Carrot-Aster Yellows

Aster-Yellows in Carrots
Aster-Yellows in Carrots

Aster Leafhopper (Whitney Cranshaw, Colorado State University)
Aster Leafhopper (Whitney Cranshaw, Colorado State University)

Casual Agents

Carrot-aster yellows is a disease caused by a bacterium-like organism called a phytoplasma. It can affect hundreds of species of broadleaf herbaceous plants, but primarily those in the aster family, as well as carrots. Aster-yellows is vectored by the aster leafhopper (Macrosteles quadrilineatus).


New leaves may turn yellow, become reduced in size, and appear deformed. Older leaves will turn a purple/ red color. The dormant buds on the crown may also develop a “witches’ broom” appearance.

Disease Cycle

The aster leafhoppers are active during summer, and when they feed on the phloem of infected host plants, they pick up the phytoplasma, and spread it to new hosts with their piercing-sucking mouthpart (stylet).


  • Removal. Remove infected plants as soon as they are detected.
  • Management should focus on aster leafhopper control.