Aster Yellows

Aster Yellows Aster yellows is a severe disease of many flowers and vegetables. It is caused by a bacterial-like organism and is carried by the aster leafhopper. The leafhoppers annually migrate to Colorado from overwintering areas along the Gulf of Mexico. Once insects feed and acquire the disease organism, they remain infective for life.

Aster yellows is a chronic, systemic disease that affects over 300 species in 38 families of broad-leaf, herbaceous plants. Members of the aster family (Asteraceae), such as asters, marigolds, Coreopsis and purple coneflower are commonly affected by this disease. Vegetable crops such as carrots and potatoes are also susceptible. Aster yellows occurs throughout North America.

Life Cycle:The bacterium survives on residues, in soil and on seed. It is spread by splashing rain, wind and plant-to-plant contact (1). The bacteria can exist for some time in a symptomless phase on leaves of wheat. It is when they invade wounds or natural openings in leaves or heads, where they multiple and kill tissues, that damage results (6). Entrance into the plant is through stomata and wounds. The bacterium lives intercellularly, especially in creases that harbor free water (3). When wheat matures, the bacterium is harvested with the seed. When planted, the bacterium returns to the soil in crop residues.Seed formed in diseased heads will be contaminated with the bacterium

Damage:Aster yellows is a common plant disease that affects a wide range of flowers, vegetables and weeds. Susceptible flowers include asters, cockscomb, chrysanthemum, coreopsis, cosmos, echinacea (purple coneflower), dianthus, glads, marigolds and petunias. Entire plantings of marigolds can be destroyed. Susceptible vegetables include carrots, potatoes, onions and tomatoes. Dandelions and plantain are also susceptible and can serve as sources of the disease in home gardens.vein clearing in leaf (24523 bytes)The first symptom of the disease is vein clearing, the loss of chlorophyll or green pigment in the leafaster yellows on echinecia2.jpg (43268 bytes) veins.

This is followed by yellowing of newly formed leaves, sporadic bushy growth, erect growing habit, and stunting. Stems and flower stalks may be numerous and spindly. Flowers often remain green and become distorted. Seeds and fruit do not develop. Specific symptoms vary with the kind of plant.The leaves of infected carrots grow in tight bunches. The inner leaves are yellow and stunted, while outer leaves turn rusty red to reddish purple. The roots are bitter, stunted and deformed, with tiny hair-like roots growing all over the main root.

Control:Where possible, eradicate all susceptible overwintering hosts in and around crop and ornamental plantings. Destroy infected plants as soon as they appear.Do not plant a susceptible crop next to a yellows-infected crop.Spray susceptible plants with an insecticide suggested by Illinois Extension Entomologists to control the aster leafhopper. Refer to Illinois Extension Circular C1373, Midwest Vegetable Production Guide for Commercial Growers (revised annually) available from ITCS, P345, 1917 S. Wright St.Ext., Champaign, IL 61820 or your nearest Extension office.

Spray before removing infected crop plants.Weed hosts growing near crops in fields, fence rows, ditch banks, and roadways should be destroyed or should be sprayed early and repeatedly with insecticide to help prevent the spread of disease from these reservoirs. Fast-growing crops such as lettuce or valuable crops such as asters and chrysanthemums should be grown under a cloth screen (22 threads to the inch) or wire screening (18 threads to the inch). In small plantings, placing aluminum foil strips as a mulch between the rows is thought to increase control because leafhoppers are disoriented by bright light from below. In small plantings, removing the first infected plants may slow the spread of the disease.There are no resistant or immune crop varieties available.

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