Aster yellows

Aster yellows is a chronic, systemic plant disease caused by a group of bacteria called phytoplasmas, collectively known as the aster yellows phytoplasma, which is spread from plant to plant by the aster leafhopper. The disease affects more than three hundred plant species across thirty eight families, with its heaviest impact on members of the daisy family such as asters, marigolds, coreopsis and purple coneflower, as well as vegetable crops including carrots, lettuce, celery and onions. Infected plants show stunting, yellowing of the leaves, deformed flowers, reduced root systems and sterility, and in carrots the disease produces a witches broom of twisted leaves and misshapen roots. Carrot yields can fall by an average of twenty five percent and occasionally as much as eighty percent, and just fifteen percent infected carrots in a processed batch can make the whole batch unmarketable because of poor flavor. There is no cure, so management relies on removing infected plants and controlling the leafhopper vector with insecticides. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/