Nematodes are the most numerous (and least understood) multicellular animals on the planet, with over 20,000 species in the phylum Nemata. Nematodes can be free-living or can be parasites of insects, fungi, animals, and plants. Plant parasitic nematodes are microscopic soilborne worms that feed on nearly every plant species known and are found in nearly all environments that are hospitable to plant life.
While traditionally thought of as a pest of soybean, because of the prevalence of soybean cyst nematode, nematodes pose a growing threat to corn production. One or more nematode species can be found in Midwestern corn fields:
- Root Knot
Corn plant-parasitic nematodes feed on corn in different ways. The majority use a stylet to puncture the root cells to feed and spend their life-cycle either feeding on roots from the outside (ectoparasites) or from the inside of corn roots (endoparasites). Nematode species live in different soil environments; needle and sting prefer sandier soil environments and are frequent pests of corn grown in sandy soils. Often, nematode populations are concentrated in areas called “hot spots”, which may be randomly distributed across a field.
Symptoms of nematode feeding in corn are often not easy to distinguish, as they may mimic the symptoms of environmental stress, nutrient deficiency, or herbicide injury. The most common symptom is chlorosis (yellowing), other symptoms include an uneven stand, stunting, wilting, root necrosis, and root malformation. While these symptoms may be distinct, they are not unique to corn nematodes.
The most accurate way to assess corn nematode damage is by collecting and analyzing soil and root tissue samples. A generally accepted procedure for nematode sampling includes:
- Collecting nematode samples during the middle of the growing season.
- Collecting at least 20 soil cores from 12 inches deep near the corn roots,
- Collect samples from plants exhibiting symptoms and from healthy plants.
- Sampling the root systems of 3 to 5 corn plants, as nematodes may be residing inside the root system.
- Record background information such as field history, soil type, recent rainfall, and location of samples (hill, bottom ground, etc.)
- Submit samples to appropriate testing laboratory.1
There are no in-season remedies for nematode infestations; however, there are two management options available for the next growing season - crop rotation and nematicides. If growing a non-host crop is not a viable option, then using a nematicide can help minimize future damage. A nematicide corn seed treatment kills nematodes near the root zone, helps prevent feeding, and reduces the potential for disease transmission during the growing season. Nematicides have no residual benefit season-to-season and needs to be reapplied with planting each spring.
1Tylka, G. 2007. Nematodes in corn production: A growing problem? Integrated Crop Management. IC-498. Iowa State University Extension and Outreach. Iowa State University. https://crops.extension.iastate.edu/.
Jackson-Ziems, T. 2015. Sampling for nematodes of corn. Corn Nematode Sampling. CROPWATCH. University of Nebraska-Lincoln. https://cropwatch.unl.edu/.
Jackson, T. Nematodes. CROPWATCH. University of Nebraska-Lincoln. https://cropwatch.unl.edu/.
Web sites verified 5/19/2020
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