Introducing a natural predator that will attack one type of pest without harming another is called biological control. Many large-scale commercial food and plant producers are using biological controls instead of chemicals, with such success that gardeners are taking up the idea too. Such controls are mostly available by mail order. One of the most common is the nematode, a tiny parasitic worm used against slugs and vine weevils.
Most biological controls are best used in a protected environment such as a greenhouse or conservatory. Do not use chemical sprays as well or you will kill the introduced predator.
Biological controls are perfectly safe to use and extremely effective, provided that you follow a few rules. The environment needs to be reasonably warm—but the minimum temperature requirement varies according to the type of predator. As soon as you notice a growing pest population, introduce the predator. Once all the pests have been consumed, the predator will die out and you will have to reintroduce it for any future infestations.
Make sure that you use the correct predator for each pest.
- The tiny but effective parasitic wasp called Encarsia formosa for whitefly.
- The predator Phyoseiulus for red spider mite, a nuisance in conservatories.
- Australian ladybird beetle (Cryptolaemus) for mealy bugs.
- The predatory midge Aphidoletes aphidimyza for greenfly, blackfly and other aphids under cover in a greenhouse or conservatory.
- The predatory midge Metaphycus for scale insect.
- The miniature mite Amblyseius cucumeris for thrips.
- The bacterium Bacillus thuringiensis for cabbage white caterpillars.
With these tips in mind, you'll use less chemicals in your garden while still being able to effectively control unwanted pests.
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Nematodes are commonly used to control slugs and vine weevils in the garden.
