By Bob Kemerait
Plant-parasitic nematodes affecting our row crops are undermanaged, especially in corn. As for all row-crops, the symptoms of damage from nematodes in a field may be incorrectly dismissed as poor soil fertility or just "sorry dirt". Corn growers who detect areas of poor growth in their fields should submit soil samples to a testing lab for nematode analysis.
Another reason for confusion is the long-held belief that the root system of the corn crop is simply too robust to be affected by nematodes. This point is still debated among Extension specialists from across the country in reference to the need for nematicides to protect the crop.
Drawing specifically from my Extension program at the University of Georgia, where producers in our state aggressively support research nematodes through the Georgia Commodity Commission for Corn, nematodes do cause significant damage in corn production and they can cause significant losses in yield. Additionally, use of appropriate nematicides can improve yield by anywhere from 5 bushels to 40+ bushels per acre.
The potential for significant increases in yield include the type of nematodes in the soil, the size of the nematode populations, the type of nematicide deployed, use of irrigation and weather conditions during the season.
The corn crop in the southern United States is affected primarily by three nematodes: the southern root-knot nematode, the peanut root-knot nematode and the stubby-root nematode. The presence of sting nematodes, though much less common, can be devastating in some fields. The populations of these nematodes increase when corn is planted behind corn, or in rotation with soybeans, cotton and to some extent peanuts.
Growers can reduce nematode populations by extending the time between corn crops. Ideally growers would plant a crop that is not a host to the same nematodes as those that affect corn; however this is difficult. Though we do not have any corn hybrids with resistance to parasitic nematodes, such resistance is available in peanut ('Tifguard') and partial resistance is available in cotton, such as PHY 367WRF, ST 5458B2RF and ST 4288B2R, and in a number of soybean varieties. By planting such peanut, cotton and soybeans varieties before a corn crop, growers can reduce, but not eliminate, populations of nematodes that will affect the corn.
Parasitic nematodes tend to be larger in reduced-tillage systems than in conventional-tillage systems. This is likely because of the disturbance of nematode populations in the process of deep-turning a field in conventional systems.
Growers currently have four products for the management of nematodes in their corn crop. These include fumigation with Telone II (3 gal/A), use of the granular insecticide-nematicide Counter 20g (unless Accent herbicide is used), the seed-treatment nematicide AVICTA Complete Corn and the biological VOTiVO. Fumigation with Telone II has the potential to produce the greatest increases in yield where nematode populations are especially damaging.
Where nematode populations are less severe, perhaps considered to low-to-moderate, use of Counter 20G and AVICTA Complete Corn protect yield potential. Though not a "stand alone" product, use of the biological product VOTiVO may enhance management of nematodes.
In a recent trial, use of Telone II increased corn yields over the corn not reated with a nematicide by 19 bushels per acre. Use of Counter 20G increased yields by 8.5 bushels per acre.
Kemerait is a plant pathologist with the University of Georgia Cooperative Extension.