|Aster yellows||Flowers develop green, elongate, or stunted petals and an excessive number of flower heads. The affected plants are usually stunted and yellowed.||Phytoplasma||Maintain good leafhopper control and eliminate nearby weeds that harbor aster yellows.|
|Bacterial leaf spot||Irregular brown blotches and spots develop on leaves.||Pseudomonas cichorii||Water in a manner that keeps leaf surfaces dry and water when the leaves will dry quickly. Remove infected plants. Apply a bactericide to protect plants.|
|Botrytis blight||Lower leaves die and become covered with white to gray, fluffy fungal growth that soon becomes a mass of gray spores.||Botrytis cinerea||Water in a manner that keeps leaf surfaces and flowers dry and water when the plants will dry quickly. Apply a fungicide to protect plants.|
|Crown rot||Plants wilt, brown, and die. White fungal growth webs at the base of the dying plant and become peppered with small, tan, round structures.||Sclerotium rolfsii||Remove infected plants. Mulch in a manner that does not hold moisture close to the stems.|
|Downy mildew||Black spots form on the upper leaf surface and white felt-like growth covers the underside of the leaf.||Plasmopara halstedii||Apply a fungicide to protect plants.|
|Fungal leaf spots||Purple to tan spots develop on leaves.||Cercospora, Septoria, Phyllosticta||Water in a manner that keeps leaf surfaces dry and water when the leaves will dry quickly. Apply a fungicide to protect plants.|
|Powdery mildew||White fuzzy growth develops on the upper side of the leaves.||Sphaerotheca macularis||Apply a fungicide to protect plants.|
|Root rot||Plants yellow, wilt, collapse, and die.||Phymatotrichopsis or Rhizoctonia||Apply a fungicide to protect plants.|
|Rust||Orange-yellow masses of spores form on the underside of leaves.||Coleosporium inconspicuum||Apply a fungicide to protect plants.|
|Scab||Leaves have a coating of gray to brown spores.||Cladosporium coreopsidis||Water in a manner that keeps leaf surfaces dry and water when the leaves will dry quickly. Apply a fungicide to protect plants.|
|Stem rot||Stems turn brown or tan and die as large portions of the plant collapse.||Alternaria sp., Rhizoctonia solani and Sclerotinia sclerotiorum||Remove infected plants. Cut plants back to the soil line in the fall. Mulch in a manner that does not hold moisture close to the stems. Apply a fungicide to protect plants.|
|Wilt||Plants wilt, turn brown and die.||Verticillium albo-atrum||Remove infected plants. This fungus survives in the soil for very long periods of time, even in the absence of susceptible plants. Do not plant susceptible varieties.|
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