|Alternaria leaf spot||Small dark brown to black leaf spots become oblong and develop lighter-colored centers as they enlarge. Spots on young plants are often along the midrib.||Alternaria||Water in a manner that keeps moisture off the leaves and stems. Apply a fungicide to protect plants.|
|Aster yellows||Flowers remain green. Leaf-like structures form in place of some flower parts and tight clusters of such flowers may form. In the spring, foliage may be bright yellow.||Aster yellows phytoplasma spread by leafhoppers||Remove infected plants. Remove weeds in the area and other aster-related plants that have similar symptoms.|
|Bacterial leaf spot||Dark brown to black spots form on leaves and are angular in shape because they are limited by large leaf veins. The spots often have a yellow halo||Pseudomonas cichorii||Water in a manner that keeps moisture off the leaves and stems. Apply bactericide to protect healthy plants|
|Botrytis leaf spot and stem rot||Brown spotting on leaves is sometimes accompanied by a stem rot.||Botrytis cinerea||Water in a manner that keeps moisture off the leaves and stems.Apply a fungicide to protect plants.|
|Cercospora leaf spot||Brown spots from on the leaves. Tiny black dots are seen within the spots.||Cercospora tabacina||Water in a manner that keeps moisture off the leaves and stems. Apply a fungicide to protect plants.|
|Foliar nematode||Purplish, angular spots form between veins. The spots become tan with age.||Aphelenchoides||Most other perennials are also susceptible to foliar nematode. Examine all surrounding plants for similar symptoms. Remove infected plants. Water in a manner that keeps moisture off the leaves and stems.|
|Leaf mottle||Light and dark green blotches develop on leaves. Sometimes there dark green ring spots present or line patterns and etches formed by dead tissue.||Impatiens necrotic spot virus (INSV), cucumber mosaic virus (CMV), and others||Remove infected plants. Control thrips (that move INSV) and aphids (that move CMV).|
|Sclerotinia and Sclerotium crown rot||Plants with dark spots on lower stems and dark roots wilt and die. White fungus with dark granule-like (Sclerotinia) or tan balls (Sclerotium) structures form on the surface of the dead areas.||Sclerotinia sclerotiorum and Sclerotium rolfsii||Remove infected plants.|
|Septoria leaf spot||Purplish-brown spots develop on the leaves, often completely covering older leaves.||Septoria lepachydis||Water in a manner that keeps moisture off the leaves and stems.|
|White smut||Yellow spots form on the leaves and become brown with age.||Entyloma compositarum||Several plants in the aster family are susceptible and should be examined for symptoms. Apply a fungicide to protect plants.|
Prepared by Gary W. Moorman, Plant Pathology Professor
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