Pests like aphids and spider mites are known to be dangerous to fruit trees, such as apple trees. The pests use the trees as a place to reproduce and will infest the them quickly, eating away from the inside and bringing various contagions into the plant along with them. Although insecticides and pesticides are effective at removing such problems, winter wash is a known alternative for today's green gardeners.
There are a variety of pests that threaten common apple trees, including codling moth larvae, fruit slugworms, aphids and spider mites that may burrow into the tree and fruit to lay eggs. The result is infestation with the pest's larvae, which tend to be more resistant toward countermeasures than adults. The burrowing also allows plant contagions into the tree, infecting from the inside, often eventually causing death.
Winter wash is a blend of natural chemicals, oils and products used by gardeners for pest treatment. These products are typically made for use with fruit trees such as apple, plum pear, cherry and peach. Fruit-bearing bushes such as blackberry, raspberry and gooseberry also may benefit from similar products.
Winter washes are generally made from natural oils and products that have a natural physical reaction with pests, keeping them away from the tree and making them unable to reproduce. A major component of many winter washes is tar oil--Mortegg emulsion--which is a powerful repellent to many common insect pests. Since winter wash is not an insecticide, and mostly non-toxic, it does not have the same ecological threats as other chemical-based pest treatments that, when not absorbed by plants or soil, become pollutants that often drift off toward the nearest water supply.
Diluting liquid winter wash is often done by gardeners before use to prevent waste. The diluted mixture is then sprayed with a coarse sprayer on the outer surface of the tree's trunk and leaves to repel insect pests. The wash repels current infestations of pests and prevents others.
A study at the Northern Ireland Horticulture and Plant Breeding Station, done to test the effectiveness of winter washes versus their chemical-based counterparts, found there was no difference between the immediate results of the two pest control methods. But unlike many pesticides, some winter washes don't prevent a resurgence of infestation and must be reapplied multiple times during a season.