Long, strapy leaflets that have curled-up leaf margins are the sure sign of a leaf roll mite infestation. The adjacent photo shows two pecan leaves; The leaf on the right is normal while the one on the left has been attacked by leaf roll mite. These eriophyoid mites are extremely small and visible only under high magification. Leaf roll mites attack only expanding leaves. They feed along leaflet edges causing the leaflet to roll upwards and inwards to form a protective area for the development of mite offspring.
A closer look at a mite infested leaflet (at right) reveals that the leaflet margins have become thickened and almost gall like. Leaf roll mite damage is often confused with herbicide injury but only a mite infestation will cause rolled-up and thickened leaflet margins.
Leaf roll mite is a minor pest that rarely requires treatment. You usally need to look long and hard to find infested trees and those trees seem to grow out of the damage.