The leafhoppers annually migrate to Colorado from overwintering areas along the Gulf of Mexico. Once insects feed and acquire the disease organism, they remain infective for life. Aster yellows affect some 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 shoot or flower growth. The most severe symptoms are seen in late July and August and don't let up until frost.
Control is difficult.
As long as leafhoppers abound, the disease can be carried to plants. And leafhoppers may move into gardens from many areas. 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. Photograph of Aster Yellows on Chrysanthemums courtesy of University of Delaware.