Winter wash is an application that kills the egg status of many important pests such as various types of aphids, mites, weevils and moths. It also helps control the spores of fungal diseases.
Winter tree wash used to be simply Bordeaux mixture, based on copper sulphate and slaked lime. This was first used on vines initially to discourage pilferers. Its fungicidal and bactericidal properties were discovered by chance. For many years, it was used on fruit trees. The copper in the mixture combated both fungal diseases and the pests as listed above. Bordeaux mixture was ideal as a winter fungicide because it adhered to trees even in rainy weather. It could even be made by farmers themselves, using 10 pounds of copper sulphate, 10 pounds of dry hydrated lime, and 100 gallons of water (or 3.5 tablespoons of copper sulphate, 10 tablespoons of dry hydrated lime, and 1 gallon of water).
Today, in the UK, Bordeaux mixture is illegal. A replacement is made by VITAX, which is now the only firm in the UK manufacturing a winter fruit tree wash. The Vitax replacement is legal and effective. It is based on natural plant and fish oils, and it works by physical means: in other words, it can be used on edible crops, because it is non-toxic and is suitable for organic growing. It should be applied in dry conditions during the trees’ dormant period.
When winter washing fruit trees, spray as a fine mist, covering all areas of trunk and the main branches, and taking care to reach all the hidden clefts in the bark and crooks between branches and trunk – in other words, places where insect eggs are liable to be.