Answer: The first thing that leaps to my mind is spittlebugs. You've probably seen them on herbaceous plant stems as little clumps of foam. The foam contains the nymph (juvenile stage) of a sap-sucking insect. They also inhabit trees. They seldom do much damage, but are known to spread plant diseases. I've researched other possibilities, and have come up empty handed. If you think it's something other than spittle bugs, have a local arborist or nursery expert help you track down the source - we can help you with a solution once the culprit has been identified. Good luck!
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