Of the many diseases that attack perennials, aster yellows, botrytis blight, powdery mildew and rust are the most serious.

Aster yellows

(mycoplasma) causes the yellowing of leaf tips and flowers, also stunting of the plant and abnormal growth. Leafhopper insects carry this disease from plant to plant. Asters, mums, statice and some others can get aster yellows.

The only cure is to remove the infected plants and to control leafhoppers.

Botrytis blight (fungus) is a gray mold that attacks leaves, stems and flowers. Most flower petals are susceptible, especially peony flowers in wet weather and shasta daisy in late summer during times of heavy dew.

Leaf blotch can be caused by other fungi as well. Brown spots are a common problem on peony, iris and mum.

Root rots (fungus, bacteria) can be serious problems for perennials in moist soil. The best solution is to improve soil drainage, especially over winter, or move the plant to a more suitable location.

Powdery mildew

(fungus) covers leaves with a whitish substance. Avoid overcrowding and planting in wet or shady locations. It often occurs on monarda, phlox and delphinium.

Rust (fungus) causes reddish brown spotting on leaves, young stems and flower parts. Rust is common on hollyhocks.

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