TROPO's Organic Info Library

Strategies for organic pest management

Knowing what's happening in your paddock or orchard is a key to successful organic pest management, according to TAFE lecturer Dave Forrest, speaking at a very successful TROPO field day on organic pesticides.

Here are some of the important points he made, compiled by Graeme Eggins.

Growers who try to understand the ecology created by their planting will then know how to use less pesticides more effectively. But just because a pesticide is made from natural sources does not mean it is safe to use indiscriminately.

The aim of organic pest management is to grow crops under conditions where pests are controlled by a combination of factors, not just spray programs.

Organic farming does not aim to kill pests entirely, but to reduce their impact to an economically acceptable level.

When farmers plant a crop they also provide food and a place to live for pests and predators. The usual sequence is that pests take up residence first, attracted by the plentiful supply of food the farmer provides. They are followed by predators, attracted by the pests on which they can feed. Parasites that prey on the predators are usually last to arrive.

This situation means that a grower who wants to set up an effective pest control system needs to be able to recognise the "goodies"and "baddies" in their crops - the pests and the predators. Local NSW Agriculture offices have available a range of inexpensive printed material on pests which includes photographs and drawings for easier identification. The Queensland Department of Primary Industry also produces several excellent handbooks with colourplates.

The organic farmer should also provide extra habitat for predators. In most cases, pests build up their numbers in favourable conditions much faster than do predators. So to give the predators a head start, organic farmers provide them with food (e.g. trees that produce nectar for predatory wasps) when the pest species are absent, such as over winter.

Also, growers are wise to provide trees, hedges or other cover for predators like insect eating birds to shelter in close to the crops. (See Windbreaks section .)

Dave Forrest also made these points :

Microbial controls are available that are not toxic to the environment. These include bacterial insecticides such as Bacillus Thuringiensis (BT), sold under various trade names including Dipel (see separate page on organic pest control products). Local growers have used it to get good control on twig girdler in macadamias, though native parasites give about 50 per cent predation.

Currently some researchers are looking at biological engineering of the BT bacteria to increase its effectiveness. This follows some reports of BT resistance in the Lockyer Valley of Queensland and elsewhere.

Macadamia growers have said BT mixed with a carrier like Codacide Oil gives them "fairly good" control of nut borer, provided it is applied at the right time. The young borer has to be caught before it disappears inside the nut.

Insect eating nematodes could well be the pest predators of the 2000s - effective but kind to the environment . Research in the US has shown that they attack more than 230 species of insects. The nematodes enter by the mouth parts or spiracles. Once inside the body cavity, the predators feed on the intestinal wall of their host. They release a bacterium in their faecal matter which mummifies the insect while the nematode feeds and reproduces inside it. Stricken insects usually die within 24 hours.

Some 10 to 14 days later the nematode young emerge from the corpse and go looking for a new host to repeat the cycle. The nematodes can live from 12 to 15 months in moist soil without feeding.

The nematodes, because they actively seek out their particular prey, are thus much more effective than most insecticidal sprays. Researchers say nematodes which attack hard-to-reach pests like termites, for example, could revolutionise commercial pest control.

Insect-eating nematodes are not yet available commercially in Australia although the Department of Agriculture is currently testing one species which preys on banana borers. American researchers have identified nematodes which eat fleas ants, beetles, caterpillars, weevils grasshoppers, thrips and wireworm plus bugs of all kinds.

Sprays made from natural plant ingredients such as turnips, garlic rhubarb, black pepper, chilli, neem and onions can be effective in a farm pest management plan. (See separate page for some recipes).

Pyrethrum is now widely used as a base for a number of "natural' pesticides. Dave warned that despite the fact that most organic certification groups allow its use pyrethrum is a broad range killer that should only be used as a last resort.

It is effective against many North Coast pests, including the fruit spotting bug and monolepta beetles Dave suggests that if necessary growers should spot spray with care to avoid harming helpful predators.

Other protective sprays are made from fatty acids (ie. soapy water washes), copper sulphate (to prevent fungus attacks) and various oils. The oil sprays, if applied when the young scale insects are active before they develop a hard shell, give good control of hard scale but do not harm predators like the steely blue ladybird. Dave recommended that growers use products like DC Tron or Low Vis instead of plain White Oil.

Fungistats allowable by leading organic certification groups include copper sprays and wettable sulphur Like all similar organic agents they are only protective - no curative organic fungicides are available at present.

Several organic certification organisatlons are currently reviewing copper sprays, which are allowable inputs under existing regulations. The re-examination follows reports of copper sprays being implicated in possible earthworm kills. However at this stage the evidence is only anecdotal and much research has to be done.

Aphids are more a nuisance than a real pest in most North Coast orchards: However they can spread virus diseases for which no effective organic control is yet available. As most viruses take three weeks before they are noticed, it is important that growers monitor aphid numbers, possibly using a sticky yellow coloured surface trap (Tac-Gel is one product that can be used for this purpose as well as for banding the butts of trees to prevent ants entering the canopy).

Dave said leaf miners were another minor problem. They only attack young trees and with a proper feeding program, the trees grow out of it.

Certain nematodes are more serious pests. Suggested organic solutions include raising the organic matter level of the soil, selection of non-host plants in the rotation system and soil sterilization with solarisation. (Solarisation means covering affected soil with clear - not black - plastic for at least two months in summer.)

Mites in vegetable and fruit crops are well controlled by other predatory mites, some of which are available commercially. Providing a suitable habit will also help attract predators which normally live in your area.

Fruit fly: No really effective organically acceptable control is currently available for one of the North Coast's biggest pests, the Queensland fruit fly.

Organic growers can minimise fruit fly' problems by not growing susceptible crops. However, if you do grow such fruit, maintain strict orchard hygiene.

Collect infected fruit within a day of falling. Kill the grubs either by leaving the fruit in a clear plastic bag in the sun for a week or more, or by drowning it in a drum of water. Infected fruit also can be put in a compost heap to "cook" but only if the heap is really hot.

Chickens and other poultry free ranging under orchard trees will also help break the fruit fly life cycle by eating grubs as they emerge from fallen fruit. (A TROPO member said guinea fowl are the best scavengers, although they are inclined to wander and make a racket at dawn.)

Lennox Head orchardist and TROPO member Anders Lindstedt is currently developing an electric fruit fly "zapper" and studying other methods for trapping these pests. One obstacle is that the most reliable attractant (pheromone) attracts male fruit flies only, while it is the female flies that actually damage fruit. However Anders suggests that decreasing the number of male fruit flies plus a possible confusion effect from the pheromone may be effective in reducing his losses to fruit flies.

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