Check for Wireworm Injury When Assessing Corn Stands

May 28, 2015
ICM News

By Rebecca Ahlers, Department of Agronomy and Erin Hodgson, Department of Entomology


Last week, (May 19-22, 2015), some wireworm activity was noted in south-central Iowa. Ideally, scouting for wireworms should occur prior to planting because there are no effective rescue treatments. However, most people don’t see the impact this pest can have on a corn stand until corn plants emerge. While assessing corn stands for black cutworm and armyworm feeding, individuals should also consider assessing for wireworm activity.



Identification


Wireworms are slender larva and range from ½ to 1-1/2 inches (13 to 38 mm) in length. (Photo 1). There are soft- and hard-bodied wireworm species that are pale white or shiny yellow to brown in color. Wireworms have three pairs of legs near the head and lack any fleshy, abdominal prolegs. There is an obvious pair of appendages on the last abdominal segment that form a “keyhole.”



Photo 1: This hard-bodied wireworm was found in a field near Ottumwa, Iowa, on May 22, 2015. Photo by Rebecca Ahlers.


Biology


Wireworms are the larvae of click beetles. Female click beetles lay their eggs around the roots of grasses, which is why wireworms can be problematic in fields with a history of sod. Wireworms can also be found in land that has transitioned from CRP or pasture. It is unclear why wireworms are present in fields without a history of grasses. Wireworms can have an extended development and may live in the soil for up to 6 or 7 years where they feed on the roots of plants, particularly grasses.  


Plant Damage


Wireworm feeding commonly occurs when corn is planted early and the weather turns cold, slowing germination. They are more likely to be found in well-drained soils on ridgetops or hillsides. Wireworms feed on the germ of corn kernels, hollowing out seeds sometimes only leaving the seed coat. This will result in gaps in the rows. Wireworms will also feed on the underground portion of the root or stem of young corn plants by tunneling into them (Photo 2). Plants with this type of feeding usually appear stunted or wilted compared to surrounding plants. As soils warm up, wireworms will move deeper in the soil profile, posing less of a threat to corn seedlings. 



Photo 2: Wireworms can feed on corn seedlings and tunnel belowground. Photo taken on May 22, 2015 by Rebecca Ahlers.


Management


Fields with a history of wireworm injury should be sampled prior to planting. Unfortunately, there is no rescue treatment available for fields with significant stand loss from wireworms. Instead insecticidal treatment needs to occur before or at planting time. Treatments would include the use of a seed treatment or a soil-applied insecticide. If a field has significant stand loss, replanting is an option. Table 1 may help in making a replant decision. Consider the seed and insecticide costs associated with replanting as well as the extended weather forecasts and the hybrid maturity before making a replant decision.


Table 1. Relative yield potential of corn by planting date and population  



Rebecca Ahlers is an Extension Field Agronomist in Southeast/South Central Iowa. She can be reached at rka8@iastate.edu or by calling 319-643-811. Erin Hodgson is an associate professor of entomology with extension and research responsibilities; contact her at ewh@iastate.edu or by calling 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 May 28, 2015. The information contained within may not be the most current and accurate depending on when it is accessed.

Crop: 
Authors: 

Rebecca Vittetoe Field Agronomist in SC Iowa

Rebecca Vittetoe is an extension field agronomist in southeast/south central Iowa. Educational programs are available for farmers, agribusiness, pesticide applicators, and certified crop advisors.

Areas of expertise include agronomy, field crop production and management of corn, so...

Erin Hodgson Associate Professor

Dr. Erin Hodgson started working in the Department of Entomology at Iowa State University in 2009. She is an associate 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 curre...