Yoshie Tachiki of Los Angeles wrote to the SoCal Garden Clinic to ask:
We have a Fuji apple tree that has a white, cotton-like substance on the limbs. Is it a fungus? What can we use to get rid of it?
For an answer, we turned to Yvonne Savio, manager of the UC Cooperative Extension's Common Ground Garden Program for Los Angeles County. She oversees the training of master gardeners. Savio said:
The cottony fuzz is from woolly apple aphids. Wash it off with a stiff spray from the hose, making sure to get into the crevasses to dislodge the bug. Do this early in the morning, so the sun can dry off the bark by sundown.
Questions for our garden clinic — plant health emergencies, plant selection conundrums, design quandaries — can be sent to firstname.lastname@example.org. Please put “SoCal Garden Clinic” in the subject line, and include a photo if you'd like. Because of the volume of mail we receive, we cannot respond to all questions.