|Aster yellows||Leaves are yellowed and flowers do not appear normal or of good quality.||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 spot||Areas between veins turn dark brown and collapse. The entire plant may be killed||Pseudomonas||Remove and destroy infected plants. Do not use sprinkler irrigation.|
|White smut||At first light green spots, some with tan centers, form on the leaves and white spores form on the spots. The leaf spots become dark brown.||Entyloma spp.||Remove and destroy spotted leaves. Apply a fungicide to protect plants.|
|Septoria leaf spot||Tan spots containing tiny dark brown to black dot-like fungal fruiting structures form on the leaves.||Septoria||Do not use sprinkler irrigation.|
|Powdery mildew||White fungal growth develops on the surface of leaves.||Golovinomyces and Sphaerotheca||Apply a fungicide to protect plants.|
|Root and stem rots||Lower stems turn tan to dark brown. Sometimes white webs of fungal growth can be seen.||Pythium, Sclerotinia, Thielaviopsis, Rhizoctonia||Avoid overwatering and do not mound mulch against the plant.|
|Viruses||Leaves may be distorted or have patches of light and dark green coloration||Impatiens necrotic spot, tomato spotted wilt, or and cucumber mosaic virus||Remove and destroy infected plants. Control thrips (vector of impatiens necrotic spot and tomato spotted wilt) and aphids (vectors of cucumber mosaic).|
Septoria leaf spot
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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