Nematodes are part of nature and part of the “rhizosphere,” which is another word for the world beneath our feet that we refer to as “the soil.” All nematodes are not bad guys, since some of them perform beneficial tasks much like the beneficial insects we have come to accept as part of the above-ground environment.
Some nematodes are very destructive in certain crops. Two of these that are common in our area are the reniform nematode and to lesser degree the root knot nematode.
The soybean cyst nematode was at one time very destructive to soybeans in this area, and it has the potential to return as an important pest. Several others are important in certain situations such as turfgrass management.
The reniform nematode is the most destructive to crops in our area, mainly affecting soybean and cotton among the agronomic crops, but also damaging several horticultural crops. Root knot nematodes are very destructive as well, but are present mainly in certain localities. We refer to the crops they live on as “hosts” since nematodes are able to actively feed and reproduce. A good example of this is cotton since reniform nematodes can increase in cotton by as much as tenfold in one season. Root knot nematodes also cause significant yield reductions in cotton in some areas.
Non-host crops like corn, grain sorghum and peanuts are not hosts for the reniform nematode may help reduce their numbers. We also have other plants, particularly some of the winter weeds like henbit that are host plants for this and other nematodes. These non-crop plants allow nematodes to survive and expand during the winter months, especially during some of the milder winter weather we have experienced in recent years.
In the past we have used some very dangerous pesticides for the management of nematodes. I use the term “management” intentionally since these materials were not capable of getting rid of nematodes, but were able to suppress them well enough to reduce their damage to crops. Most of these materials have been removed from use because of the high degree of liability connected with their use. We now have only the practices of crop rotation, fallowing, and in some cases cover crops as methods for nematode management. Soil fumigants are also used in some cases, but this method is very expensive, requires specialized equipment, and is harmful to many beneficial soil organisms.
There are now being introduced a few biological products that are able to suppress the activity and reproduction of some of the more destructive nematodes. This subject is still somewhat controversial in light of the fact that for many years claims have been made about biological materials that had little or no effect.
These newer biologicals have been shown to have promise of activity on some of the more destructive nematodes and in some cases insect pests and plant diseases. Their mention is still controversial since the academic community has not accepted them fully. Some are plant extracts such as from the neem plant. Others are extracts from marine organisms, and take advantage of enzymes present in them. Still others are combinations from these sources. Other issues such as the methods of formulation may influence their activity in some cases. These and other means of dealing with nematodes promise to become important tools in the arsenal of control measures in the future.
My suggestion is that growers become aware of these options that may soon be on the cutting edge of crop management