Are nematodes damaging corn?

There is considerable interest and continued discussion among growers, agronomists and university researchers about plant-parasitic nematodes that feed on corn.

Are nematodes damaging corn?


There is considerable interest and continued discussion among growers, agronomists and university researchers about plant-parasitic nematodes that feed on corn.

To find out if these microscopic worms are damaging a corn crop, soil and roots must be collected and sent to a qualified laboratory to determine which specific nematodes are present and at what population densities (number of nematodes in the soil).

Key Points

• Many wonder if nematodes are doing damage on corn roots.

• Are nematodes causing crop injury symptoms in your fields?

• Collect soil and root samples and have them tested.


“Samples should be collected only from fields that are showing obvious symptoms of possible nematode damage, such as yellow leaves, stunting or midday wilting. That’s because there is no evidence presently to indicate that nematodes can damage corn plants and reduce corn yields without obvious symptoms of that damage appearing during the growing season,” says Greg Tylka, an Iowa State University Extension plant pathologist and nematode expert.

Collect samples correctly

Following are some guidelines offered by Tylka on how to collect a soil sample for corn nematode testing.

“You want to determine if the visible symptoms you are observing in a field are being caused by plant-parasitic nematodes feeding on the corn roots,” he notes.

• Collect 15 to 20 12-inch-deep soil cores from the root zone of plants with symptoms.

• Collect four root masses; stalks can be cut off and discarded, as well as soil adhering to roots.

• Place soil cores in a sealed plastic bag; roots can be placed in a separate plastic bag.

• Protect the samples from temperatures above 80 degrees F, and handle them with care.

• Deliver or send the samples to a lab for processing as quickly as possible. Avoid sending samples on Thursdays and Fridays so they don’t sit in delivery trucks over the weekend.

These guidelines are for all situations except when nematode damage is suspected on soils with at least 70% sand, says Tylka. Sandy soils may be infested with the needle nematode or the sting nematode, and both types are difficult to find in samples collected in the middle of the growing season. Spring and fall sampling are recommended for these nematodes. 

Additional details about sampling sandy soils for plant-parasitic nematodes that can feed on corn are available in the May 18 issue of ISU’s Integrated Crop Management newsletter, which you can access for free on the ISU website.

Several private laboratories and most land-grant university plant diagnostic labs can process soil samples and determine the identities and numbers of plant-parasitic nematodes present. The address of the ISU facility is: Plant and Insect Diagnostic Clinic, Room 327 Bessey Hall, Iowa State University, Ames, IA 50011.

The test for corn nematodes from the ISU Plant and Insect Diagnostic Clinic is called the “complete nematode count.” Samples should be accompanied by a completed Plant Nematode Sample Submission Form, PD 32, and a check for the $30-per-sample processing fee ($60 per sample if the sample is from outside of Iowa).

For more information about corn nematodes, see the ISU Extension publication titled “Nematodes that Attack Corn in Iowa.” Swollen roots, stunted plants and barren ears are other possible nematode symptoms.

Source: ISU Extension

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CHECK SOIL: For corn nematode sampling, collect 20 or so 12-inch-deep soil cores from the root zone of plants showing possible symptoms of nematode damage.

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CHECK ROOTS: Collect four root masses; stalks can be cut off and discarded, and soil can be carefully shaken from roots and discarded.

This article published in the August, 2010 edition of WALLACES FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.

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