The problem looks worse than it is. Miniscule mites secrete chemicals that cause blistering or blotches on the new leaves, which gradually turn blackish-brown. Although the mites breed prolifically, producing several generations over summer, the productivity of the tree isn’t usually affected.
Miniscule gall mites live in the foliage of pear trees. In spring, they secrete chemicals that cause blotches to appear on new foliage. These eventually turn black and the leaf dies, usually in late summer.
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Remove by hand any affected leaves and shoots.