The foliage of your pear tree can be an early warning system, if something is wrong with the tree. It's useful to be able to identify each specific problem, so that the correct course of action can be taken.
A common pest of pears, leaf midges are tiny black grubs that cause the edges of the leaves to roll upward. Young foliage is more likely to be attacked than older leaves. The affected leaves may turn red and drop. Control is difficult, as the grubs are protected from spray by the curl. Any affected leaves should be picked off and burnt.
Greenfly and Aphid
Several species of greenfly can attack pears. Some greenfly can cause yellowing and curling of leaves. The rosy leaf-curling aphid can cause a distortion and reddening of foliage. They attack all plant growth, but tender foliage is most vulnerable.
Leaf Blister Mite
These microscopic mites leave foliage spotted with yellow or red blisters, and they can cause the leaves to curl. Affected leaves may fall early and fruit may be blistered. Any infected leaves should be removed and destroyed.