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Introduction to chemical use

Many chemicals are hazardous to beneficial insects and predatory mites. Care must be taken in the choice of products and the timing and frequency of application.

Good populations of beneficials typically enable reductions in chemical use with all the benefits that this brings - less environmental impacts, less exposure for the farmer, fewer problems with withholding periods and residues and less disruption to neighbours.

In recent times a number of "soft" biological and chemical insecticides have become available and these have made it much easier to incorporate beneficial insects into IPM programs. In this way, natural enemies can make a useful and often major contribution to pest management. They also reduce reliance on insecticides and become an important tool in resistence management.

Broad spectrum pyrethroid, organophosphate and carbamate insecticides are generally "highly" or "very highly" toxic to beneficial insects (although there are some exceptions) and should be avoided if possible. Applications of these products may severely reduce numbers which can take many weeks to recover.

Although beneficial insects are sensitive to many chemicals they are often found in crops that have been sprayed with "hazardous" chemicals. How have they survived? Many beneficials have a phase where they are more protected - for example, predatory mite eggs may be laid on the underside of leaves against a leaf vein where spray contact may be reduced. Many developing parasitioids are protected by the body of their host. And ladybirds in the pupal phase may also be protected to various degrees. By the time of emergence the insecticide residues may have dispersed.

If spraying is not done repeatedly then recovery does occur and sometimes quickly - depending on the situation. For instance, residues from chemicals in protected crops may take months to disperse while those in fast growing outdoor vegetable crops may be gone in a week. Ladybirds may take longer to recover than Trichogramma wasps if there was lots of parasitism before the spray.

Applied = toxicity of chemicals when sprayed on the beneficials in the field. The rating is a general overall toxicity allowing for the impact on the population of the beneficial.

L = Low toxicity = nil or low impact on beneficials.

M = Moderate toxicity = beneficial activity significantly reduced but can recover in a week or so.

H = High toxicity = a high proportion of the beneficial population is killed and re-establishment will not be possible for several weeks.

( ) = estimated toxicity, based on anecdotal information and known impact on similar organisms.

Residual = suggested waiting time (in weeks) after application of the product before introducing beneficials. In protected crops this period may be much longer.