Aster Yellows

What is Aster Yellows?

Aster yellows is a chronic, systemic plant disease affecting over 300 species across 38 families. Its wide range of host plants and impactful symptoms make it a significant concern for both commercial growers and home gardeners.

Hosts include popular ornamental plants like aster, sunflower, marigold, vegetables such as carrot, lettuce, tomato, and various weeds.

Regions Impacted

The disease occurs in North America, Europe, and parts of Asia. Its spread correlates with the distribution of its insect vectors, primarily the aster leafhopper (Macrosteles quadrilineatus).

What are the Symptoms?

The most noticeable damage from aster yellows is the deformation and discoloration of flowers, which can make them unsellable or unsightly. In vegetables, the disease can render the produce inedible. Diagnosis in a lab, through DNA tests, can confirm the presence of the phytoplasma.

• Chlorosis: Leaves turn yellow or reddish-purple.
• Stunting: Infected plants often display stunted growth.
• Witches’ Broom: Excessive shoots may emerge from one location.
• Deformed Flowers: Flowers can become green and leaf-like.
• Vegetable Deformation: Carrots, for instance, might develop hairy, fibrous roots.

What Causes Aster Yellows?

Aster yellows is caused by a type of bacteria known as a phytoplasma. Phytoplasmas are specialized bacteria that lack cell walls and live inside plant phloem tissue. The specific phytoplasma responsible for aster yellows is Candidatus Phytoplasma asteris.

The disease is primarily transmitted by leafhoppers, especially the aster leafhopper (Macrosteles quadrilineatus). When these insects feed on the sap of an infected plant, they ingest the phytoplasma. Once inside the leafhopper, the phytoplasma multiplies and is then transmitted to other plants when the insect feeds again. The disease spreads as the leafhoppers move from plant to plant, sucking sap and introducing the bacteria into new hosts.

How to Control and Prevent Aster Yellows?

Controlling and preventing aster yellows can be challenging due to its wide host range and the mobility of its vector, the leafhopper. However, several strategies can help manage the disease:

Cultural Practices:

• Resistant Varieties: Select and plant varieties of susceptible plants that are resistant or tolerant to aster yellows.
• Garden Hygiene: Remove and destroy infected plants immediately to reduce sources of the phytoplasma.
• Plant Diversity: Incorporate a diverse range of plants in your garden. Some plants can repel leafhoppers or attract their natural enemies.

Monitoring & Mechanical Control:

• Yellow Sticky Traps: These can help monitor the presence of leafhoppers. While they may not control the population significantly, they can indicate when it’s time to take protective measures.
• Row Covers: Using floating row covers can protect susceptible plants, especially during the peak activity of leafhoppers.

Chemical Control:

• Insecticidal Soap and Neem Oil: These can deter leafhoppers but must be applied regularly.
• Chemical Insecticides: Products containing pyrethrin or other appropriate active ingredients can be effective against leafhoppers. However, use them judiciously to avoid harming beneficial insects and pollinators.

Biological Control:

• Encourage natural predators of leafhoppers, such as ladybugs, spiders, minute pirate bugs, and lacewings, by planting nectar-producing plants and avoiding unnecessary insecticide use.

Weed Control:

• Many weeds can host the aster yellows phytoplasma. Regularly weed your garden, focusing especially on removing perennial and annual weeds that are known hosts.

By combining multiple strategies, you can reduce the risk of aster yellows in your garden and landscape. Regularly monitoring plants for symptoms and taking action when the disease is detected can help manage its spread.