Potato leafhopper injury results in severely stunted plants that may not bloom. Early symptoms are pale-colored foliage that curls and browns along the leaf edges. Of the two, the tarnished plant bug is the more common. Malathion or rotenone will control them, but frequent applications may be necessary if insects are abundant. Treat only if the insects and their damage are present.
Mites are tiny, and difficult to see with the unaided eye.
Although seldom a problem, mites can be difficult to control once established. Upon hatching in spring, the small worms migrate to dahlias and bore into the lower stem. Keep the areas near the garden free of weeds and grasses, and remove or thoroughly cover plant material remaining in the garden in the fall. In severe problem areas it may be necessary to apply an insecticide to the lower stem and around the plant base weekly during June. Thrips are found in open flowers but also may damage opening buds if the insects are abundant.