Aster Yellows: How to Identify, Treat and Prevent?

HomeProblemsDiseaseAster Yellows: How to Identify, Treat and Prevent?

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Aster yellows is a chronic, systemic plant disease that affects over 300 species of plants, including many vegetables, grains, ornamentals, and weeds. It is caused by a bacterium-like organism called phytoplasma, which lives inside the plant tissues and disrupts their normal growth and development. Aster yellows can cause severe losses in crop quality and yield, as well as aesthetic damage to ornamental plants.

Aster yellows is a difficult disease to manage because it has a wide host range, a persistent vector (the aster leafhopper), and no known cure. Once a plant is infected with aster yellows, it will never recover and will remain a source of inoculum for further spread of the disease. Therefore, early identification and removal of infected plants are crucial to limit the impact of aster yellows on your crops or flowers. Additionally, you should implement cultural, biological, and chemical methods to reduce the population and movement of the aster leafhopper, which is the main way that aster yellows are transmitted from plant to plant.

What is Aster Yellows Disease?

Aster yellows is a disease caused by Candidatus Phytoplasma asteris, a type of bacterium without cell walls that can only survive inside plant cells. The phytoplasma invades the phloem (the vascular tissue that transports sugars and other nutrients) of the plant and interferes with its normal functions. The phytoplasma also produces proteins that alter the expression of plant genes, resulting in abnormal growth and development. Aster yellows affect plants in 38 families of broad-leaf herbaceous plants, primarily in the aster family (Asteraceae), as well as important cereal crops such as wheat and barley.

What are Aster Yellow Symptoms?

The symptoms of aster yellows vary depending on the plant species, the phytoplasma strain, the timing of infection, the temperature, and the age and size of the plant. However, some common symptoms include:

  • Stunted growth and reduced root system.
  • Yellowing or reddening of foliage.
  • Distorted leaves, stems, and flowers.
  • Virescence (greening of flowers) or phyllody (development of leaf-like flower petals).
  • Sterility or reduced seed production.
  • Formation of bulb-like structures in flowers or fruits.

Some examples of aster yellows symptoms in different plants are:

  • Carrot: vein clearing and chlorosis of leaves, the proliferation of shoots (witches’-broom), twisted and broken petioles, bronze or red foliage.
  • Lettuce: yellowing and curling of leaves, stunted heads, malformed flowers.
  • Onion: yellowing and twisting of leaves, stunted bulbs, virescent flowers.
  • Spinach: yellowing and curling of leaves, reduced leaf size.
  • Canola: yellowing and wilting of leaves, stunted plants, malformed pods.
  • Wheat & Barley: yellowing and stunting of leaves, reduced tillering, sterile heads.
  • Aster, Sunflower & Marigold: yellowing and stunting of leaves, virescent or phyllodes flowers.
  • Coreopsis: yellowing and stunting of leaves, virescent, or phyllodes flowers.

How is Aster Yellows Transmitted?

As mentioned earlier, the primary culprit is the aster leafhopper. These tiny insects feed on plant sap and, if carrying the phytoplasma, unknowingly transfer it to healthy plants during their meal. Additionally, the phytoplasma can be accidentally transmitted through pruning tools, grafting, or even during weed removal if infected plant material comes into contact with healthy tissues.

How To Treat Aster Yellows?

The unfortunate truth is that there’s no cure for aster yellows once a plant is infected. Infected plants should be removed and destroyed as soon as possible to prevent further spread of the disease. Do not compost or use infected plants as mulch, as the phytoplasma can survive in plant debris for several months. If you suspect that your plants have aster yellows, you can send samples to a diagnostic laboratory for confirmation.

What Causes Aster Yellows?

Aster yellows are caused by phytoplasma, a type of bacterium without cell walls that can only live inside plant cells. The phytoplasma invades the phloem of the plant and interferes with its normal functions. The phytoplasma also produces proteins that alter the expression of plant genes, resulting in abnormal growth and development.

How to Prevent Aster Yellows?

The best way to prevent aster yellows is to avoid introducing the disease into your garden or farm. You should only buy or exchange plants or plant materials from reputable sources that are certified free of aster yellows and other diseases. Inspect your plants regularly for signs of aster yellows and remove any infected plants promptly. To reduce the risk of local spread by the aster leafhopper, you should implement the following measures:

  • Use resistant or tolerant varieties of plants when available.
  • Plant early or late in the season to avoid peak leafhopper activity.
  • Use row covers or netting to exclude leafhoppers from young plants.
  • Maintain good weed control to eliminate alternative hosts for leafhoppers and phytoplasmas.
  • Use yellow sticky traps to monitor leafhopper populations and movement.
  • Apply insecticides to control leafhoppers when necessary, following label instructions and safety precautions.

FAQs

Can I eat vegetables infected with aster yellows?

It is not recommended to eat vegetables infected with aster yellows, as they may have reduced nutritional value, bitter taste, or toxic compounds. Additionally, eating infected vegetables may increase the risk of spreading the disease to other plants.

Can I save seeds from plants infected with aster yellows?

No, you should not save seeds from plants infected with aster yellows, as they may be sterile, malformed, or contaminated with the phytoplasma.

Can I use insect repellents or barriers to protect my plants from aster yellows?

Insect repellents or barriers may help to deter or exclude leafhoppers from your plants, but they are not 100% effective. You should still monitor your plants for signs of aster yellows and remove any infected plants promptly.

Can I use natural remedies or homeopathic treatments to cure my plants of aster yellows?

No, there is no scientific evidence that natural remedies or homeopathic treatments can cure plants of aster yellows. Infected plants should be removed and destroyed as soon as possible to prevent further spread of the disease.

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