|Aster yellows||Leaf-like structures form where flower parts should be located. Plants may branch abnormally heavily (witches’ broom), leaves may be yellow and plants may be stunted.||Phytoplasma ( bacterial-like organism)||Remove and destroy infected plants. Control leafhoppers early in the season with insecticides in order to suppress spread of the pathogen from weeks to your plants.|
|Bacterial leaf spots||Angular, brown to purplish spots primarily on lower leaves may kill the entire leaf.||Pseudomonas and Xanthomonas||At the end of the season, remove all above ground plant parts. Avoid using sprinkler irrigation.|
|Downy mildew||Dark, blotchy areas on upper leaf surfaces and grayish white fuzzy growth on leaf undersides.||Plasmopara halstedii||Provide good air circulation around the plants.|
|Fungal leaf spots||Brown spots on lower leaves spread upward during wet weather or when sprinkler irrigation is used.||Cercospora tabacina, Cercospora rudbeckiae, Corynespora cassiicola, Phyllosticta rudbeckiae, Ramularia rudbeckiae, Alternaria, Cylindrocladium Colletotrichum.||Start with healthy plants and do not purchase any with spots on leaves. Remove infected leaves and provide good air circulation around the plants. Avoid using sprinkler irrigation.|
|Powdery mildew||White fungal growth on leaves causes them to yellow, die and fall prematurely.||Phyllactinia and Golovinomyces||Avoid using high nitrogen fertilizer because succulent growth is very susceptible to this disease.|
|Rusts||Dusty, rusty red spores form in blister-like spots on leaves and stems.||Uromyces perigynius, U. rudbeckiae, Puccinia dioicae, Aecidum batesii.||Some Carex species (sedges) act as alternate hosts of Uromyces and Puccinia. If grown close to Rudbeckia, the disease may be severe.|
|Septoria leaf spot||Dark brown to purplish spots 1/8 to ¼ inch in diameter may be rounded or angular in shape starting on the lower leaves and spreading upward when the weather is wet or when sprinkler irrigation is used.||Septoria rudbeckiae||Start with healthy plants and do not purchase ones with spots on the leaves. Do not use sprinkler irrigation.|
|Stem rot||Lower leaves yellow, wilt, and die. The entire plant may die. White, cottony fungal growth forms at the soil line; Small, white to reddish brown balls or black, long (mouse dropping-sized) structures form on the white growth.||Sclerotium and Sclerotinia||Remove and destroy infected plants and even remove and replace the topsoil immediately around the plant. Do not attempt to compost the dead plant material.|
|Verticillum wilt||Leaves yellow, brown, and wilt.||Verticillium||Diseased plants should be removed and destroyed. Verticillium survives in soil for many years in soil.|
|Viruses||Light and dark green mosaic coloration forms on the leaves. Leaves may be distorted and the plants stunted.||Rudbeckia mosaic (RuMV), Potato yellow dwarf (PYDV), Tomato spotted wilt (TSWV), Tobacco streak (ToSV), and Bidens mottle (BiMV)||Obtain a diagnosis from a plant disease clinic to confirm the identity of the virus present. Some are spread only by insects while others are spread on your hands and tools. Remove and destroy infected plants.|
Prepared by Gary W. Moorman, Professor of Plant Pathology
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Issued in furtherance of Cooperative Extension work, Acts of Congress, May 8 and June 30, 1914, in cooperation with the U. S. Department of Penn State College of Agricultural Sciences research and extension programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.
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