CORN NEMATODES IN MINNESOTA?
By Dave Pfarr
The soybean cyst nematode takes top honors for prevalence across Minnesota and its ability to cause widespread economic damage.
Of less importance to most producers is the feeding damage caused by nematodes on corn.
However, nematodes acting as root parasites on corn can be prevalent and cause significant yield loss in coarse textured or "sandy" soils in Minnesota.
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Recent production practices such as continuous corn cropping systems, reduced tillage, and reduced use of carbamate and organophosphate insecticides have led to more farmers noticing the yield-robbing effects of corn nematode feeding.
Numerous species of parasitic nematodes attack corn roots in the Corn Belt of the United States.
In general, these parasitic worms are aquatic and need free moisture to move to a feeding site on corn roots. Their aquatic nature also determines where they may be found during the growing season.
During spring and early summer, soil moisture levels near the soil surface will support the survival and mobility of corn nematodes as they feed on the root systems of developing corn plants.
A strategy for limiting the yield-reducing effects of corn nematodes is to protect the developing root system to prevent the stunting and early season injury associated with corn nematodes.
Corn nematodes are much more mobile than soybean cyst nematodes, which form cysts that typically stay in the upper soil profile.
Corn nematodes are much more mobile than soybean cyst nematodes, which form cysts that typically stay in the upper soil profile.
Corn nematodes will go fairly deep (18 inches or more) into the soil profile during the period of the summer when soils tend to dry near the surface. This is an important factor to consider when scouting and sampling for the presence of yield damaging levels of corn nematodes.
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Late-season scouting and soil/root sample submission for nematodes may show lower than actual levels of nematodes.
Root parasitic nematodes commonly found in corn are very small and range from 0.25 mm to 3.0 mm in size. These nematodes can be further classified by feeding habits and described as ectoparasites, which remain on the outside of the root and feed or endoparasites that penetrate the root and enter the root to complete their life cycle.
Common above-ground symptoms in corn include thin stands, stunted plants, uneven tasseling, leaf yellowing, and eventually small ears and kernels. Root symptoms include swollen roots, root branching, lack of fine roots and small patches of dead tissue on the root systems.
Plant symptoms aren’t specific to corn nematodes and further analysis with plant and soil testing may be required to confirm presence. A few of the nematodes common to the Midwest and important to corn production include: dagger, lance, lesion, needle, stubby root, and stunt nematodes. Damage can be moderate to very damaging depending on cropping history and soil types.
After nematodes are discovered and typed, it’s important to consider control practices prior to the next corn crop. Fields should be maintained with good fertility. Pay attention to micronutrients on coarse-textured soils. Weeds must also be controlled due to the nematodes’ ability to feed on other plant roots.
Rotate your nematode trouble spots away from corn. Keep in mind many of these species also feed on soybeans, so consider forages and small grains in the rotation. Chemical control such as Counter insecticide applied at planting or nematicides cleared for control of nematodes in corn.
In many cases, you may want to seek the advice of an experienced agronomist or ag Extension personnel to help with diagnosis and control options.
