You could take a sample for them to look at. Possible Insects Potato leafhopper causes upward curling of the leaf tips. Large areas of brown circled with a yellow band result. The light green wedge-shaped insect feeds on the underside of the leaves. Use Diazinon dust, methoxychlor, rotenone or Sevin for control.
Mites cause the leaves to be spotted and dried out.
Spray rotenone to control the problem. Some diseases Rust can infect leaves, stems or other green parts. Brown pinhead size spots develop on the underside of leaves. The upper leaf surface will show larger bright yellow or orange spots with reddish centers. If the spots run together they cause the death of large leaf areas.