Anna Pavord's A to Z of pests and problems: I and J are for insects, insecticides and jealousy

From mealybugs to the dark side of garden visiting, Anna Pavord continues her A-Z of horticultural pests and problems...

Don't forget your natural friends, such as ladybirds, which as adults and larvae eat prodigious numbers of aphids (Getty Images)

Impatience

Impatience knocks the top off a juicy new plant in the greenhouse. Impatience trips you over a pot on the balcony and spills the contents on the floor. Impatience leads you to prune the wrong stem of a wisteria, so half the stuff you've been carefully growing up comes crashing down on your head. All those things have happened to me. And I've screamed with the frustration of knowing that it's nobody's fault but my own. Often these disasters happen because you are cramming a job into a time-frame that isn't big enough. Or you are in the wrong mood.

Impatience may also lead you to choose fast-growing plants for your garden. You need some (like Paris daisy, for pots) but fast-growing trees can all too soon present problems of their own. We live in an impatient age, used to quick results. Because people move around more than they used to, they only plant things that will be of immediate benefit. But instant gardening leads to layouts that, like instant food, are ultimately unsatisfying. In our gardens we can make a stand against trash. If the prevailing mood is now instant, disposable, our gardens can be places where the opposite things are going on. In our gardens, if in no other parts of our lives, we can dream a future that has no impatience in it.

Insects

To the gardener, there seem to be more baddies than goodies. There aren't, but the goodies are slower on the uptake and the gardener's patience is limited (see above). Aphids are the most common horrors, the green particularly enjoys roses, the black goes for dahlias and broad beans.

Whiteflies come in two varieties, indoor and outdoor. The indoor one is a menace in greenhouses. It is in artificial environments such as these, often without home-grown predators, that gardeners can introduce biological controls: the parasitic wasp (Encarsia formosa) that deals effectively with whitefly, the predatory mite (Phytoseiulus persimilis) that preys on red spider, the predatory beetle (Cryptolaemus montrouzieri) that hunts down mealybug. They work best in temperatures between 18-25C. Buy them mail order. Ladybird Plantcare (ladybirdplantcare.co.uk) charge £13.95 for a pack of 10 Cryptolaemus, £11.95 for a thousand Phytoseiulus.

But don't forget your natural friends, such as ladybirds, which as adults and larvae eat prodigious numbers of aphids. The larvae are the hungrier and can dispatch about 50 aphids each. They are slatey-blue with a few orange spots. Nettles will help ladybirds build up in spring in time for the big rose push. Ladybirds fatten up on nettle aphids.

You should also encourage ichneumon flies, by planting golden rod and fennel. Ichneumons are leggy, four-winged insects which prey on caterpillars. It is not a simple gobbling job. The female fly lays her egg inside a caterpillar and the larva eats its way out from the inside.

Centipedes are excellent predators. Slugs are their preferred diet but they will make do with other pests. Big black ground beetles (get an identification guide – there are 4,000 different British beetles) are also keen on slug breakfasts.

Insecticides

These should be used with extreme reluctance. In the natural cycle of events, pest build-up is followed by a similar build-up of predators, but there is a hiccup in the middle when gardeners are most likely to reach for the bottled final solution.

Unnatural imbalances are often caused by predators, such as cats, that we have artificially introduced into the natural chain. In cities, where there are more cats than could star in a million musicals, there are relatively few birds. This has an effect on the food chain.

Insecticides work in several ways. The simplest are those that kill by contact. You spray the bug. It drops down dead. Other insecticides leave a deposit on the leaf which is then eaten by the creature. Caterpillar killers work this way. Systemic insecticides are more devious. These are absorbed by the tissues of the host plant and get into the sap. The insects are killed by eating the plant that you have sprayed. Sap suckers such as greenfly and blackfly are usually tackled this way.

The least dangerous times to spray are early in the morning (say before 10am) or in the evening (after 6pm) when there are less beneficial insects on the wing and bees are less likely to be working flowers. Millions of bees, which do no harm to anyone, are killed each year by reckless spraying. The European Food Safety Authority has warned that insecticides containing the neonicotinoids imidacloprid and thiamethoxam may be a particular danger to bees. Spray when foliage is dry and when there is no wind. Use insecticides that are as specific as possible to the insects you want to get rid of.

J is for…

Jealousy

Jealousy is a regrettable trait but rife in the horticultural world. It takes gardeners in different ways. When you are a beginner, you are jealous of the speed and ease with which proper gardeners prune and sow and scuffle earth about with their feet to wonderful effect. This is blameless, however, compared with the far more devious jealousies that arise among seasoned gardeners. This is the dark side of garden visiting, now a national obsession to rival football.

"Well, of course she has a gardener," is one of the deflating phrases you hear as you admire an immaculate border. Or, "I've never really liked Salvia leucantha…". Then you watch as the despised salvias shift off the plant stall into the hands of their detractors faster than crockery at a Harrods' sale. Oscar Wilde had it sussed: "Anybody can sympathise with the sufferings of a friend, but it requires a very fine nature to sympathise with a friend's success".