Informational table showing disease name, symptoms, pathogen/cause, and management of Dahlia diseases. Disease Symptoms Pathogen/Cause Management Aster Yellows Leaf-like tissue forms where flower parts should be located. Flower-like parts remain green or light green. Phytoplasma Destroy infected plants. Control leafhoppers. Bacterial Stem Rot Blackened stems have a soft, wet, interior and a foul odor. Erwinia carotovora Promptly destroy infected plants Gray Mold In wet weather, masses of gray spores form on brown spots on buds, leaves or stems. Botrytis cinerea Maintain low relative humidity. Apply a fungicide to protect healthy plants. Powdery Mildew Dry, white, mealy, fungal growth occurs on the upper surface of leaves. Golovinomyces cichoracearum (formerly Erysiphe) Apply a fungicide when the fungus is first observed. Storage Rot Tubers decay into a soft smelly mass. Various fungi and bacteria. Avoid wounding the tubers. Let the tuber surfaces dry and remove soil before storing. Store tubers in a cool, dry location. Verticillium Wilt Single branches or the entire plant wilts and dies. Vascular tissue in affectes stems is black, dark brown, or greenish-brown. Verticillium Plant in pathogen-free potting mix. Virus Conspicuous rings and line patterns may be present or a mosaic of light and dark green may occur on leaves. Impatiens necrotic spot virus Discard infected plants. Do not save tubers from affected plants. Control thrips since they vector the virus.

Prepared by Gary W. Moorman, Professor of Plant Pathology