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Sacrificial plants', such as nasturtiums, can be used to lure pests like these cabbage white caterpillars away from your crops

IF there is anything that characterises the organic gardener it is an approach to pest control that relies on natural methods and using nature to your advantage rather than resorting to chemical controls. However, given the huge number of ways to keep your garden pests under control, it's handy to get an overview of what the organic gardeners' arsenal has to offer so you can pick the right method for your particular problem.

"Prevention is better than cure" is the mantra of organic pest control and most of the work you put in to your garden should be about avoiding infestations rather than treating them. Healthy plants can, more often than not, survive pest attacks well but sickly plants will not win the battle. Healthy plants start with healthy soil. It cannot be underestimated how important your soil can be in giving your plants a head start in the fight against pests. Garden compost and leafmould are the best soil conditioners and fertilisers as they feed the soil rather than the plant. Quick-fix artificial fertilisers are designed only to feed the plant and too much fertiliser can make your plants tender and nitrogen rich - just the way the pests like them. So to ward off attack it's best to start from the ground up for stronger growth and better pest resistance. A yearly crop rotation in the kitchen garden will help to keep one step ahead of soil-dwelling pests as well as diseases and will also help keep your plants healthy by allowing you to give them the best soil conditions. Hygiene is key in the organic garden. Try to keep things tidy enough that there are few places for unwanted pests such as slugs and snails to hide but make sure to leave suitable homes for insects which help control pests (more of which later). Also, give your greenhouse a good clean down every year to catch out any pests hiding there. The number of resistant vegetable varieties available is always on the increase and choosing these can be very valuable keeping crops in peak condition and in controlling pests, especially where you have a particular problem. Try root aphid resistant lettuces such as Milan', soil-dwelling slug resistant potatoes such as Cara', Desiree', and Romano' and carrot fly-resistant carrots such as Fly away'. You can also try including "sacrificial plants", such as nasturtiums, in with your crops as pests may chomp on these rather than your vegetables.

As the next line of defence, barriers are best for preventing pest damage. These must be in place before pests have a chance to attack if they are to work properly so using them at the sowing or planting-out stage is generally a good plan. A cover of fine horticultural mesh over vegetable crops will stop most flying pest types and can be useful to protect carrots from carrot root fly, cabbages from cabbage white butterflies, birds, flea beetles, and white fly and peas from pea moths. Other less general barriers can be used to protect specific plants. Bottle cloches can be made easily by cutting the bottom off plastic bottles and can protect most plants from slugs and snails and stop cabbage root fly from laying their eggs at the base of young cabbage plants. Netting can provide protection against birds for your fruit and vegetables and can also stop cabbage white butterflies from laying eggs on brassicas crops. A cover of small-gauge chicken wire can also stop mice getting to peas sown direct into the soil. Many barrier types are also available specifically to hamper the progress of some of the worst all-round culprits - slugs and snails. Try gravel, mineral granules or egg shells sprinkled around plants as these provide an uncomfortable surface for slugs and snails to cross, either by being sharp or by sucking up moisture. Repellent sprays are available made from yucca plant extract. These can be sprayed around plants to deters slugs and snails and are useful to prevent them entering via greenhouse windows. Copper tape forms a great barrier as it gives off a natural electric charge which these molluscs detest and it can be placed around pots and the legs of greenhouse staging. Slugs love to eat bran but it swells inside them reducing their appetite and hopefully putting them off eating your plants so sprinkle it around tender and newly planted crops.

There are quite a few useful ways to trap pests including many homemade ones. Try beer traps for slugs by burying shallow containers in the vicinity of vulnerable crops. These should have a 2cm rim above the soil level to discourage beetles and other creatures from falling in and should be filled with beer which slugs can't resist. You can also trap slugs and snails by making temporary shelters for them out of roof tiles or grapefruit skin halves. These can even be baited with comfrey leaves or lettuce and should be checked everyday to collect the unfortunate residents for your disposal method of choice. Sticky traps and pheromone traps are commonly available to prevent codling moth damage to apple trees or plum moth damage to plum trees. These can be hung in the trees outside. You can also hang yellow sticky traps in the greenhouse to catch white fly.

Use the wildlife in your garden to your advantage by encouraging insects and other animals that predate upon pest species. It's easy to encourage more of these by planting some annual flowers such as marigolds and Californian poppies or perennials such as hardy geraniums in the kitchen garden. This will look pretty and attract valuable insects such as hoverflies and ladybirds who like to eat aphids. A bird feeder is great to get birds visiting more often and helping to pick off pests from around your plants. If you have space, a pond is a wonderful wildlife attractant especially for frogs who like to eats slugs and snails. Leaving some areas of the garden undisturbed and providing piles of twigs and logs also gives a home to insects like ground beetles, spiders, centipedes, and harvestmen who all devour garden pests.

Another way of using nature to fight your battles for you is to try out biological controls. These are predators or parasites of common pests which are bred in high numbers and introduced to indoor or outdoor crops in some form of inert carrier. Many of these are now available to buy commercially and can be used to treat a variety of specific pest problems. The microscopic nematode Phasmarhabditis hermaphrodita can be used for controlling slugs though it is unfortunately not effective for snails. The nematodes generally come in a pack of moist clay which you can mix with water and apply to your soil with a watering can. These will control slugs for up to six weeks, after which you may need to reapply. Moist soil conditions and temperatures of 5-20oC are required, so this method is most effective during spring to early autumn. The predatory mite Phytoseiulus persimilis is the best biological control for red spider mite and if introduced early enough, will completely control populations by eating adults and their eggs. Phytoseiulus are usually introduced in vermiculite by sprinkling them on to the plant(s). For Phytoseiulus to do their job the temperature must be between 18-25C (64 - 77F) for at least part of the day and humidity should be kept high at around 60 per cent. As with most biological control agents the aim is not to wipe out the pest completely but to control it. It may sound contradictory, but hopefully some red spider mites will remain in the crop as these will sustain a small population of Phytoseiulus, who will be ready to take arms again if the pest population begins to expand in the future. Other examples of biological controls include the parasitic wasp, Encarsia formosa, which can be used to control white fly in the greenhouse and the parasitic nematode, Heterorhabditis megidis, which goes after Vine weevils.

Lastly, one of the best ways to prevent pest problems as an organic gardener is to be vigilant. Keeping an eye out for pests before they take hold buys you the time you need to step in and prevent serious problems. Keep an eye out for damage or actual pests and act straight away to keep them in check. Just being observant in the garden allows you to pick off many pests by hand especially slugs and snails which are best caught in the late evening. Aphids can be easily sprayed off with water or squished if they are caught soon enough and many pests can be prevented just by knowing when or where they are most likely to attack. For instance in April, check the centres of your gooseberry bushes to catch sawfly eggs and larvae which can then simply be removed before they cause any damage.

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