Insect control without using chemicals.
There are two main ways to try. One is attracting more of the naturally occurring enemies. The other is to purchase these natural enemies from a commercial producer.
These strategies are not exclusive and should be used in combination whenever possible.
Many species of birds are predators of various pest insects. The birds in turn can be attracted to the garden and pest infected area in particular by supplying water and shelter for them.
Bird baths, nesting boxes, seed producing flowers, like Sunflowers, Zinnias and Asters along with berry producing shrubs like Cornus, Berberis, Cotoneaster, Ivy and Mulberry will attract birds to the garden.
Setting an old clay pot in a damp spot of the garden will give shelter to toads. Beetles can be expected to take an interest in stones and small rocks in borders and wasps can be encouraged to nest if there is shelter and water available for them.
Natural enemies can be purchased for introduction into the garden or greenhouse. Ladybirds to control aphids, mealybugs and scale insects. Parasitic wasps can control over 150 species of caterpillars and thrips. The whole list of nematodes, to control slugs and weevils plus the Encarsia formosa for white fly are available from "Organic" suppliers like Green garden and Defenders
Mechanical control means that you use a device to exclude or reduce the numbers of pests. It includes barriers, traps and even hand picking.
Hand picking and crushing might sound unattractive but it is effective on small numbers of some pests like caterpillars and some beetles. The insects, soft bodied ones especially, can be removed by a forceful jet of water, picked up and dropped into boiling water or a strong salt solution to kill them.
Horticultural Fleece, usually white and lightweight (17g/sq.m), can be an effective physical barrier to all insects, but ensure that it makes a complete surround to the plant or plants. Fleece used over carrots needs to be flat on the soil to stop carrot root fly for example. A 14" barrier would have the same effect. Fleece used in the doorways and windows of a greenhouse or shed, needs to be fastened on all sides to be totally effective, but it does mean that the ventilation is usually better and that non pollination is the order of the day for show specimens.
Sticky tape around trees acts as a barrier for trunk climbing caterpillars and insects.
Sticky pads, either yellow or blue are used extensively in the commercial sector for catching flying insects. Fly papers will do a similar job in the conservatory, maybe not as effective as the yellow ones but more in harmony with the surroundings.
Pheromone traps are a good method of monitoring and controlling some insect pests. A pheromone is a chemical "message" used by some insects to communicate with each other. A principal use is as a sex attractant, and enables the female to attract males of the same species for mating. The pheromones can be produced synthetically and used to bait traps to capture the male and disrupt the reproduction cycle.
Cultural control of the crop as practised in crop rotation is one of the most widely used methods.
Pruning, thinning and debris control are others. The husbandry hygiene side of gardening can not be stressed too much. A clean and tidy greenhouse and garden will have less risk from pests and diseases than one left to just nature to look after.
Use strong plant material that has a built in disease resistance if possible, and don't plant related crops in the same spot year after year.
Deep Autumn cultivations will bring to the surface soil pests for the predators to dispose of and bury too deeply others that might emerge in the spring.
Where possible look to help maintain the balance that nature has to, to check the domination of any pest or disease over another.