Gary W. Moorman, Professor of Plant Pathology
|ALTERNARIA LEAF SPOT||Large reddish brown or purple spots, at first round to oblong but becoming irregular in shape have gray or tan centers that may drop out leaving a hole. Severely affected leaves brown, dry, and become brittle.||Alternaria zinniae||Apply a fungicide. Whenever possible, water in a manner that keeps the leaves dry to inhibit this seedborn disease.|
|ASTER YELLOWS||Leaf-like tissue forms where flower parts should be located. Flower-like parts remain green or light green. Often flowers on only one side of the spoke show sympotms. Sepals may be very large or dwarfed.||Phytoplasma||Destroy infected plants. Control leafhoppers.|
|BACTERIAL LEAF SPOT||Spots reddish brown to dark brown, angular and with a prominent yellow halo form on leaves.||Xanthomonas campestris pv. zinniae||No sprays are effective. Whenever possible, water in a manner that keeps the leaves dry to inhibit this seedborn disease.|
|POWDERY MILDEW||White fungal growth forms on the upper surface of leaves and may form on flower petals.||Golovinomyces cichoracearum (formerly Erysiphe)||Apply a fungicide to protect plants.|
Alternaria leaf spot. Bacterial leaf spot (those with yellow halo)
Alternaria leaf spot (purple spot, no halo).
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