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Nematodes can cause damage by feeding on corn roots which can reduce the plant’s ability to take up water and nutrients. Damage caused by root feeding can further injure a plant by allowing fungal and bacterial pathogens to enter the plant. Nematodes are also known to transmit viruses to the plants they feed on.
“Nematodes can make everything else worse,65533;? says Clemson University plant pathologist John Mueller. “A corn root system infected with nematodes can exhibit additional moisture stress, reduced nutrient uptake and lost yield potential. Without effective management, nematode numbers can increase year-to-year, reducing yield potential of the current corn crop as well as other crops in the rotation.65533;? (J.H. Hudson, personal communication, May 13, 2013)
Symptoms of nematode feeding are most noticeable when environmental conditions cause plant stress. Common above-ground symptoms include wilting, yellowing, and stunting of growth. However, nematodes may cause yield loss without exhibiting above-ground symptoms. Common below-ground symptoms include swollen roots, lack of fine roots, minimal root branching, and necrotic lesions. Below-ground symptoms can differ depending on which nematode is causing injury. For instance, different symptoms result from feeding by lesion, sting, or stubby root nematodes. In many cases nematode feeding occurs at the growth point of the root, and the resulting damage is apparent as stunted roots. Severe nematode damage will result in “stubby roots65533;? with many short, swollen roots.
Some of these agronomic practices include continuous corn, reduced tillage, and less use of soil-applied insecticides.
To confirm the presence of nematodes, soil and root samples must be taken and submitted to a nematode testing facility. Treatment recommendations can be made after test results confirm nematode species and approximate population density. Refer to university recommendations for treatment thresholds.
Nematode distribution can be very irregular within a field, therefore it is important to collect several composite samples to provide an accurate population estimate. When testing a field with no symptoms of nematode damage only a general field survey is needed to determine nematode species and population and help assess risk levels. Since nematode treatment thresholds vary by soil type, fields should be divided into zones by soil texture, and separate samples should be collected for each zone.
If nematodes are a current or suspected problem, samples should be collected around the edges of symptomatic areas, and some samples should include roots of the crop. Sampling should occur while the crop is growing and when soils are not overly wet or dry. Nematode numbers will be higher, and easier to detect, later in the growing season. Plant pathologists also caution that weeds can allow nematode numbers to increase even after crop harvest.
When collecting and shipping samples, handle with care to avoid killing nematodes before they reach the lab. Follow lab instructions for collecting, handling and shipping all nematode samples. A good sample will provide a reliable diagnosis and management strategy.
Because there are many nematode species, identification is essential for determining the appropriate control option. For certain nematode populations the best management practice is crop rotation. Corn management practices that reduce crop stress may help the crop overcome nematode attacks. The following agronomic practices may help growers manage potential nematode infestations.