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Aster yellows

Aster yellows is a severe disease that affects many flowers and vegetables. It is caused by a bacterial-like organism and is carried by the aster leafhopper. Leafhoppers migrate annually to Colorado from overwintering areas along the Gulf of Mexico. Once these insects acquire the disease organism, they carry and spread it for their entire life.

Aster yellows affects 300 species of plants including aster, marigold, zinnia, petunia, lettuce, carrots, beets and onions. Though symptoms vary, plants usually show yellowed, bronzed and twisted new shoots or flower growth. The most severe symptoms are seen in late July and August and don't let up until frost.

Controlling aster yellows is difficult. As long as leafhoppers abound, the disease can be carried to plants. The most practical remedy for repeated disease occurrences over several seasons may be to grow less susceptible flowers. These include nicotiana, geraniums, salvia, cockscomb, impatiens, portulaca and verbena.