Title: Chemical control of nematodes: efficiency and side-effects
Headings: Chemical control of nematodes: efficiency and side-effects
Chemical control of nematodes: efficiency and side-effects
S.R. Gowen
Introduction
Chemical control of nematodes
The demand
Efficacy
TABLE 1
Nematicides currently available on world markets
TABLE 2
Examples of recommended nematicidal dosages and treatments for some important crops1
Side-effects
Future developments
References

Content: Heavy soils with relatively small pore spaces are more difficult to treat than sandy soils which have larger pore sizes. Some chemicals, particularly the organophosphates, are absorbed in organic matter, in which case efficacy may be impaired (Bromilow, 1980). In general, distribution of the active ingredient or its toxic degradation products is less efficient than that of fumigants and results with granular nematicides have sometimes been inconsistent. To be effective, nematicides have to persist long enough for nematodes to be exposed to lethal concentrations, which may be as low as 1 to 2 m g/litre. Extended persistence is, however, not desirable if there is a risk of residues in the crop or the active compounds contaminating groundwater. Persistence of soil-applied nematicides depends on the soil characteristics. In warm countries, relatively high soil temperatures may accelerate the natural degradation of nematicides, and in protected crops where even higher soil temperatures than out-of-doors may occur, the effective life of a nematicide might be as short as one to three weeks (Bromilow, 1980). The repeated use of products of similar structure can lead to the selection of a soil microflora that metabolizes these compounds and decreases their persistence. Side-effects
All nematicides are eventually degraded if they remain in the topsoil where there is greatest microbial activity. Once nematicides or their degradation products are flushed through the upper soil layers their persistence may be extended.