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5/21/2012 - 5/27/2012

Crop Minute - Time to Scout Corn

It is time for producers to scout corn fields and identify corn establishment problems such as damping off and rootworm egg hatch, according to extension specialists. In her Crop Minute, Erin Hodgson, extension entomologist, says rootworms have hatched early. Alison Robertson, extension crop pathologist, notes in her Crop Minute some corn plants are experiencing problems in southeast Iowa, but it's not all due to disease.

Crop Scouting Cards Now Available

By Daren Mueller, Department of Plant Pathology and Microbiology

Farmers and crop scouts can identify and keep track of soybean and corn field problems throughout the season by using a new series of field crop scouting cards. The cards were produced by the Iowa State University (ISU) Integrated Pest Management program with support from the Iowa Soybean Association (ISA).  

The series includes nine scouting cards: early, mid- and late-season soybean scouting; early, mid- and late-season corn scouting; and problem-specific cards for white mold, soybean aphid and stink bugs. The cards can be used as a recordkeeping tool to track pest problems in specific fields over time, which then can be referenced when making future decisions. Color images and descriptions on disease and pest cards simplify the identification of crop issues.

Identifying insects, diseases and other issues is a critical part of making good management decisions in corn and soybean. These publications can be used by crop scouts as a calling card to let the farmer know the field has been scouted and as a record of any problems in the field.

The scouting cards were developed to complement ISU's field guide series. Several publications in the field guide series and the soybean scouting cards were partially funded by ISA through the soybean checkoff. For more than 40 years, the soybean checkoff program has been working with leading researchers and extension specialists at ISU to provide Iowa’s farmers the latest agronomic information. These guides are another in a series of joint publications all aimed at helping soybean farmers more effectively manage their soybean acres.

Scouting cards can be ordered from the ISU Extension and Outreach Online Store or by calling (515) 294-5247 and requesting the appropriate publication. Copies of the soybean scouting cards can also be obtained by contacting ISA at 800-383-1423; pdfs are also available.


Daren Mueller is an extension specialist with responsibilities in the Iowa State University Integrated Pest Management program. Contact him at 515-460-8000 or e-mail

Predicted Corn Rootworm Hatch Begins for 2012

By Erin Hodgson, Department of Entomology and Adam Sisson, Integrated Pest Management

Corn rootworm egg hatch in Iowa can occur from late May to the middle of June, depending on accumulating soil degree days, but the average hatching date is around June 6th. Research suggests about 50 percent of egg hatch occurs between 684-767 degree days (base 52°F, soil). Although Iowa had a warmer than normal March, soil temperatures have been closer to normal in April and May. So the 2012 predicted corn rootworm egg hatch is only slightly ahead of normal (Photo 1), but about two weeks ahead of the 2011 growing season. The southwest region in Iowa is experiencing 50 percent egg hatch now and other parts of the state will approach it within 7-14 days depending on the temperature. Other states have also reported that corn rootworm egg hatch is underway. Illinois is reporting the earliest initial egg hatch in 35 years.

Predicted corn rootworm egg hatch in Iowa for 2012. Expect 50 percent hatch to between 684-767 degree days. Map data courtesy of Iowa Environmental Mesonet, ISU Department of Agronomy - home of
 current degree day accumulation for corn rootworm.


Roger Elmore, ISU Corn Extension Agronomist, recently reported Iowa is 6 percent ahead of a normal corn planting year. So although predicted corn rootworm egg hatch is slightly ahead of normal, the larvae should have sufficient root tissue to feed on because most corn will be germinated by the time the eggs hatch. Saturated soils will diminish overall corn rootworm pressure, and the high adoption of Bt corn should decrease populations in most fields. However, I anticipate a good larval establishment this year. Early egg hatch could mean we see earlier adult corn rootworm emergence, too.

Shortly after egg hatch, young larvae will begin feeding on root hairs and inside roots. As they develop, larvae will begin feeding on root tips. A severe infestation can destroy nodes 4-6 which interferes with water/nutrient uptake and makes the plant unstable. Every field should be scouted for corn rootworm damage regardless of the seed selection (i.e., dig and rate corn roots even if Bt proteins are used). Continuous corn fields and areas with persistent corn rootworm populations are the highest priority for inspection. Assess corn rootworm root injury and adjust management strategies if the average injury is above 0.5 on a 0-3 rating scale (Photo 2). Aaron Gassmann (ISU Corn Entomologist) has a webpage for additional corn rootworm management information, including an interactive node-injury scale demonstration and efficacy evaluations.

Rating corn rootworm damage is essential for assessing current management plans. Photo by Brent Pringnitz.

Erin Hodgson is an assistant professor of entomology with extension and research responsibilities; contact at or phone 515-294-2847. Adam Sisson is an Integrated Pest Management program assistant. Sisson can be contacted by email at or by calling 515-294-5899.

This article was published originally on 5/28/2012 The information contained within the article may or may not be up to date depending on when you are accessing the information.

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