The following question was sent to the P&PDL diagnosticians here at Purdue University:
Question: I have a white foamy substance on several of my backyard plants. It seems like it may be spreading to others. We just moved to our home, so I do not know what kinds of plants these are. At first I thought it was part of one plant, but now it is on it's neighbor and they are different kinds of plants. Does this have to do with some sort of insect?
Answer: It sounds like the problem you are describing is with an insect called a spittlebug. There are two kinds of spittlebugs, pine (see photo) and meadow. Meadow spittlebugs commonly attack clover, flowers, and arborviae whereas pine spittlebugs attack spruces, firs, scots, austrian, and white pines.
These insects are small as nymphs and protect themselves by secreting a frothy, white mass which is actually their secretion from sucking sap and other nutrients from the plant. This spittle protects them from the sun and other insects. While the spittle is unappealing to the sight, the spittlebug does little damage if in small quantities. Severe infestation can cause leaf, branch, or even plant death.
If necessary, insecticidal soap or horticultural oil will control these if coverage is thorough. A broad-spectrum insecticide can also be used. When using pesticides, read and follow label directions.
-Nathan E. Saxe (June 9, 1998)