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2/27/2012 - 3/4/2012

Spring Sampling Not Recommended for Nematodes on Corn – Except for Sandy Fields

By Greg Tylka, Department of Plant Pathology and Microbiology

Most Iowa cornfields harbor one or more species of these microscopic, plant-parasitic worms. At least 28 nematode species have been found associated with corn in Iowa. Most are not thought to cause damage at low population densities (numbers). The estimated damage threshold for most nematodes that feed on corn in Iowa ranges from 100 to 1,000 worms per half-cup (100 cc) of soil (see August 2009 ICM News article). Only dagger, needle and sting nematodes are considered damaging at low numbers.  The results of Iowa State University testing, from 2000 to 2010, for nematodes that feed on corn in the state were summarized in a recent ICM News article.

Sample timing is key
Knowing the types and numbers of nematodes present in a field is useful in gauging the possible benefits of nematode-protectant seed treatments or soil-applied nematicides. Unfortunately, most nematode numbers will be low in spring soil samples, even though they can develop to higher, damaging levels later in the season. Because of this, results of spring soil samples usually are not useful and collecting such samples in the spring is not recommended.

The only situation in which spring sampling for nematodes that feed on corn is warranted is in fields where the soil has at least 70 percent sand. These fields may be infested with the needle (figures 1 and 2) and sting nematodes, which are damaging at very low numbers. The needle and sting nematodes migrate to deeper depths in the soil in the middle of the growing season and can be missed in mid-season soil samples that would be collected for the other nematode species. Consequently, spring soil sampling is recommended for these two nematode species in sandy fields.

Collect and store the samples properly
Spring sampling of sandy soils for nematodes is simple:

  • Use a soil probe and collect cores that are at least 12 inches long.
  • Collect 20 or more soil cores to represent an area.
  • Sample from areas of the field where corn has not grown well in previous years.
  • Combine, but do not mix, the soil cores and store them in a sealed plastic bag that is labeled with permanent marker.
  • Protect the samples from physical jarring and from high temperatures (above room temperature).
  • Send a completed Plant Nematode Sample Submission Form along with the soil samples to the Iowa State University Plant and Insect Diagnostic Clinic at the address below, requesting a complete nematode analysis.

Plant and Insect Diagnostic Clinic
327 Bessey Hall
Department of Plant Pathology and Microbiology
Iowa State University
Ames, IA 50011-1020

The current fee for a complete nematode analysis (the test for nematodes that feed on corn) at the ISU clinic is $30 per sample for samples from Iowa. Call the ISU clinic at 515-294-0581 to check about processing of soil samples from outside Iowa. A list of other land-grant university facilities that process samples for nematodes that feed on corn is available online.

More information about nematodes that feed on corn
There have been numerous articles in ICM News in the past several years that discuss aspects of the biology, sampling and management of nematodes that feed on corn. To find these articles, search for “nematodes on corn” in the search box in the upper left corner of the ICM News home page.

Also, there is an ISU Extension bulletin titled Nematodes That Attack Corn in Iowa (PM 1027), that was written by Don Norton, former ISU research nematologist and expert on nematodes that feed on corn.

Figure 1. Corn roots damaged by needle nematode feeding.


Figure 2. Needle nematodes with damaged roots and sewing needle. Photo credit Purdue University IPM Program – watch video


Greg Tylka is a professor with extension and research responsibilities in management of plant-parasitic nematode in the Department of Plant Pathology and Microbiology at Iowa State University. He can be reached at or 515-294-3021.

Cooperators Needed for Black Cutworm Monitoring

By Adam Sisson, Integrated Pest Management

Cutworm monitoring time is nearing – and the Integrated Pest Management (IPM) program at Iowa State University is now recruiting cooperators for 2012. The ISU Plant and Insect Diagnostic Clinic and IPM program are coordinating the annual black cutworm (BCW) monitoring network in Iowa. Farmers and agribusiness personnel are needed to monitor BCW traps for the arrival of cutworm moths this spring.

Black cutworm monitoring will begin April 1. Cooperators will be sent a cutworm trap to assemble and place; they then are asked to monitor the trap every other day. Cooperators record the number of moths and enter the data at at least once per week. Trap monitoring stops near the beginning of June. Trap data, along with degree days, is used to estimate when farmers should be scouting. Scouting will determine if treatment for BCW is necessary in a field.

Black Cutworm moth pheromone trap.

To become a cooperator, e-mail with your name, address and county where trap will be placed. Cooperators will receive a trap kit in the mail with supplies, instructions and pest identification information. The target sign-up deadline is mid-March to allow enough time for shipping. More information about BCW in Iowa can be found in a May 2011 ICM News article.


Black cutworm moth.


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 3/5/2012 The information contained within the article may or may not be up to date depending on when you are accessing the information.

Links to this material are strongly encouraged. This article may be republished without further permission if it is published as written and includes credit to the author, Integrated Crop Management News and Iowa State University Extension. Prior permission from the author is required if this article is republished in any other manner.