Downy mildew causes seedlings to wilt and die. On older plants the foliage is mottled light yellow. No chemical control is listed.
Several leaf spots may be found but are not serious. Remove and destroy infected leaves. No chemical control is listed.
Powdery mildew may cause a white powdery growth on the leaves in late summer. Applications of benomyl will control the disease.
White smut causes light spots on the leaves. Destroy plant residues in the fall and get rid of infected plants as they are noticed. No chemical controls are listed.
Verticillium wilt may kill rudbeckia. No chemical control is listed.