Woolly aphids are small soft bodied insects, reddish to brown in colour, up to 2 mm long and covered in masses of white wool-like material. They are found on stems, branches and roots, and do not infest leaves. When squashed they leave a red residue. If Aphid infestation is heavy it may cause leaves to yellow and/or become distorted, or cause necrotic spots on leaves and/or stunted shoots. Aphids secrete a sticky, sugary substance called honeydew which encourages the growth of sooty mold on the plant.
Plant Part: Stems and branches, Fruit, Roots
Season: Spring - Summer
Symptoms: Twigs and branches - Aphids colonize around wounds on scaffold limbs, on twigs and water sprouts. Colonies can also cause galls on twigs and the bark to crack.
Fruit - Honeydew may drip on the fruit causing russet spots and blackened lenticels.
Roots - Aphid feeding causes galls or swollen enlargements on roots, and heavy infestations can reduce growth or cause death of the tree. The root colonies also cause re-infestations each year.
Control: If aphid population is limited to just a few leaves or shoots, the infestation can be pruned out to provide control. Sturdy plants can be sprayed with a strong jet of water to knock aphids from leaves. Insecticides are generally only required to treat aphids if the infestation is high - plants generally tolerate low and medium level infestation. Insecticidal soaps or horticultural oils are usually the best method of control. Always check the labels of the products for specific usage guidelines prior to use.
Prevention: Biological Control - Several predators (lady beetles, syrphid flies, green lacewings, earwigs) play an important role in woolly apple aphid control. Encourage predatory insects by reducing broad spectrum insecticide use on your trees.
Paint large pruning cuts with commercial pruning paint to discourage aphid populations.