- Melon

Melon Melon

Aster Yellows Phytoplasma

Bacteria

Phytoplasma asteris


In a Nutshell

  • Clearing of the leaf veins that extends to the rest of the leaf blade.
  • Deformation and greening of flowers, development of leaf-like flower petals and formation of sterile flowers.
  • Overall, plants have a reduced root system and a stunted appearance.

Symptoms

The range of characteristic symptoms varies slightly depending on strain of phytoplasma in question, the age of the plant during the infection, the plant species and environmental factors such as temperature and humidity. The symptoms can easily be mistaken for herbicide damage and usually start with the clearing of the veins. Later on, the chlorosis extends to the rest of the leaf blade, until i engulfs it entirely. In some crops, the foliage may be reddening instead. Other symptoms include the deformation and greening of flowers, the development of leaf-like flower petals and the formation of sterile flowers. Overall, plants have a reduced root system and a stunted appearance.

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Hosts

Trigger

The symptoms are caused by an obligate bacterial parasite of plant vascular tissues called phytoplasma asteris. The plant-to-plant transmission is mostly through insect vectors, mainly leafhoppers. Conditions that favor the movement and feeding of these insects in the field also enhance the spread of the phytoplasma. For example, wind, rainfall or temperatures below 15°C can temporarily halt their migration and delay the time of infection. Weather conditions of the region also greatly influence leafhopper feeding patterns. If conditions are hot, plants are less nutrient-rich and become less attractive to the leafhoppers. Seasons with abundant rainfall allow the plants to have much more lush growth and become more attractive. The leafhoppers then feed all summer until they migrate back to their overwintering sites in the fall.

Organic Control

Apply bioinsecticides containing parasitic fungi species such as Metarhizium anisopliae, Beauveria bassiana, Paecilomyces fumosoroseus and Verticillium lecanii to control acute infestation. Use parasitic insect species such as Anagrus atomus as a biological control method for the leafhoppers. Beneficial insects such as ladybugs and lacewing are also voracious predators of both the egg and larval stage of these insects. Insecticidal soaps also work.

Chemical Control

Always consider an integrated apporach with preventive measures together with biological treatments if available. Formulations based on lambda-cyhalothrin, dimethoate, and indoxacarb show a relatively high efficacy towards leafhoppers and can help to limit the spread of the disease in the field.

Preventive Measures

  • Regularly monitor the fields for symptoms of leafhopper infestation and of the disease.
  • Infected plants should be removed to eliminate the source of the phytoplasma and minimize spread.
  • Use yellow sticky traps that are very attractive to green leafhoppers.
  • Try to promote a good environment for beneficial insects such as ladybugs, parasitic wasps and lacewing.
  • Since leafhoppers can overwinter in weeds and perennial ornamentals, such as thistle, dandelion, and carrots, avoid these plants in the field.

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