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Managing pests and disease

Whilst many pest and disease problems can be prevented, there are various occasions where pest or disease numbers increase to such high numbers that they can cause serious damage to your crops. It is crucial to properly identify the culprits.  It happens often that an innocent bystander who happens to be at the scene is accused of the act.  It may have been the one who has just eaten the culprit.

Mechanical control


Mechanical controls include barriers that keep pests away from your crops.  There are various types of netting available to protect your vegetables (fleece, crop covers, bionet, bird netting).  It’s important that you use the right type of netting for the relevant pests.  A net to keep the small carrot root fly out needs to be a lot finer than a net for cabbage white butterflies.


Collars are used around brassicas to prevent the cabbage root fly from laying its eggs near the cabbage stems.


Many pests can be lured into traps.  The beer trap for slugs is a popular example.  If you use this method ensure that the lip of the container is above the soil surface otherwise you may also catch some ground beetles which would have eaten many more slugs than you have caught.  Personally I can think of a much better use of beer!

You can also buy yellow sticky tape from garden centres to catch flying pests such as aphids.  They are very good as indicators to find out which pests you have but they will not control pests sufficiently.


Handpicking larger pests such as slugs, leatherjackets or caterpillars can be quite efficient especially in a small garden.  I know some  gardeners who get great  satisfaction from this.

Biological control

Biological control includes attracting beneficial creatures that feed on pests as well as introducing predators for the job!  These predators can be purchased by mail order but are generally very expensive especially for a small area.

It is much more efficient (and a lot cheaper) to attract native beneficial creatures into your garden than to purchase foreign species.

Examples of natural predators include: Hoverflies – the larvae and adult hoverfly feed on aphids. Lacewing – feed on aphids Ladybirds – feed on aphids Beetles – feed on slugs and many other small pests Earwigs – most people believe they are pests but they also feed on aphids Frogs – feed on slugs 

Chemical control

There are a number of so called ‘safe’ organic sprays available to the gardener.  They are safe in the way that they are fully biodegradable within a couple of days (with the exception of copper sulphate) but nearly all of them will also kill beneficial insects and thus disrupt the natural cycles. The garlic spray (Envirorepel) is one exception.  It only masks the smell of host plants so that pests find it less attractive or get confused.  Apparently it also strengthens the plants so that they become more resistant.

A milk/water spray (1 part milk and 7 parts water) was probably the best new discovery in organic disease control.  I have successfully used it to control diseases such as grey mould and mildew on a variety of vegetables.  You can spray it with a little plant spray directly onto affected plant parts ideally three days in a row and the disease stops spreading further.  Unfortunately it didn’t work for potato blight.

Other organic sprays include: Derris – to control aphids,  caterpillars, flea beetle Pyrethrum –  to control aphids, caterpillars, flea beetle Insecticidal soap – to control aphids, whitefly, spider mites Soft soap – to control aphids Quassia – to control aphids,   apparently safer than derris and pyrethrum Bluestone (Copper sulphate and washing soda) – to control potato blight, apple scab Sulphur – to control powdery  mildew, rose blackspot

Note: All these sprays can also damage beneficial insects or can be harmful to fish, livestock and worms (i.e. Bordeaux mix)

Home-made sprays: Home-made sprays are often prepared by hobby gardeners to control various pests and diseases.  They are illegal in the EU as they are not tested.  Some of them are extremely toxic (rhubarb spray) to all sorts of wildlife.  The most interesting spray is a compost tea or extract.  You soak one part of compost with ten parts of water for about a week and stir it daily. You then dilute it with another 10 parts of water before spraying it onto susceptible crops to prevent or halt fungal diseases.  Many scientists all over the world achieve tremendous results in controlling a large variety of diseases.  But remember you are not allowed to make it yourself.

Source: greenvegetableseeds