Aster yellows

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Quick facts

Aster yellows is a plant disease that can infect many common vegetables, annual flowering plants, perennial flowering plants and weeds.
Infected plants have yellow, stunted growth, and small malformed flowers.
Aster leafhoppers can carry the aster yellows pathogen. Plants become infected when fed upon by these leafhoppers.
Once infected with aster yellows, a plant will never recover.
Plants infected with aster yellows should be removed from the garden and composted.

Symptoms of aster yellows

A petunia plant with discolored leaves and stunted, discolored flowers — Infected petunia did not develop to normal size or color

Leaves are discolored pale green to yellow or white.
In some plants, red to purple discoloration of leaves occurs.
Leaves may be small and stunted.
Flowers are small, malformed and often remain green or fail to develop the proper color.
Plants infected early in the growing season may remain small and stunted.
Many thin, weak stems grow close together forming a witches' broom.
Tap roots of carrots are thin, small, covered in many root hairs, and often taste bitter.

How to manage aster yellows

Once a plant is infected with aster yellows, there is no way to cure it.
Completely remove infected plants from the garden.
Compost infected plant material. Aster yellows will not survive once the plant is dead.
Remove perennial weeds from the garden. If infected with aster yellows, the bacteria will survive in weeds from one season to the next.
Protect plants from aster leafhoppers with light colored or reflective mulches that disorient the insects and can reduce feeding on plants.
In the vegetable garden, floating row covers can be used to prevent leafhoppers from feeding on plants.
Pesticides are not effective in reducing aster yellows in the home garden.

Understanding aster yellows

Aster yellows is caused by a phytoplasma, a very small specialized type of bacteria that can live only within the veins of a plant or within a sap sucking insect called the aster leafhopper.

How does aster yellows spread?

Discolored and malformed purple coneflowers — Purple cone flowers infected with aster yellows

When aster leafhoppers feed on a plant infected with aster yellows, they suck up some of the aster yellows phytoplasma along with the plant sap.

The phytoplasma moves through the insect's gut into the salivary glands. This process takes two weeks.
After that period, whenever the leafhopper feeds, aster yellows phytoplasmas are released into the plant, starting a new infection.
The leafhopper will spread aster yellows every time it feeds for the rest of its life.

green insect with yellow markings and wings on a leaf — Adult aster leafhopper

How does aster yellows affect the plant?

The aster yellows phytoplasma moves through the plant, infecting every part, from the roots through the flowers.
The disease affects the plant's growth, development and ability to store nutrients.

How does aster yellows survive Minnesota’s winter?

Aster yellows does not survive in plant debris of infected plants or in soil.
It can survive in the crown and roots of infected perennial plants, including perennial weeds.
The aster yellows phytoplasma can live within aster leafhoppers, but these insects do not survive through the winter in Minnesota.
Most aster leafhoppers spend the winters in southern states feeding on grain crops and other plants.
Aster leafhoppers arrive in Minnesota early in the growing season. Weather systems carry the insects north early in the growing season.
The aster leafhopper population that arrives in Minnesota each year varies in size and in the percent of the population carrying the phytoplasma.
In years where leafhopper populations are high, many cases of aster yellows are reported in landscape flowers and vegetable gardens.
In years where leafhopper populations are low, only a few cases of aster yellows occur.

Michelle Grabowski, Extension educator

Reviewed in 2018