Curious Cutworms in Soybean Fields

June 3, 2010
ICM News

Erin Hodgson, Department of Entomology

In the last two weeks, I've heard reports of cutworm damage in soybean. Rich Pope visited a commercial soybean field in Harrison County and identified a mixture of black cutworm and dingy cutworm (Fig. 1). Matt O'Neal, ISU soybean entomologist, confirmed cutworm damage in soybean research plots at Curtiss Farm just south of Ames in Story County. The small cage plots were also infested with a combination of cutworm species (Fig. 2). It can be difficult to distinguish cutworm species without a hand lens, but a previous ICM article can help with identification


Fig 1. A field in Harrison County, Iowa showing 50-60 percent stand loss due to cutworms. Photo by Rich Pope.


Fig 2. Cutworms found in Story County, Iowa.

Cutworm damage in corn is reported almost every year in Iowa. But infestations are patchy and sporadic because they have to migrate here every spring. On the other hand, cutworm damage in soybean is not typical. The last time cutworm damage was reported in ICM News was in 1999 by Marlin Rice. Entomologists don't fully understand why cutworms sometimes cause damage to soybean. However, there are a few field conditions that may make soybean fields attractive to female cutworm moths:

• Fields planted under reduced or no-tillage practices

• Fair to poorly drained fields

• Fields with winter annual weeds emerged prior to soybean planting

• More likely found in fields previously infested with cutworms

Economic thresholds have not been developed because infestations are unpredictable and infrequent. Treatment decisions must be based on the size of the cutworms and level of infestation. In some cases of very heavy cutworm density, fields may have to be replanted. Check 20 consecutive plants in five different areas of the field to determine percent cutworm damage. Young cutworms may feed on the stem or leaves, but older larvae can clip off the cotyledons. Also, look for discolored, wilted or dead plants. Cutworms will seek shelter during the day, so dig 2-3 inches down in the soil within a row. Consider an insecticide if larvae are less than 3/4 inch long and more than 20 percent of plants are damaged or missing.


Erin Hodgson is an assistant professor of entomology with extension and research responsibilities. She can be contacted by email at or phone (515) 294-2847.

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 3, 2010. The information contained within may not be the most current and accurate depending on when it is accessed.


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...