Answer: Sounds like an insect population. The foam can be from spittlebugs or there may be a colony of mealybugs on the leaves; the black spots may be sooty mold which develops when insects are feeding on the leaves. Start by hosing off the trees with a strong stream of water from the hose. Direct the spray on both the upper and undersides of the leaves to dislodge the pests. Check periodically and if you see signs of more insect pests, spray them off again. Eventually you will eliminate the pests. Good luck with your trees!
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