Aster yellows infects various perennials

Univ. of Ga. plant pathologist Jean Williams-Woodward discussed diseases of herbaceous perennials at this year’s Perennial Plan Association conference in Atlanta. Univ. of Md. entomologist Stanton Gill reports that Williams-Woodward talked about aster yellows, which is caused by a phytoplasma bacteria-like organism. The disease infects a variety of perennials, including Echinacea, Veronica, Aster, Coreopsis, Dahlia, Dianthus, Gaillardia, Phlox and Rudbeckia.
Leafhoppers are normally the vector of the disease in the South, but it can be transmitted by grafting of root systems. Once a plant is infected in the landscape, surrounding plants are often infected in the same season or in the next season.
The phytoplasma grows in the phloem of infected plants causing a disruption of plant hormone flow that results in growth distortions. Infected plants turn yellow, bronze and stunted with sterile flowers forming. Gill said infected Echinacea have tiny, distorted green leaves and short stems.
There is no control once plants are infected and discarding infected plants is the best action. Gill said soil drenches of imidacloprid early in the season may help to keep the leafhopper population down. Applications of dinotefuron can be tried to keep the leafhopper population under control and reduce the chance of a leafhopper infestation.