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: A number of organophosphate and oximecarbamate nematicides were developed in the 1960s, which had the advantage that application was relatively simple (Wright, 1981). As a consequence nematicide use became more widely practised. These compounds (Table 1) are active at dosages of 2 to 10 kg a.i./ha which are smaller than the 200 to 300 litres/ha required for treatment with liquid fumigants. Most of the early formulations of these products were as granules that, when applied to the soil surface (or preferably incorporated in the top 10 cm of soil), release the active ingredient, which is spread through the soil by rainfall or irrigation. The efficacy of soil penetration depends on the amount of moisture, organic matter and soil structure. 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.