Aster Yellows

Species


Aster Yellows Disease

Related species

Symptoms of aster yellows are often mistaken for damage from herbicide exposure.

Host/site


Aster yellows disease (AYD) affects over 300 species of plants, including ornamentals such as aster, coneflower, zinnia, marigold, chrysanthemum, petunia, and snapdragon. Edibles affected include lettuce, carrot, tomato, potato, onion and celery. Weeds include plantain, dandelion, and other broad-leafed weeds. Grasses and grains also are can also be affected.

A major symptom of aster yellows is chlorosis, yellowing of the leaves while the veins remain green. Growth slows down and leaves may be smaller, more narrow than usual and foliage may be curled. Flowers may be deformed and exhibit bizarre tufts of deformed leaves inside the flower or in place of the flower. Floral parts that are normally brightly colored may remain green, and petals and sepals may become puckered and distorted. However, it is important to remember that symptoms of AYD often differ depending upon what species is infected.

Identification


Indicators
  • Typical symptoms of aster yellows include veins that turn pale, yellowing of new leaves, abnormally bushy growth, deformed flowers, and stunting.
    Infected plants often have a stiff, upright appearance, with branches joining the stem at narrow angles. The appearance of this disease varies with the host plant.
  • Infected onion plants will have leaves that are small, twisted and yellow.
  • Symptoms are more pronounced in hot weather, and in cool weather a plant can be infected without showing any symptoms.
Life cycle
  • Aster yellows is primarily transmitted by leafhoppers. When a leafhopper feeds on a plant infected with aster yellows it becomes "infected" with the phytoplasma and remains infected throughout its life. The phytoplasma cells multiply and cause infection of feeding insects salivary glands within one to three weeks. When the infected insects feed on healthy plants, they inject the phytoplasma cells into the plant phloem. Susceptible plants will be symptomatic in 10 to 40 days.
  • The spread of aster yellows is worse in cool, wet summers.

Natural Enemies


There are no natural enemies of this disease. Visit the leafhoppers fact sheet for information on their natural enemies.

Monitoring


Monitor plants for symptoms regularly throughout the growing season.

Action Thresholds


The disease is incurable so early diagnosis is key in preventing it from spreading to other parts of the garden.

Cultural and Physical Controls


  • Although AYD is an incurable disease there are a few actions home gardeners can take to prevent further spreading.
  • Remove diseased plants: Early diagnosis and prompt removal of infected plants may help reduce the spread of the disease. Although the disease itself is not fatal to the plant, its presence makes it impossible for a plant to fulfill its intended role in the garden.
  • Plant less susceptible plant species: As long as infected leafhoppers are around, they can infect plants. A practical way to avoid having problems with this disease is to grow plants that are not as susceptible to aster yellows. Verbena, salvia, nicotiana, geranium, cockscomb, and impatiens are among the least susceptible plants.
  • Control leafhoppers: Vegetable growers may protect susceptible crops by using floating row covers to keep leafhoppers and other insects away from the plants. Some growers put strips of aluminum foil between rows because bright reflections of sunlight can confuse the leafhoppers.
  • Control weeds: Remove weeds in your lawn, garden, and surrounding areas, especially plantain and dandelion that can harbor the disease.

Biological Controls


No known biological controls are available for aster yellows.

Chemical Controls


There are no known chemical controls.

References


Engelbrecht, Christine. Horticulture and Home Pest News. Publication. Iowa State University, 13 Sept. 2006. Web. 1 July 2010. <http://www.ipm.iastate.edu/ipm/hortnews/node/166>.

Hudelson, Brian. University of Wisonsin Garden Facts; Aster Yellows. Fact Sheet. University of Wisconsin, 27 Dec. 2002. Web. 1 July 2010. <wihort.uwex.edu/gardenfacts/X1080.pdf>.

O'Mara, Judith, Robert Baurenfeid, Alan Stevens, Karen L.B. Gast, and Susan Stevens. Commercial Specialty Cut Flower Production ASTER YELLOWS. Publication. Kansas State University, Oct. 1993. Web. 1 July 2010. <www.ksre.ksu.edu/library/hort2/mf1086.pdf>.

William T. Kemper Center. "MBG Integrated Pest Management." Missouri Botanical Garden. MIssouri Botanical Garden, 2010. Web. 02 July 2010. <http://www.mobot.org/gardeninghelp/PlantFinder/IPM.asp?code=138&group=67&level=s>.

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