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.

MOBILITY OF PRATYLENCHUS PENETRANS & DITYLENCHUS DIPSACI:

TIME FOR PARALYSIS TO OCCUR (HOURS):

CONCENTRATION (PPM)	P. PENETRANS	D. DIPSACI
100	1	1
10	1	5
1	5	1
0.1	48	504

INHIBITION OF MOBILITY IS REVERSIBLE IF NEMATODES ARE TRANSFERRED TO WATER

This data developed by the manufacturers of Nemacur (fenamiphos) illustrates the nematistatic effect for lesion nematode, Pratylenchus penetrans, and stem and bulb nematode, Ditylenchus dipsaci. As the concentration increases, it takes less time for paralysis to occur and, once paralyzed, if nematodes are placed in water, the effects are reversible.

TIME FOR MORTALITY TO OCCUR (DAYS):

CONCENTRATION (PPM)	P. PENETRANS	D. DIPSACI
100	5	21
10	12	41
1	27	65
0.1	57	105

On the other hand, if nematodes are left at the same concentrations for a long enough period of time, they will eventually die.

EFFECTS OF TEMIK ON NEMATODE BEHAVIOR:

BEHAVIOR	H. SCHACHTII	M. JAVANICA
	CONCENTRATION (PPM)	CONCENTRATION (PPM)
HATCHING SUPRESSION	0.48-4.8	4.8-48
HATCHING STIMULATION	--	0.48
MIGRATION INHIBITED	1	1
INFECTION INHIBITED	1	1
ATTRACTION OF MALES TO FEMALES INHIBITED	0.01	--

At UC Riverside, Anton Hough conducted a series of experiments exposing sugarbeet cyst nematode, Heterodera schachtii and root-knot nematode, Meloidogyne javanica, to sublethal concentrations of Temik (aldicarb). Depending on the concentration, egg hatch could either be suppressed or stimulated, and migration, infection, and attraction of males to females could be inhibited.

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