Advice
RHS Help & Advice
Winter washes on fruit trees and bushes
Tar oil winter washes
are no longer available for controlling the overwintering stages of pests
on deciduous fruit trees and bushes. These include scale insects
and the eggs of apple sucker, winter moth and most aphids.
An alternative product, based on plant oils, is now available and can be used to control overwintering eggs of aphids and other insects.
Woolly aphid on apple is less well controlled because it overwinters
as immature nymphs concealed under loose flakes of bark.
Crops that can be treated
Dormant apples, pears, plums, cherries, peaches, currants, gooseberries, grape vines and summer-fruiting raspberries during the winter.
Before you spray
Examine the shoots and branches, particularly in crevices around buds, to assess whether pest eggs are numerous or not. Aphid eggs are 1mm long, shiny black and oval; apple sucker eggs are similar but pale yellow. A x10 hand lens will be useful for detecting these eggs.
Timing
Winter washes may scorch leaves and other soft growth so use only on fully dormant deciduous plants. If the buds have begun to break it is too late for this type of treatment. To achieve best results, trees or bushes should be sprayed thoroughly on a mild day when the bark is dry. Avoid windy days when spray may drift and harm neighbouring plants. Before you spray cover nearby plants that are in leaf with plastic sheeting.
Products
Growing Success Winter Tree Wash, which is based on plant oils, is the only product now available for use as a winter wash. It has little persistence on plants and thorough application is necessary for good control.
Note
As winter washes are non-specific, they may harm overwintering beneficial insects and mites, but remember that spring and summer pesticides currently approved for use on fruit trees and bushes are also non-selective.