Pesticides are designed to kill pests, but broad spectrum application means that they also come into contact, either directly or indirectly, with natural enemies according to NSW Department of Primary Industries (DPI) researcher Marilyn Steiner.

'These may be playing an important role in regulating the target pest or other pests in the crop.

'In greenhouse crops, the natural enemies are generally paid for and released, so incorrect use of a pesticide can not only negate a bio-control program but waste the grower’s money,' she said.

Ms Steiner said in field crops, preservation of natural enemies, both within and around the crop, could be very important for an Integrated Pest Management program designed to reduce the use of pesticides.

'Knowing which pesticides are safe to use when natural enemies are present is therefore very important in both situations,' she said.

Some information on side-effects is available through biocontrol suppliers such as Koppert (http://www.koppert.nl) and BioBest (http://www.biobest.be), and through members of Australasian Biological Control Inc. and their publication The Good Bug Book (http://www.goodbugs.org.au).

However, Ms Steiner said there were many gaps, particularly with regard to the effect of pesticide residues.

'Local knowledge is also important to make information relevant to Australian conditions,' she said.

As part of a three-year Horticulture Australia Limited funded project to be completed this year, Ms Steiner, fellow researcher Stephen Goodwin and Senior Technical Officer Tony Wellham are examining the residual effects of eight greenhouse pesticides on commonly used biocontrol agents.

The pesticides Talstar (bifen-thrin), Lannate (methomyl), Nitofol (methamidophos), Pirimor (pirimi-carb), Vertimec (abamectin), Dithane (mancozeb), Success (spinosad) and Confidor (imidacloprid)) were applied to the foliage of three different crop plants (cucumbers, tomatoes and basil), which were then maintained in glasshouses.

Negative effects on the natural enemies Phytoseiulus persimilis, Typhlodromips montdorensis, Aphidius colemani and Encarsia formosa were monitored during a two-week period by exposing the bio-control agents to progressively aged residues on leaf discs cut from treated foliage.

Three of these pesticides (Talstar, Pirimor and Confidor) were also applied as media treatments to assess the effect on the ground dwelling predatory mite Stratiolaelaps scimitus (Hypoaspis), which feeds on fungus gnat larvae.

The plants were grown in six different media - coco peat, sawdust, composted bark mix, perlite, rock-wool and vermiculite.

Presently, the pesticides with the longest residual effect are being tested as spray applications to plastics used on side walls and floors.

Ms Steiner said some interesting results have resulted from the trials.

'At the end of the day we hope to compile information arising from our trial results and also put together overseas data as a handy reference for growers, to enable a more informed choice of pesticides.

'In the interim, it is safest to remember that the less pesticide used, the less likelihood of a negative impact,' she said.

Contact: Marilyn Steiner, NSW DPI, Gosford, (02) 4348 1915.

This story appears in Agriculture Today.