The woolly aphid (Subfamily: Eriosomatinae) is a sucking insect that lives on plant fluids and produces a filamentous waxy white covering which resembles cotton, fur or wool. The adults are winged and move to new locations where they can lay egg masses. The larvae often form large cottony masses on twigs, for protection from predators. At first it feels like that it is a fungus with time, they usually appear in the spring time on some plants, also can be seen at winters on tree stems usually on fruit trees and shrubs such as Apple, pear, Prunus, crab apple, cherries, apricot, pyracantha, cotoneaster and elm.
Woolly aphids feed by inserting their needle-like mouthparts into plant tissue to withdraw sap. They are able to feed on leaves, buds, bark, and even the roots of the tree. As a result of feeding on the sap, woolly aphids produce a sticky substance known as honeydew. Their action causes a callous-like lump or gall to grow, which provides better access to their reward. These remain after infestation has gone and affected branches do not usually regain their vigor so, if possible, they should be pruned out. If a plant is badly infested it may never recover properly and it might be better to replace it. The adults are about 2mm long and a pinkish-brown color, although they appear to be white with their waxy protection. They overwinter as young in crevices and cracks in the bark, emerging in the spring forming rapidly growing colonies on new shoots and at pruning cuts where the sap is more readily available. This causes weak growth of the plant and the leaves may fall due to the lack of sap to keep them functioning. Each adult can produce up to five live young per day and after a few generations winged adults develop to spread to new branches and nearby trees.
Treatments
Chemical –On edible apples, including crab apples, the trees can be sprayed thoroughly with deltamethrin (lambda-cyhalothrin or thiacloprid (ready to use formulation only). The minimum period that needs to be left between treatment and picking the fruit on apple trees for these pesticides is seven days for deltamethrin and lambda-cyhalothrin, or 14 days for thiacloprid. Avoid spraying during the flowering period. Use imidacloprid, pyrethroids or bifenthrin – spray as late in the day as possible to avoid Ladybirds and other friendly creatures.
Note: Follow directions and precautions given on packs, especially if treating fruit trees.
Organic
>Check tree shoots and bark regularly for signs of woolly aphid.
>Scrub areas within easy reach with a brush and a bucket of soapy water.
>Spray infested areas with a firm jet of water to help reduce aphid numbers.
>Spray with natural fatty acids such as an insecticidal soap.
>An acceptable organic spray is made from an extract of the Neem tree called Azadiractin.
>Few Herbals based (Ayurveda) insecticides also available which do not harm friendly insects. Please refer to www.himachalfruits.com/products
Biological Control
Natural enemies can be very important in the control of aphids, especially in gardens not sprayed with broad-spectrum pesticides (organophosphates, carbamates, and pyrethroids) that kill natural enemy species as well as pests. Usually, natural enemy populations do not appear in significant numbers until aphids begin to be numerous.
Among the most important natural enemies are various species of parasitic wasps that lay their eggs inside aphids. The skin of the parasitized aphid turns crusty and golden brown, a form called a mummy. The generation time of most parasites is quite short when the weather is warm, so once you begin to see mummies on your plants, the aphid population is likely to be reduced substantially within a week or two.
Many predators also feed on aphids. The most well-known are lady beetle, lacewing, and syrphid fly. Naturally occurring predators work best, especially in a small backyard situation.
Aphids are very susceptible to fungal diseases when it is humid. Whole colonies of aphids can be killed by these pathogens some fungi that infect and provide biological control of aphids, including Beauveria bassiana, Metarhizium anisopliae, Verticillium lecanii, and Neozygites fresenii, can provide good biological control of aphids.
Prevention
>Regularly check plants for signs of infestation and deal with them as soon as they appear.
>Encourage natural enemies like ladybirds, hoverflies and lacewings to become established in the garden by planting daisy-like flowers, yellow flowers and in particular, the poached egg plant Limnanthes douglasii.
>Avoid using broad spectrum insecticides which will kill beneficial insects as well as aphids.
>Encourage insect-eating birds such as, by hanging feeders in winter and nest boxes in spring.
>If planting new apple trees, use rootstocks which are resistant to apple woolly aphid.
>Use chemicals carefully, if possible, try to avoid, excessive use can harm trees and friendly insects and small birds.
Paint pruning wounds with a tree coating composition to help prevent infestations establishing.