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Nematodes are a common problem in corn, too

When farmers hear the word "nematode," they usually think of soybean cyst nematodes, but nematodes can also be the culprit of damage in corn.

Tamra Jackson, University of Nebraska Extension plant pathologist said, "Plant parasitic nematodes of corn are often overlooked as causes of disease and yield loss. Many farmers have to deal with damage caused by corn nematodes."


CORN NEMATODES--University of Nebraska Extension plant pathologist Tamra Jackson discussed corn nematodes during a recent field day. (Journal photo by Jennifer Bremer.)

She said some causes of the increase in this problem include the shift to continuous corn and the reduction in soil insecticide use, which is not affective against corn nematodes.

"Changes in insecticide chemistries has led us to expect more corn nematode damage," she said.

Corn nematode facts

Jackson said in contrast to soybean nematodes, there are many types of nematodes that can damage corn. Each of the nematodes can be present with or without the presence of others.

High-risk corn nematodes include sting and needle nematodes. Moderate-risk corn nematodes include stubby-root, lance and lesion nematodes. Low- or undetermined-risk nematodes include spiral, stunt and dagger nematodes.

Despite the myth, that corn nematodes are only present in sandy soil, Jackson said they can occur in every soil type.

"Corn nematode damage is very common and frequently misdiagnosed," she said.

Unlike soybean cyst nematode, which is a recently introduced pest, corn nematodes are probably native parasites that fed on prairie grasses before corn was cultivated. Every field has them, and their vivid names convey the trouble they can cause.

Symptoms

Nematodes injure corn plants by feeding on the roots and by creating wounds that allow bacteria, fungi and other pathogens to infect the plant and cause secondary rots. Damage is intensified by environmental stresses, such as seedling diseases, insect feeding and drought.

Symptoms include thin stands, uneven plant height, stunted plants, uneven tasseling, leaf yellowing, small ears and kernels and swollen, stunted or discolored roots. Unfortunately, these symptoms mimic other production problems, such as weather stress, nutrient deficiency, insect injury, herbicide damage or soil compaction, Jackson said.

Because of this, corn nematodes can't be diagnosed from symptoms alone, and must be confirmed by soil and root analysis. But, if you have an unexplained problem in corn, the culprit could be nematodes.

"Nematodes may be distributed over an entire field, but the most concentrated population densities are in patches that are seemingly randomly distributed in the field. This distribution can cause the development of 'hot spots' in a field," said Jackson. "In the most severe cases, plants at the center of these hot spots can die due to the severe injury or at least sustain substantial root injury."

Sampling

Because disease caused by nematodes cannot be diagnosed based only on plant symptoms, it is necessary to collect samples and submit them to a laboratory for analysis.

Samples should be taken both at the problem spot and at another location near to the problem spot.

Jackson said it is important to estimate the population densities of nematodes both in the soil and inside the root tissue when conducting a nematode analysis.

Some labs may require collection of separate root samples in addition to soil samples when conducting nematode analysis. She suggested contacting the local laboratory, to confirm that they conduct nematode analyses and for specific instructions on sample submission and associated fees.

"Nematode management in corn can be difficult because of the chronic nature of the problem," said Jackson.

Crop rotation may or may not be effective as determined by the feeding tendencies of the nematode species in the field. Some soil-applied nematicides are labeled for use on corn but, until recently, the narrow profit margin of the crop has limited their use except under severe nematode pressure.

For more information, visit the University of Nebraska plant disease website at www.pdc.unl.edu.

Jennifer Bremer can be reached by phone at 515-833-2120 or by e-mail at jbremer@hpj.com.



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