All plants can act as hosts of plant-parasitic nematodes and field corn is no exception. Plant-parasitic nematodes attack and feed on the roots of plants disrupting the plant’s ability to take up water and nutrients.
The most common above-ground symptoms include yellowing, wilting, and stunting of corn plants. Field symptoms are more noticeable early in the season and appear as spots or patches in the field. Below-ground symptoms appear as lesions on roots, swollen areas or galls, lack of fine roots and a general stubby appearance to the root system.
Nematodes can cause damage and loss of yield without apparent above ground symptoms making it difficult to recognize the disorder in the field.
Nematode population density, soil type, and environmental conditions all play a factor is the level of yield loss. Sandier soils and fields dealing with other problems such as compaction or fertility deficiencies are more likely to suffer damage from nematodes.
The most common nematodes effecting corn include the southern root-knot, lance, lesion, stubby-root, and stunt. Root-knot nematodes produce small galls on the roots a few weeks into the season. Southern root-knot nematode can also attack common rotational crops including cotton and soybean.
Collecting soil samples are the most reliable method to correctly determine what nematodes are present in the field. Soil samples should be collected during the growing season through harvest. Soil samples should be collected to a depth of 6 to 8 inches from 15-20 sites in the area that you suspect nematode problems. The soil should not be excessively wet or dry at the time collected, and once collected should be kept cool until they can be sent to the Plant Diagnostic Laboratory for analysis.
Management typically begins with crop rotation for most problematic nematodes with southern root-knot the one exception because of its wide host range. Peanuts are not a host of southern root-knot nematodes and could be a considered a rotational partner in Alabama.
All corn varieties are considered susceptible to southern root-knot, but some cotton and soybean varieties have resistance to this species and can be rotated with corn to reduce nematode populations. Other management practices to reduce damage from plant-parasitic nematodes include following a proper fertility program, reducing soil hard pans in problematic fields and avoiding water stress through irrigation when practical.
There are a few nematicides that can be used to protect against nematodes. Please refer to the Alabama Corn IPM Guide for more information.
Dr. Ed Sekora is an Auburn University Extension plant pathologist. He may be reached at Ed Sekora.