White Woolly Aphids Control

Cultural Controls

• Regularly spraying infested trees or shrubs with a forceful spray of water can wash honeydew off of the plant and dislodge and kill some of the woolly aphids. Using too much nitrogen fertilizer, or using fast-release formulas, can encourage a flush of tender new growth that's particularly attractive to aphids. Selectively prune off stems and water sprouts that are heavily infested with woolly aphids to reduce pest numbers.

Preserving Natural Aphid Enemies

• Woolly aphids have several natural enemies that help to control these pests, including parasitic wasps, lacewings, lady beetles and hover flies. Avoid using broad-spectrum, persistent pesticides to try to control woolly aphids or other pests nearby, as these products will have a lasting negative impact on the populations of beneficial insects. Ants may also harvest the honeydew produced by the aphids and protect the aphids from their natural enemies. In this case, you need to control the ants with bait stations or sticks placed in their trails or by wrapping the trunk or stem of infested plants with a band of sticky material that will trap ants climbing the tree.

Chemical Sprays

• Woolly aphids are more difficult to control with regular contact pesticides than other aphids because of their protective waxy covering. Thorough sprays of a horticultural oil can partially control of these pests. Spraying during the dormant season can help control overwintering eggs, though it will not address aphids that fly in from your neighbor's garden. This type of spray is most helpful when you are attempting to control other pests, like scale insects, that are also overwintering on the tree. Follow manufacturer recommendations for product dilution, which varies depending on the product's formula and the type of plant. Often, 5 tablespoons per 1 gallon of water is appropriate. Use a garden sprayer and thoroughly cover the entire surface of the plant's trunk or stem and branches, focusing on twig ends and branch undersides. Only apply horticultural oils when temperatures are between 40 and 90 degrees Fahrenheit and do not apply within 30 days of a sulfur application. Do not apply horticultural oil to plants that are under drought stress. Check the product's label, as instructions vary by brand.

Soil Drenches

• Drenching the soil around infested or vulnerable trees or shrubs with a systemic insecticide, like imidacloprid, can control woolly aphid feeding for the entire growing season. The plant absorbs the chemicals, which are then translocated to aphid feeding sites within about two to four weeks. Measure the insecticide into a bucket, dilute with water according to manufacturer recommendations and pour this solution over the soil near the base of the tree or shrub. Dilution rates and quantities depend on the size of the plant. For example, a 1.47 percent imidacloprid pesticide might need 1 ounce of product per 1 inch of trunk diameter. For shrubs, the quantity may be 3 ounces per 1 foot of shrub height. You dilute the pesticide in 1 gallon of water or, for very large trees, 2 gallons. Apply the soil drench in late winter or spring just as new leaves are emerging. Read the label on the product you buy because instructions vary.