Integrated pest management in a home vegetable garden

Chewed leaves and aphids all over the new growth send most of us straight to the shed for the strongest thing in there, and that is usually the move that makes the next few months harder rather than easier, because a broad spectrum spray takes out the ladybirds and the lacewings along with the aphids and leaves nothing behind to do the work for you. Integrated pest management is the alternative, and the name makes it sound a lot more technical than it is.

The short version is that you watch the patch, you work out what you are actually looking at, you do the cheap things first, and you keep a spray for the day when nothing else has worked. Nobody starts out knowing which grub is which, and there is no shortcut past the part where you look things up, so treat the first season as the one where you learn the cast.

Work out who is who before you do anything

Ladybirds and their larvae get through aphids by the hundred, and the larvae look nothing at all like the adults, which is why plenty of people squash them by mistake. Lacewing larvae do the same job and look like tiny alligators. Hoverflies look a bit like small wasps and their larvae work straight through an aphid colony. Learn those few, leave them alone, and a decent slice of your pest problem gets handled while you are asleep.

On the other side of the ledger, the ones that genuinely cost you a crop around here are snails and slugs, cabbage white caterpillar on anything in the brassica family, aphids on soft new growth, and earwigs and slaters working through seedlings after dark. If seedlings are disappearing overnight and you can see nothing during the day, take a torch out at about 9pm and you will find out very quickly what is eating them.

A strong plant is a harder plant to eat

Most of what gets chewed badly is already under stress from something else, so the first half of pest management is not pest management at all.

• Feed the soil rather than the plant. Compost and aged manure dug through before planting give you steadier growth than a hit of liquid fertiliser does.
• Give them the spacing on the seed packet. Crowded plants stay damp, and damp foliage is where fungal problems and sap suckers both start.
• Move the crop families around. Planting brassicas in the same bed every year lets the pests that specialise in them build up in the soil.
• Water at the roots, early in the day. Wet leaves overnight is what fungal disease wants, and a plant watered at first light dries off as the day warms up.

Look often enough to catch it while it is small

A walk through the patch a couple of times a week, turning a few leaves over as you go, is worth more than any product on the shelf. You are looking underneath the leaves for eggs and for the first small colony of aphids, and along the stems for anything that has been chewed, and the whole thing takes about 5 minutes. Twenty aphids come off with your fingers. Two thousand do not.

The cheap fixes, in the order worth trying them

• Pick them off. Cabbage white caterpillars and snails come off by hand, and they go in a bucket rather than over the fence, because a snail carried to the other end of the yard will walk back.
• Put a barrier in the way. A copper or grit barrier around a seedling bed, or a simple slug trap sunk level with the soil, stops a lot of the night shift before it starts.
• Give them something they want more. Nasturtium planted at the edge of a bed pulls aphids and cabbage white off the crop you actually care about, and you pull the nasturtium out when it has done its job.
• Feed the predators. Alyssum, calendula and the small flowered daisies keep hoverflies and parasitic wasps in the garden, because the adults live on nectar even though the larvae are the ones eating your aphids.

Where companion planting earns its reputation, and where it does not

Trap cropping is real and it is the part of companion planting with the best evidence behind it. Flowers that feed beneficial insects are real too. The claim that a pot of basil by the back door repels flies and mosquitoes is a lot weaker than the internet suggests, and marigolds are often sold as a general pest repellent when the effect that has actually been measured is on root knot nematode, from growing a block of French marigold and digging the whole lot in as a green manure rather than dotting six plants through a bed.

None of that makes companion planting a waste of time. It means you plant the flowers because they feed the good bugs and because the patch looks better for them, and you do not rely on them as your only defence.

Home made sprays are not automatically the gentle option

A soap and water spray sounds harmless and it will burn foliage on a hot day or at the wrong concentration, and a garlic and chilli brew is inconsistent from one batch to the next because there is nothing controlling how strong it comes out. If you have got to the point of spraying, a registered product used at the rate on the label is the more predictable choice, and the label is also the only place that tells you the withholding period before you can pick and eat.

When you do spray, spray narrow

White oil and horticultural oils work by smothering, so they suit scale, aphids and mites, they need good coverage underneath the leaves, and they will damage foliage if you put them on in the heat of the day. Pyrethrum knocks down a lot in a hurry and it is honestly broad spectrum, which means it hits the ladybirds too, so it belongs at the end of the list rather than the start of it.

Spray late in the day once the bees have finished working, never on a plant that is in flower with bees on it, and only on the plant that has the problem. Half the value of integrated pest management is simply that you stop spraying the whole patch for something that is happening on one row.

Give it a season before you decide whether it is working, because the beneficial insects need somewhere to live before they can turn up and do anything. Everything I know about this I learned by getting it wrong first and then asking somebody who had already made that mistake, so come and have a yak with us in the shop if you are not sure what you are looking at.

Shop related products

• Brunnings White Oil RTU 1L. Ready to use, for scale, aphids and mites.
• Multicrop EcoPest Oil Insect Spray. An oil based spray for soft bodied insects.
• Multicrop Pyrethrum Long Life Insect Spray 1L. Fast knockdown, and broad, so keep it for last.
• D.T. Brown Alyssum, 750 seed pack. Nectar for hoverflies and parasitic wasps.
• D.T. Brown Nasturtium Jewel Mixed, 35 seed pack. The trap crop for aphids and cabbage white.

Did you know we also stock snail and slug pellets in two brands, a sunken slug trap, a 4 metre slug and snail barrier, slug gel and insect glue traps. None of those are on the website, so give us a ring on (08) 8536 4333 to check what is on the shelf.

The sprays, the seeds and the rest of it live in the garden centre, and the pest control range is the part of it you want for this.

Keep reading

• How to stop garden pests from ruining your vegetables without harsh chemicals
• How to attract ladybirds to the garden and keep them there

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