Common pests Aphids. which come in several colours, feed on almost all cultivated plants, weakening them and spreading virus diseases.Greenfly, blackfly – they are both aphids, as are other small, round-bodied insects which can be white, pink, red, yellow or even multicoloured. Between them, the black and green aphids are probably the commonest pests in gardens.
The insects, which are mostly but not always wingless, feed on sap, distorting young leaves and shoots and depositing honeydew which encourages moulds. Even more serious, aphids transmit virus diseases, and while there are ways and sprays for dealing with insects and fungal moulds, there are no cures for virus diseases.
Getting rid of aphids
Spray with a contact insecticide as soon as you notice any of the insects on your plants. Some gardeners also swear by traditional remedies, such as spraying with soapy water, water with washing-up liquid added, or with an infusion of cigarette ends or boiled rhubarb leaves. But most scientists argue that a jet of plain water would be just as effective.
Where aphids are well protected from the effects of contact sprays by curled leaves or waxy coverings, choose a more persistent systemic insecticide. These insecticides penetrate the leaves to enter the sap stream, killing any insect that attempts to feed on the plant.
The pests attack in spring and early summer outdoors, but can be a nuisance at any time under glass. At the end of summer, adult aphids lay their eggs on trees and bushes, where they hatch out in the following spring. So next year’s problems can be reduced by tackling the eggs, before they hatch, with a tar-oil spray. These sprays should be used only in winter and only on bare-branched plants, because the chemicals will burn any green foliage they touch. Don’t I spray on very frosty days, though, the water in the spray can freeze, leaving the oil unable to penetrate the cracks in the bark where the eggs are usually laid.
Ants and aphids
The ants are not the real problem, as they do not directly harm the plants. They are attracted by your real enemy – aphids such as blackfly or greenfly. The aphids excrete a sticky, sweet substance called honeydew on which the ants feed. The ants will even protect the aphids from predators such as ladybirds so that they have a constant source of food, and will also carry greenflies from one plant to another.
The only other trouble that ants cause the gardener is when they loosen the soil round roots as they hollow out a nest amid their shelter – and the plants wilt for lack of support. Anthills in a lawn are unsightly, too.
The most effective way to get rid of the ants directly is with an insecticide dust or spray on their nests. Much better, though, to spray the foliage of your plants to kill off the pests that started the problem in the first place . The ants will then move elsewhere to look for food.