Gardeners' hearts may sink at the sight of fluffy white patches on their plants, but getting rid of the infestation is possible once the correct pest is identified. Mealy bugs and woolly aphids are different pests that cause similar effects. Mealy bugs produce a layer of rough white wax and usually infest houseplants and greenhouse plants. Woolly aphids create a similar layer on apple, crabapple, pyracantha and cotoneaster trees and shrubs. Controlling each pest requires different approaches.
Controlling mealy bugs
Remove mealy bugs on sight and cut off infected foliage. Wash secateurs in hot, soapy water, dry thoroughly and wipe with oil after use to avoid infecting other plants. Remove dead leaves and prunings from greenhouses.
Introduce the ladybird biological control Cryptolaemus montrouzieri to greenhouses between May and September, when temperatures are warm enough for the insect to survive. Don't remove insects, which may be ladybird larvae, or use insecticides when using this control.
Spray infected plants with an insecticide. Organic insecticides containing fatty acids work on contact with mealy bugs, and need frequent application. They're safe to use on edible plants. Systemic insecticides are absorbed by plants and make them poisonous to mealybugs. Systemic insecticides are suitable for ornamental plants.
Scrub woolly aphid infestations within reach with a stiff brush and soapy water in spring and early summer. Spray jets of water from a garden hose at infestations out of reach. Encourage woolly aphid predators, such as hoverflies and lacewings, into the garden by growing flowers that attract them, such as poached egg plant (Limnanthes douglasii), and providing undisturbed corners of the garden as overwintering sites.
Spray edible plants such as apples or crabapples with an insecticidal soap spray, or use a chemical insecticide for woolly aphids. Wait at least seven days before harvesting apples from trees after using a chemical insecticide, or according to manufacturer's instructions.
Spray ornamental plants with an insecticide for woolly aphids on ornamental plants. Don't spray during flowering.
When buying indoor plants, check them closely for signs of infestation, then quarantine them in a separate room away from other plants for a month. Discard infected plants.
The parasitic wasp Leptomastix dactylopii is another biological control for mealybug.
Check regularly for signs of pest infestation and deal with them immediately to help prevent infection spreading.
Wear gloves when using chemical insecticides.