Plant-parasitic nematodes can seriously injure corn, and there are numerous species known to affect corn in Iowa. The Iowa State University (ISU) Plant Disease Clinic has received several samples in the past few weeks from fields with corn damaged by the needle nematode. Plants from these fields were stunted and yellow and many of the roots were swollen.
The needle nematode is restricted to sandy soils because of its large size. It is one of the most damaging nematodes to corn. It can cause injury at any population density, so if this nematode is detected in a sample, damage is likely.
|Young corn crop damaged by needle nematode. Photo courtesy of Tom Hillyer.|
|Swollen, stunted corn roots caused by needle nematode feeding.|
To determine whether needle nematode is responsible for causing stunted or yellow corn, a soil sample must be submitted. Although needle nematodes can move down into the soil profile in the heat of summer, our experiences in the Plant Disease Clinic over the past few years indicate that we can still detect this nematode in soil samples collected in July and August.
Collect a soil core or small shovel-full of soil from the upper foot of the soil profile from the root zone of 10 or more plants within the area suspected of being damaged by the nematodes. Soil should be placed in a moisture-proof bag and submitted for processing as soon as possible. Be sure to keep the samples cool until they are sent for processing and avoid sending samples late in the week to prevent improper storage over the weekend.
Soil samples for analysis of corn nematodes can be sent to several private laboratories in Iowa and surrounding states or sent to the Iowa State University Plant Disease Clinic, 323 Bessey Hall, Iowa State University, Ames, IA 50011. If samples are sent to ISU, the test for corn nematodes is called a complete nematode count. Samples should be accompanied by a completed Plant Nematode Sample Submission Form  (PDF) (ISU Extension publication PD 32) and a check for the $15 per sample processing fee ($20 per sample for out-of-state samples).
This article originally appeared on pages 157-158 of the IC-488(19) -- July 29, 2002 issue.