Use sprays of Orthene when the caterpillars are first seen. Waiting until the insects are full grown before spraying will not be beneficial. Leaf spots caused by several fungi can attack catalpa. A symptom of all is brown spots on the leaves. Leaf spots are rarely serious so no chemical control is suggested.
Powdery mildew causes a white powdery coating on the leaves.
When severe, the leaves yellow and fall off. Catalpa is susceptible to verticillium wilt . Branches die and eventually the entire tree may die. A symptom of verticillium wilt is discoloration of the sapwood but it is hard to find. Fertilize with a high nitrogen fertilizer.