>>>Just before this happens I see sticky syrup like drops on the leaves
recently I used a magnifying glass to look at the branches of the tree,
when the leaves were already falling off. There were many tiny dark brown
things stuck to the branches, the shape of a half pea but much smaller of
course. Closer towards the new growth , these things were light green and
almost transparent. I could not see legs or movement in this . <<<
Without actually looking at it, it sounds like scale (insects).
Effective treatment would be an oil spray like "Safer's Insecticidal Soap"
or a homemade spray concoction of 3T. cooking oil and 3T. ordinary dish soap
(Joy, Ivory Liquid) to a gallon of water.
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