Tennessee Dahlia Society

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.	Phytoplasm	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 fludioxonil, iprodione, or mancozeb to protect plants.
Powdery Mildew	Dry, white, mealy, fungal growth occurs on the upper surface of leaves.	Erysiphe cichoracearum	Apply Ampelomyces, myclobutanil, ziram, mancozeb, thiophanate methyl + mancozeb, fenarimol, triadimefon, or triforine when the fungus is first observed.
Storage Rot	Tubers decay into a soft smelly mass.	Various fungi and bacteria	Avoid wounding the tubers when digging them for storage. Let the tuber surfaces dry after digging and removing soil and before storing. Store tubers in a cool, dry location.
Verticillium Wilt	Single branches or the entire plant wilts and dies. Vascular tissue in affected stems is black, dark brown, or greenish-brown.	Verticillium	Discard infected tubers. Fumigate infested soil before planting.
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.