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Pest and disease control 101: helpful hints for vegetable gardening

Keeping pests and diseases under control means a lot more than grabbing for a chemical spray - especially if you're an organic gardener. I've already raved on about why organic is better and why you should ditch chemical gardening practices. It's better for your soil, it's better for your little micro environment, and of course, it's better for you.

So how do you achieve this organic bliss? The answer is easy - instead of fighting nature, make nature work for you. It just requires a little planning beforehand.

Pests and diseases can be combated in the organic garden by breaking reproduction cycles, confusing pests - which keeps them away from your garden, getting good insects to eat your bad insects, getting other animals to eat your pests, and making your vegies and fruit unpalatable to pests.

We've titled this article 'Pest and disease control 101' as it introduces the basics. A supplementary article, 'Pest and disease control 202' is shortly on it's way and will go into details for specific symptoms and solutions.

Crop rotation

Cutting a long story short crop rotation is about moving your vegetables around your little patch each year. This way not only do you give your soil a rest from having specific nutrients depleted each year, you also help break the reproductive cycle of soil borne diseases and some pests (eg nematodes).

This is an important enough topic to warrant its own article, so you'll find more specific and practical info on our crop rotation page.

Companion planting

This is another one of those little organic miracles. By planting certain vegetables, or herbs, together you can ward away pests, plus boost your garden's growth.

One of the best known examples is planting onions and garlic with carrots (the allium's smell confuses pests, keeping them away from your carrots). Any organic vegetable gardener should make companion planting an important part of their planning. Again, for more detailed information see our companion planting page.

Don't reintroduce disease back into your garden

This sounds pretty obvious but it's amazing how many gardeners slip up. Organic gardeners get fanatical about our compost - it's fantastic stuff, full of basic elements and packed with micronutrients and micro-organisms. But make sure your never put diseased plants in your compost bin or heap. All you'll end up doing is bringing the disease back into your garden. So toss diseased plants in the bin instead.

Beneficial insects

Get rid of bad insects with good insects. Confused? Don't be. There are many insects you can encourage into your garden that pray on pests, or use pests as the host for their young.

To get them into your garden try growing herbs with umbrella-style flowers like coriander, fennel, parsley and Queen Anne's Lace. Their flowers attract parasitic wasps (good wasps) that like laying their eggs into grubs, aphids and other pests in the garden. The eggs hatch, and the larvae feast on the host. Gruesome sounding stuff, but use it to your advantage.

These flowering herbs will also encourage ladybirds, which also enjoy chewing on aphids. If you sow your beneficial herb mix but still don't get any good insects, you might need to buy them in, try mail order, the Internet or even some nurseries.

Other beneficial friends

You can also keep down the number of insects in your garden with other animal friends. If you've got chickens or ducks you let them loose into your garden and can just about guarantee you'll have no snails or slugs left. Plus they'll dig up and eat other insect eggs on or just under the soil. But keep on eye on your feathered friends, as they'll start into your vegies too if you're not watching!

Or try turning to your natural environment and build a frog pond. Native frogs and toads (not cane toads - for the Aussie audience) can make their way into your vegie patch where they'll feast on your insect population (indiscriminately though!) But you can't go past their croaking in summer storms, or finding an amphibian acquaintance when you're out harvesting.

Pyrethrum - the big organic gun

When you want to indiscriminately (but organically) kill bugs you can't go past pyrethrum sprays. A sweet smelling flower extract (bought from nurseries) it should only be used on pests that you know (we've used it on aphids when our ladybird population was low).

But be warned, pyrethrum residue lingers for a number of weeks, so it can also kill beneficial or neutral insects that come by.

Deter pests with organic sprays

If you don't want to kill everything organically using pyrethrum, you can always deter plant eating pests using handmade organic sprays.

These are aimed at any leaf eating insects - grubs, caterpillars, grasshoppers, snails, slugs, etc, for almost all plants.

The idea is to create a foliar spray that will make the plant taste so terrible, the pests will go away and annoy your neighbours, leaving your vegetable patch alone. Not nice for your neighbours, but hopefully this'll help you convert them to organic gardening!

Try mixing water with either (or a mix of) crushed garlic, chilli (hot pepper) or onion. You might need to water it down a bit, otherwise it might be so strong you mightn't want to eat your homegrown vegetables either!

Other gardeners swear by a mix of kelp (to help the vegies grow strong and fast) and neem oil - which apparently tastes terrible. Neem oil is an concentrated extract from the neem tree, native to India. We're currently trialing this spray in our garden, so we'll let you know how well it goes in the coming months. The only bad thing I can say about it at the moment is that it is not cheap. I guess we'll soon find out if you get what you pay for!

Don't forget with any spray you'll need to reapply it after rain, or if you water overhead with a sprinkler.


Last updated 23 October, 2008

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