Aster yellows is a chronic, systemic plant disease caused by several bacteria called phytoplasma.

However, in agricultural settings such as carrot fields, some applications of chemical insecticides have proven to minimize the infection rate by killing the vector.

The largest family affected is the Asteraceae, and ornamental plants commonly infected are asters, marigolds, coreopsis, sunflowers,[4] and purple coneflower.

[2] Regarding vegetable crops, onion, lettuce, celery, and carrot are affected, with the latter suffering the greatest losses.

[6] Characteristic symptoms specific to the carrot include initial vein clearing and chlorosis, followed by the production of many adventitious shoots, with the tops looking like a witches’-broom.

The carrot roots are predisposed to soft rots in the field and storage and taste unpleasant to the consumer.

[citation needed] Phytoplasmas are small (0.5-1 μm in diameter) prokaryotes that reproduce by division or budding in the phloem sieve cells of the host plants and the bodies of their leafhopper vectors.

Some examples of weed host plants are thistle, wild carrot, dandelion, field daisy, black-eyed Susan, and wide-leafed plantain.

[7] The vector leafhopper feeds on the phloem of aster yellows-infected plants by inserting its straw-like mouthpart, a stylet, into the cell and extracting it.

[7] Hardly any conditions directly affect the development of aster yellows, but a few indirect factors strongly influence the rate of transmission by the leafhopper.

[citation needed] Transcontinental migration begins in the spring when the prevailing winds and jet streams help carry the leafhoppers from their overwintering sites in the South to the Midwest.

This means that hot and dry conditions are less conducive to the spread of aster yellows than times of abundant rainfall.

[citation needed] On an agricultural level, speaking specifically about carrots, some methods can be used to manage the leafhopper populations in an attempt to control AYP spread.

[2] The resulting number can determine when to apply insecticides based on how susceptible the crop or cultivar is to leafhopper feeding.