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- 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
- 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.
- 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.
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.
Reviewed in 2018