When a garden pest is worth spraying, and when it is not

Damage is not the same as a problem

The first thing worth saying is that a garden with no insect damage in it anywhere isn't a healthy garden, it's a sterile one, and chasing that is what turns gardening into a chore. Plants lose a bit of leaf. They grow more. A lettuce with three holes in the outside leaves is still a lettuce.

So before you buy anything, the question isn't whether something is eating your plants, because something always is. The question is whether it's eating enough to matter.

The test I use

Have a look at the plant and ask yourself which of these it is.

Cosmetic. Some holes in mature leaves, a bit of grazing, the plant is still putting on growth and it's still the colour it should be. Leave it. Come back in a week and see whether it got worse or whether something ate the thing that was eating it.

Slowing it down. New growth is being taken as fast as it appears, leaves are curling or going sticky, the plant is not getting any bigger. That's worth acting on, and often the cheapest action works.

Going to kill it. A seedling being cut off at the base overnight, a whole plant stripped, a trunk or stem being ringbarked. Act now, because there's no point being philosophical about a seedling that won't exist tomorrow.

Most of what people panic about is the first one, and most of what actually costs you a crop is the third one and it's usually snails.

Go and look at night

Half the mystery damage in a garden has no insect on it during the day, because the insect is under the pot or in the mulch until it gets dark. Take a torch out an hour after sunset and have a look at whatever's being chewed, and you'll generally find snails, slugs, earwigs or caterpillars in the act. That's ten minutes and it saves you buying the wrong thing.

The cheap things to try first

Pick them off. On a small patch this genuinely works for snails, caterpillars and the big obvious grubs, and it costs nothing. A bucket, a torch and five minutes a night for a week breaks the back of most snail problems.

Hose them off. Aphids on a soft tip will come off with a decent blast of water and a lot of them don't make it back up. Do it a few days running.

Cut the bit off. A single shoot covered in aphids or scale is easier to prune off and bin than it is to treat.

Put a barrier up. Fine netting over a brassica bed stops the white butterfly laying, which stops the caterpillars, which means there's nothing to spray later. A copper or grit barrier around a seedling bed slows snails down.

Feed and water it properly. A stressed plant gets hit harder and recovers slower, and a lot of aphid problems are a plant that got a big shot of nitrogen and put out a heap of soft growth.

When a spray is the right call

Reach for something when the damage is in the third category, when the cheap options haven't held after a week or so, or when it's a crop you'll actually lose. That's a reasonable line and it keeps a garden off a spray schedule.

When you do, pick the narrowest product for the job. A horticultural oil smothers scale, aphids and mites and doesn't do much to anything it doesn't land on. A dust or a spray made for tomato pests is aimed at that. A broad spectrum insecticide kills the predators as well as the pest, so it's the one that comes with a bill later.

Whatever you use, read the label for the withholding period on anything you're going to eat, spray late in the day when the bees have gone home, and do the affected plant rather than the whole garden.

Snails deserve their own paragraph

Around here snails are the ones that will actually cost you a bed of seedlings overnight, and they're worth getting on top of properly rather than tolerating. Pellets work, and the iron based ones are the ones to use where there are pets or chooks about. Put them out thinly in a scatter rather than in a pile, because a pile is exactly what a dog will find interesting.

Clear the hiding places at the same time. Snails sit under pots, along the edge of a raised bed and in long grass against a fence during the day, and going around lifting things up on a wet morning gets more of them than the pellets do.

Shop related products

• Brunnings White Oil RTU 1L. A horticultural oil for scale, aphids and mites.
• David Grays Tomato Dust 3-in-1. Aimed at the pests and diseases that go for tomatoes.
• Brunnings Bug and Fungus Kill RTU 1L. Ready to use, for when insects and a leaf disease turn up together.
• Multicrop Pyrethrum Long Life Insect Spray 1L. Broad spectrum, so it is the last option rather than the first.

Did you know we also stock snail and slug pellets, a slug barrier and a snail trap in the garden centre that aren't all listed online, so give us a ring on (08) 8536 4333 to check what's on the shelf.

The whole pest control shelf sits in the garden centre, and it's genuinely worth a two minute conversation in the shop before you buy, because the wrong product is money gone and the pest is still there.

More from the garden

• Which garden insects are worth keeping around
• How to get good bugs into the garden and keep pests down
• Companion planting, flowers to grow with your vegetables

I still go out with the torch and then stand there arguing with myself about whether a slater is doing any harm, so I'm not above the philosophical stage either.

Cheers,
Candeece

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