Insect pests can be conveniently divided into chewers and suckers. The chewers have mandibles and include stem borers, foliage eaters, leaf skeletonisers and root eaters. Examples are beetles (and their larvae), caterpillars, grass hoppers and millepedes. Suckers have a probiscis which they stick into the plant to suck sap. They include bugs, aphids, mites, thrips and scale..
The foliage chewers are susceptible to stomach poisons and repellents and to increasing predation by providing habitat. They may also be picked by hand in the garden or shaken and vacuumed in largerscale applications. Underground and boring pests are more difficult, and may only be controlable by organic methods for the part of their life cycle when they are dispersing.
Plant suckers affect plants by reducing their vigour and may spread viral and bacterial diseases. In conventional control they are treated by systemic sprays, but these are not available to the organic farmer. They can be smothered and abraided, physically removed by water jets and suction, trapped and may also be susceptible to bird and insect predators. They may also be controlled with contact poisons.
Control of an insect pest may require holistic change in management of the crop and may need to be applied to a part of the life cycle which is not directly affecting the crop.
Black beetle pests in roots can be managed by changed irrigation. Deep watering, which fills the soil surface pores for some time, may drown some and force others to the surface where they are taken by predators. Time irrigation so flooding coincides with the early morning feeding routine of local birds, and some useful control can be obtained. Frequent shallow watering encourages this pest.
For any fruiting vegetable in fruit fly areas or for cabbage moth on brassica, light mesh covers and be used for total exclusion of the adult stage. These covers are tough and reuseable and surprisingly do not inhibit growth of a tough plant such as capsicum or broccoli.
There are many plant extract poisons which are made by organic growers. They include nettle, rhubarb, tomato leaf, capsicum spray, neem leaf and many others. The commercially available ones include knockdown (contact) poisons such as pyrethrum and stomach poisons such as derris. Certified organic growers may only use pyrethrum without the piperonyl butocide synergist and users of either chemical should be aware that they are toxic to humans and fish and may be toxic to some beneficial insects too. Any targeting of the sprays will help reduce unwanted kills. Spraying the underside of leaves, time of day of pesticide application or applying the spray only to the ground surface and stem in the case of insects which hide below the soil during the day and climb to feed at night.
Other sprays include lime (burning action), suffocaters (kaolin and flour-milk glue) diatomaceous earth (dehydration) or cuticle destroyers (potassium soap) and communication disrupters such as pheromones or "bug juice" sprays.
Providing habitat, such as rags tied around told hessian sacks on the surface, for the many insects which retreat during the day, is a good way to concentrate the population and target any sprays used. In the garden just toss the sacks into the fowl yard and let them enjoy a feast.
Don't underestimate the insecticidal power of simple sprays such as garlic. It is not just a repellent, it can kill, especially small soft bodied bests. Most home made sprays are not sieved or filtered well enough and block most apparatus. Simple hand pumps or power units capable of handling some slurry are necessary for home made sprays. The commercially available sprays are generally very good and cause no blocking of nozzles.