Aster yellows has been a conspicuous problem in home gardens this year particularly on purple coneflowers. This disease is vectored by the aster leafhopper, Macrosteles quadrilineatus. The following aster leafhopper biology is modified from a fact sheet written by Bill Hutchison. To view the original publication, go to Bill's VegEdge website.
The major source of aster leafhoppers in Minnesota is the spring migration of adults from the southern United States. Migration of aster leafhopper occurs via transport on northern jet streams. Several weeks after their arrival, a small number of aster leafhoppers hatch from overwintering eggs found in winter wheat or other grass species. Five nymphal stages are completed in about 2 weeks.
Important vegetables that serve as hosts include lettuce, celery, carrots, endice, and parsnip. During early to mid summer, as winter grasses senesce, newly emerged adult aster leafhoppers move to these crops, as well as more succulent spring grain, weed hosts, and susceptible vegetable, ornamental and field crops. Common weed hosts for aster yellows include: thistle, fleabane, wild lettuce, sow thistle, chicory, wild carrot, galinsoga, dandelion, plantain, cinquefoil and others. Susceptible flowers include aster, chrysanthemum, cockscomb, coreopsis, cosmos, daisy, dianthus, echinacea (coneflower), gladiolus, marigold, petunia, and phlox. Overall, 150 species of plants in 40 different families have been recorded as hosts of aster yellows vectored by the aster leafhopper.
To acquire and transmit the aster yellows mycoplasma, the aster leafhopper must feed for a prolonged period (at least two hours) on an infected host (either locally or in a southern state). Next, the pathogen must incubate within the leafhopper for about 3 weeks before it can be transmitted to another plant. Because of the extensive incubation period, the disease is rarely spread from plant to plant within a commercial field. Thus, the primary method for transmission of aster yellows to a host in Minnesota is by the migrant adults already carrying the pathogen.
Management in home gardens includes promptly destroying and discarding diseased plants to prevent further spread. Also remove weeds because they may act as reservoirs for the microorganism. Chemical sprays to control the leafhoppers in home gardens are not practical and are not recommended.
You can attempt to protect your garden plants by placing oat straw mulch or aluminum mulch around your plants. Oat straw is probably difficult to find for most people. If you decide to use aluminum you can use ordinary foil cut into strips. The idea for this is to have something that is light in color. Aster leafhoppers use UV light to help orient themselves to fly up when they first take off. They then look for green and dark surfaces to land. When they encounter a garden with light-colored mulch, the UV light repels and confuses them so they literally don't know if they coming or going.
The highest incidence of aster yellows occurs in the spring when aster leafhoppers first arrive in May so have mulch in place by then. Add new mulch as the old material ages and becomes darker (dark mulch is less effective in repelling leafhoppers). Using mulch is not a cure-all but it can help reduce the incidence of leafhoppers in the garden.
Published in Yard & Garden Line News, Volume 2, Number 15, September 1, 2000