Skip to content
growing.guide
Menu

Aster yellows

Aster yellows is caused by a phytoplasma, a bacterium without a cell wall, carried by the aster leafhopper. Carrots grow bunches of yellow shoots and hairy, bitter roots; lettuce centres turn yellow and twisted.

Bacterial diseases
A carrot with a bunch of thin yellow shoots from aster yellows
A carrot with a bunch of thin yellow shoots from aster yellows

What it looks like

Odd growth rather than spots.

  • A witches'-broom of thin yellow shoots from the carrot crown.
    Bunched shoots A witches'-broom of thin yellow shoots from the carrot crown.
  • Older carrot leaves turn red or purple.
    Reddened leaves Older carrot leaves turn red or purple.
  • Roots grow many fine hairs and taste bitter.
    Hairy roots Roots grow many fine hairs and taste bitter.
  • Lettuce hearts yellow and twist.
    Twisted lettuce Lettuce hearts yellow and twist.

How to confirm it

Look at crowns and roots.

  1. Bunched yellow shoots

    Distinctive clusters at the crown.

  2. Hairy, bitter roots

    Confirms it on carrots.

  3. Leafhoppers

    Small hopping insects around the crop.

What to do

Remove and protect.

  1. Remove plants

    Pull and bin affected plants.

  2. Cover crops

    Use fine row covers to keep leafhoppers off.

  3. Control weeds

    Many weeds carry the disease.

  4. Plant resistant types

    Some lettuce varieties are more tolerant.

Prevent it next time

  • Cover susceptible crops in summer.
  • Keep weeds down around beds.
  • Remove infected ornamentals in the daisy family.

What not to do

Do not leave infected plants in the bed; they are a source for leafhoppers.

In the growing guides

Where the guides mention it, with plant-specific advice.

Sources

  1. Aster yellows, Utah State University Extension