ABSTRACT
Nematodes cause about $100 billion of losses to world agriculture annually (Sasser and Freckman, 1987). They often do not provide the clear symptoms that aid growers to identify the diseases they cause (Atkinson, 1996). One consequence of this is that the world nematicide market is only $700 m/year (Williamson, 1995). Other factors also ensure that the nematicidal market underestimates the agricultural importance of nematodes. They are the most environmentally damaging of all crop protection chemicals. This discourages some use both from grower preference and from government restriction. Environmental harm is a risk because the nematicide is incorporated into soil to ensure its distribution to the relatively immobile nematodes. Such procedures represent an environmentally unacceptable method of pesticide application. In addition, many nematicides have been shown to cause environment damage. For instance the Montreal Protocol calls for the withdrawal of the soil fumigant methyl bromide from agricultural use by 2005. It is considered a major cause of ozone layer depletion. The USA intends to eliminate its agricultural use of the compound by 2002 unless this intention is reversed as the result of lobbying by some growers (Pearce, 1997). Other halogenated hydrocarbon nematicides are also severe biohazards. Use of dibromochloropropane (DBCP) is declining and considerable safety precautions are in place in countries such as USA where some applications remain. However, investigative journalism has uncovered cases (Jenkins, 1996) where such precautions are inadequately enforced in the developing world. For example, safety equipment is often not used during nematicide application. Such misuse is highlighted by class actions in USA courts. They have been brought against chemical manufacturers by agricultural workers from Central America. The allegations arise from ill health resulting from exposure as agricultural workers (Anon, 1992). Industrial accidents have also occurred during nematicide manufacture. The most severe incident was the Bophal disaster in India but other chemical plants have had industrial accidents. Aldicarb is a widely used oxime carbamate nematicide but there are considerable concerns about the potential toxicological hazards of this compound (Gustafson, 1993). It is detectable in groundwater after application in sandy soils and its use is closely monitored by several governments. Consequently, it has been withdrawn from many states of the USA. Nematicides are currently essential for economic production of some crops. However, they are likely to be increasingly viewed as the approach of last resort unless more environmentally benign compounds are developed.
