Aphids and Dying Shrubs

• Aphids can make your shrubs look terrible by removing essential fluids. Larry Mayer/Creatas/Getty Images

  Aphids are common plant pests. Almost every plant is subject to damage from at least one species of aphid. Aphid infestations draw fluids out of shrubs and other plants, making them look as if they are dying. Aphids are slow to kill and can be controlled before they destroy shrubs.

Description

• Yellow, brown, red or black, these small, long-legged, pear-shaped insects have distinguishing tube-like appendages called cornicles projecting from their rear body parts. They have slender, pointy mouthparts that pierce stems, leaves and other parts of plants to suck out plant fluids. Aphids generally do not have wings, but wings can appear on some individuals when food is scarce and they need to disperse. Aphids usually feed in dense groups and cannot easily be detached from the plant.

Damage

• An aphid infestation causes the leaves of shrubs to turn yellow and become distorted. Shoots of new growth can be stunted. Some aphid species produce quantities of a sticky substance called honeydew. Honeydew turns black when it becomes infected with a sooty mold fungus. Some aphid species inject a toxin into the shrub, causing even more distortion of new growth. Some aphids carry viruses they transmit to shrubs. The viruses, like the aphids themselves, cause mottling, yellowing or coloring of the leaves of the shrub and stunt its growth.

Finding Aphids

• Examine shrubs for aphid infestation by inspecting the underside of leaves. If your shrubs are large, clip leaves from several areas. Do a thorough inspection. Look for aphid predators, such as ladybugs, lacewings and syrphid fly larvae, which could be indicators of aphid infestation.

Biological Control

• There are several biological means of getting rid of aphids. Aphid predators usually do not turn up naturally until your shrubs are infested, but you can add natural predators if you suspect aphids. Among biological-control agents are ladybugs and lacewings. Also very effective are several species of parasitic wasps that lay their eggs inside the aphids. The evidence that the wasp treatment is working is that you will see the crusty, light brown skins of dead aphids on your shrubs. Predators that eat aphids include lady beetle adults and larvae, lacewing larvae and syrphid fly larvae. In humid weather, aphids often succumb to fungal diseases, but this is more a matter of chance than of any action on your part.

Garden Practices

• Ants feed on honeydew and protect aphids from their natural enemies, thus putting your shrubs at risk. Use ant stakes, dusts, granules or baits on the ground to control the ants. Use a fertilizer with the minimum amount of nitrogen your shrubs need, as nitrogen supports aphid reproduction. Sometimes you can remove aphids by spraying your shrubs with a strong jet of water. Make sure the shrub is sturdy enough that it will not be damaged.