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Mother Nature, pest controller

A lacewing larva
A lacewing larva

Sustainable Gardening is one of the units covered on our RHS Practical Certificate courses and is probably my favourite topic – propagation being a very close second!

There are a few ‘traditional’ gardeners who lament the banning of various chemicals which were so effective at controlling our pests and diseases, but they have been withdrawn for very good reasons.

Many of them were not ‘selective’, that is they would kill not only the problem pest, but anything else that dare set foot on your plant. So the ladybird who flew in to eat our aphids was also killed!

However an even bigger problem, especially for commercial growers, is that many of our pests have very short life cycles; as little as two to three weeks for some glasshouse pests. This means many generations in a year.

In fact they can have as many generations in a single year as most families have had in the last 300 or more. Plus each ‘mother’ can pop out more babies than we would want to think about (and, in many cases, does not even have to mate first!).

So each time they were sprayed with a chemical a few would survive, or hatch out into an environment which still had some of the chemical in it. These tough survivors would breed or produce more resistant offspring. Survival of the fittest.

The traditional chemicals no longer bothered them and although new chemicals – with different modes of action – would work for a while, it was obvious this was not a long-term solution.

By the late 1970’s this was becoming a real issue, particularly for commercial growers. Consumers were also beginning to question the use of chemicals on edible crops...

Another solution had to be found, and so Biological Control was ‘invented’. In nature there is always something higher up the food chain and so we just had to find something to eat, or control our ‘pests’ in some way. The first to be widely used in glasshouses was a small parasitic wasp, Encarsia, used to help control glasshouse whitefly. Around the same time, another serious glasshouse pest, the red spider mite, started to be controlled by the introduction of a predatory mite, Phytoseiulus.

There are now many forms of biological control available, for amateurs as well as professional growers. Slugs, vine weevils, aphids and caterpillars all have their natural enemies, and we can supplement these with purchased predators or parasites.

I admit to having personal doubts about the use of some, particularly in the garden rather than in glasshouse, believing we should be wary of what we introduce and where! However, as an alternative to chemical sprays, it is a no-brainer.

Far better, especially in a garden situation, is to help a natural ecosystem develop. Most of us want to see blue tits, thrushes, frogs and hedgehogs in our gardens. And these feed on aphids, caterpillars, slugs. You can’t have one without the other!

Live and let live, and a natural balance will develop – are a few holes in your hosta leaves really that bad?

For more details on all things horticultural, including their qualifications, go to www.rhs.org.uk

- Manea School of Gardening (RHS Approved Centre). Bookings now being taken for RHS courses commencing in September. Plant sales Saturdays 10am to 4pm.

www.maneaschoolof gardening.org


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