Coneflowers (Echinacea sp) are popular perennial flowering plants that come in a variety of cheerful colors. Reaching heights of 3 to 4 feet tall and growing in clumps, they present a striking accent to the mid-summer garden. The blooming period generally lasts for two months, so there is always an explosion of color. Although coneflowers are quite easy to grow, they are subject to certain diseases. Unfortunately, for some, there is no cure. Keeping the garden clean of debris and plant detritus may help prevent disease.
Aster yellows, transferred to the plant by the aster leafhopper, can cause the death of coneflower plants. It is caused by a type of bacteria known as a phytoplasma, which is a parasite that feeds off the plant's phloem (the tissue that carries nutrients throughout the plant). Symptoms include the loss of pigment in older leaves and yellowing of new leaves. Stems may get anemic and the flowers distorted. There is no cure for aster yellows and scientists at the University of Minnesota say that infected plants should be removed from the garden and destroyed. They also suggest the use of oat straw mulch as a method of discouraging the leafhopper. There is also a mite that causes some of the same symptoms as aster yellows, so take a sample of the plant to the country cooperative extension office for a definitive diagnosis.
This coneflower disease is generally caused by one of two bacteria: Pseudomanas or Xanthomonas. Pseudomanas causes reddish brown to black spots on the coneflower's leaves while Xanthomonas causes small brown spots with yellow halos. There is no chemical or biological control for bacteria in the garden. Experts with the University of Illinois Extension say that good hygienic garden practices are the only controls against bacterial infections. They suggest that the gardener avoid working on wet coneflower plants, as it is too easy to bruise them and cause an opening in which bacteria might enter. Clearing away dead and decaying plant matter from the soil also helps.
Also known as botrytis, gray mold will turn the coneflower's leaves brown and they may appear to be dead. If there is adequate moisture, the leaves may appear moldy and look gray and fuzzy. Gray mold is caused by a fungus that feeds on all parts of the plant, eventually killing it. Good garden hygiene goes a long way in preventing botrytis, as it needs standing moisture to infect. Fix soil drainage problems and remove all detritus from the area. Management of the disease includes the use of fungicides. Your county cooperative extension agent can suggest the appropriate product for use in your area.