalk borer in Iowa (January 1 – June 6, 2022). Map courtesy of Iowa Environmental Mesonet, Iowa State University Department of Agronomy.

This encyclopedia article details stalk borer identification, sampling, and management and provides information on high-risk fields. Stalk borers tend to re-infest the same fields, so prioritize scouting fields with a history of stalk borers, paying close attention to field edges. Finding “dead heads” in nearby grasses or weeds is an indicator of stalk borers in the area. The larvae are not highly mobile and typically only move into the first four to six rows of corn. Young corn is particularly vulnerable to severe injury; plants are unlikely to be killed once they reach V7 (Photo 1).

Stalk borer larvae.
Photo 1. Stalk borer larvae can shred corn leaves and destroy the growing point.

No rescue treatments are available for stalk borer, but tracking degree days and scouting the field can determine whether larvae are present and still migrating. Insecticide applications are only effective while larvae are migrating to corn; once larvae have bored into the stalk, an insecticide will not reach them. Economic thresholds are based on market value and plant growth stage and may be found in the stalk borer encyclopedia article.

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 10, 2022. The information contained within may not be the most current and accurate depending on when it is accessed.

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Authors: 

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...