In the wild: Wild plants, shrubs, hedges and trees
In the garden: Ornamental trees and shrubs, including roses.
On Crops: Most vegetable fruit and ornamental plants.
Small, soft-bodied pear-shaped insects less than 3mm long are usually aphids. Depending on species and plant, aphids can be many different colours such as beige, green, yellow, red or almost black. They tend to congregate in groups on new growth or in leaf crevices. See also black bean aphids; rose aphids; mealy apple aphids and cabbage aphids. When aphids colonies become crowded or their host plants begin to die, winged aphids are produced that can then disperse to find new host plants. During the spring and summer months, most aphid species comprise only of females that produce live young. As winter approaches, winged males and females are usually produced which mate and then disperse to lay eggs on their overwintering hosts. Overwintering host plants are often different species to the summer host plants.
There are many symptoms of aphid damage, including decreased growth rates, mottled leaves, yellowing, stunted growth, curled leaves, browning, wilting, low yields and, eventually, death. Along with the loss of plant juices from direct feeding, aphids can spread diseases.
Check plants often for early outbreaks. Either squash the aphid clusters or remove, contain and destroy the parts of the plants where they are present. Encourage beneficial insects including ladybirds, hoverflies, and lacewings, which are important aphid predators.
In small outbreaks, a high-pressure spray from the garden hose can help remove aphids from plants. Where aphid problems persist, as a last resort organic pyrethrum-based pesticides are available from garden centres. These need to be applied following the instructions on the label.
Ladybirds and their larvae are very effective predators of aphids and should be welcomed into your garden. Other predators such as hoverfly larvae and lacewings also provide effective natural ways of controlling aphids. Parasitic wasps will help to control aphid infestations by injecting aphids with their eggs. The eggs hatch into maggots that eat the aphids from the inside out. Eventually the wasp maggots kill the aphids, turning them into ‘mummies’ before emerging from the mummified bodies as adult wasps. Ants will often farm aphids and collect the sugary honeydew that aphids produce. The ants protect aphids from predators and will move them to new plants to establish new aphid colonies.