If nuts are damaged during the period in which they are enlarging, the damaged tissue turns brown and necrotic and the outside will often become sunken. The internal lesions often develop a white netted appearance in the shell tissue, with no deep pitting. After shell hardening in June, leaffooted bugs may cause a second type of damage called kernel necrosis, which is not obvious on the shell. Externally all that is evident is a brown pinpoint mark. With kernel necrosis, the nutmeat is darkened, often develops a sunken or distorted area, and may have an off-flavor.
Leaffooted plant bugs typically damage entire clusters.
However, if they overwinter in or near pistachio, they may be found earlier, usually feeding on nut clusters. Sample for them using a beating tray. Hold the tray under nut clusters while striking the limb sharply three times with a lightweight club. The insects will drop onto the tray and can be easily examined. Look for small, black nuts in clusters or on the ground in late April to early May for the first indication of bug presence in the orchard.