There are more than 10 different types of nematodes that feed on corn in Iowa. They vary tremendously in size, biology and ability to cause damage. Determining if nematodes are damaging corn requires proper sample collection and interpretation of results. Below are some guidelines for checking fields.
Samples should be collected only from near symptomatic plants in fields. Corn plants damaged by nematode feeding will be stunted and/or have yellow foliage. Also, roots often will be stunted, swollen, lacking fine roots or have areas of brown or black dead tissue.
How to sample depends on corn growth stage.
- V6 corn growth stage or earlier: Collect a soil and root sample.
- V6 through R3 growth stage: Collect soil samples as described above, but root samples are not needed.
- After growth stage R4: Sampling is not recommended.
Nematode population densities are not consistently related to potential yield loss once plants reach the R4 stage. Therefore, sampling is not useful for assessing whether damage is occurring.
The number of nematodes necessary to damage corn varies widely among the nematode species. The likelihood of yield loss can be gauged only by determining the types and numbers of nematodes present in a field.
During the growing season, nothing can be done to reduce damage to corn caused by plant-parasitic nematodes.
Continuous cropping of corn seems to promote increases in the numbers of these harmful parasites and rotating corn with soybeans annually may help prevent nematode numbers from increasing to damaging levels.
Counter 20G is a soil-applied insecticide/nematicide that can be applied before planting if recurring damage from nematodes occurs in a field. Finally, several seed treatments are available to protect against nematodes that feed on corn.
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