Crossville Chronicle, Crossville, TN

Lifestyles

June 6, 2011

Plateau Gardening: Watch for aster yellows disease in your gardens

CROSSVILLE — When spring weather is especially rainy, some of the purple coneflowers (Echinacea purpurea) and/or yellow coneflowers (Echinacea paradoxa) in my yard develop Aster Yellows disease. 2011 has been that kind of year. Readers should check for signs of Aster Yellows in their landscapes. Remove plants infected by this disease and discard them.

The name might fool gardeners unfamiliar with this incurable disease into thinking flowering plants other than asters are immune, but that is not the case. Asters are only one of over three hundred plant species affected. Some susceptible plants are herbaceous ornamentals. They include coneflowers, chrysanthemums, coreopsis, cosmos, gladiolas, petunias and marigolds. Others (carrots, tomatoes, potatoes and onions) call the vegetable patch home. Among host plants that are common weeds are plantain and dandelions. 

I first saw an infected coneflower years ago while manning the Master Gardener desk at my county extension office. Multiple green flower heads on spindly stalks grew from the cone of the sample flower a resident brought in for diagnosis. Digital photos were sent to scientists at the University of Tennessee Plant Pathology lab via the Internet. These experts sent back a report indicating Aster Yellows disease caused the symptoms.

From the laboratory response I learned that this disease is spread by leaf hoppers. Leaf hoppers are tiny bugs that feed on plant juices. First, a leaf hopper ingests the disease causing agent (an organism known as phytoplasma) in infected plant juices. Afterwards each susceptible plant that bug feeds on becomes infected. While air temperatures are cool, signs of the disease do not show up. Only after the weather warms to 80 degrees or more and new growth develops, does the infection become obvious. By that time, the disease carrying leaf hopper is long gone.

Yellowing of veins on newly formed leaves, stunted, bushy growth with spindly stems and spindly flower stalks are early Aster Yellows symptoms. Flowers that form on diseased plants are often green and miss-shaped. Infected plants are affected in varied ways. On diseased carrots, leaves grow in tight bunches. Inner leaves are yellow and stunted. Outer leaves may turn either a rusty red or reddish purple. Infected carrot roots are not usable as food because they have a bitter taste, are deformed and have many hair-like surface roots.

There is no cure for this disease. The only way to stop the continued spread of Aster Yellows is to pull up and destroy infected plants. Removal of weeds that could become host plants from garden areas is also recommended. However, insecticides are not recommended as a control for leaf hoppers in home gardens.

I’ve been watching three purple coneflower plants in a bed out by my mailbox closely. I enjoy the beauty of healthy purple coneflowers and would hate to rip theses plants out prematurely but if they do have Aster Yellows disease, they continue to be a source of infection as long as they remain in my yard. The top leaves appear smaller and thinner than normal with pale yellow (instead of green) veins in the center of each leaf. Ugly, green, distorted flowers are typical of diseased purple coneflowers. Small flower buds formed weeks ago on these plants but they have not grown much and are still green instead of developing the big orange cone with drooping pink petals around it that is typical of this species. I fear the worst.

•••

Plateau Gardening is written by Master Gardeners for those tending home landscapes and gardens in Tennessee’s Upper Cumberland Region. UT Extension Cumberland County at P.O. Box 483, Crossville, TN 38557 (484-6743) has answers for horticulture questions, free publications and details on how to become a Master Gardener. Send email comments or yard and garden inquiries to Master Gardener Rae, mgardenerrae@frontiernet.net.

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