Several fungi cause cankers leading to dieback. Fertilize to keep plants healthy and prune out infected parts.
Fusarium wilt infects roots, causing the leaves to droop and wilt.
A light infection causes only gradual dwarfing or yellowing and premature red leaf coloration. There is no chemical control. Leaf spot caused by Pezizella oenotherae causes gray spots with purplish margins that merge, giving the leaves a scorched appearance. No chemical control is listed. Various genera of powdery mildew forms a white coating on the leaves.