ORGANOPHOSPHATES AND CARBAMATES: NEMATISTATS OR NEMATICIDES:

Nematistat is a term coined by nematologists to describe effects which have been observed when nematodes are exposed to low concentrations of organophosphates and carbamates. These products do not always kill nematodes, but at times appear to disorient, paralyze, or confuse nematodes and so prevent infestation of roots. If the product is present for a long enough period of time, the nematodes will eventually starve to death. In practical application, the product decomposes in soil over a period of several weeks. This can result in nematodes regaining their abilities to feed on and penetrate roots. In annual cropping situations, the goal is to achieve control for a period of several weeks so that a healthy root system develops to carry the crop thru to harvest. In perennial cropping situations, repeated applications can be timed to maximize the nematistatic effect.

Not all nematologists are believers in the nematistat effect, probably reflecting different observations in different cropping situations.

In reality, the same product could be acting as both a nematistat and a nematicide in the same situation. Keeping in mind that organophosphates and carbamates must be distributed through the soil via irrigation water or mechanical incorporation, any particular application will likely result in a range of concentrations depending on the uniformity of incorporation. In some areas, concentrations will likely be high enough to kill nematodes, while in others sublethal effects will occur.

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