by Connie Oswald Stofko
Margaret Raupp, coordinator of Open Gardens, brought to my attention a couple plant problems that she noticed around Western New York this summer.
Last week we talked about the lily leaf beetle, which is damaging lilies.
This week we’ll discuss aster yellows disease, which affects coneflowers and causes the blossom to be deformed.
“I saw it everywhere and most gardeners were not aware of it,” Raupp said.
Bizarre green tufts growing out of the flower are actually deformed coneflower leaves erupting out of the blossom, according to information on aster yellows disease from Cornell University.
Another symptom is foliage that turns yellow while the veins stay green.
Aster yellows is a disease is caused by a microsopic organism called a phytoplasma. It is spread by small insects called leafhoppers. As a leafhopper sucks the sap of the plant, it spreads the disease to that plant. If the leafhopper skips a plant, that plant will be fine.
So the good news is that if you are visited by leafhoppers, you might not lose all your coneflowers to aster yellows disease.
The bad news is that there is no treatment for the disease. Any plant that is affected has to be pulled up and thrown in the garbage, said John Farfaglia, extension educator with Cornell Cooperative Extension in Niagara County. Don’t throw plants with this disease on your compost pile.
Remove the plants promptly to contain the spread of the disease.
While we’ve been noticing it on coneflowers, aster yellows can affect more than 300 species of plants, according to information from the Missouri Botanical Garden. One plant is the annual aster, which turns yellow (hence the name of the disease).
Other ornamental plants include zinnia, marigold, chrysanthemum, petunia and snapdragon. Edibles affected include lettuce, carrot, tomato and celery. Grasses and grains also are hosts. Weeds that may harbor the disease include plantain, dandelion and other broad-leafed weeds.
The spread of aster yellows is worse in cool, wet summers, according to the Missouri Botanical Garden, and that’s the kind of weather we’ve had this year.
The leafhopper that spreads the disease migrates northward each summer on storm fronts out of the south, according to Cornell. You never know when, where, or if this leafhopper might drop out of the sky and into your garden.
If you find plants with aster yellows disease, pull the plant up and throw it away immediately. You might also want to choose plants that are less susceptible to this disease.
A few more tips from the Missouri Botanical Garden:
- Vegetable growers may protect susceptible crops by using mesh fabrics that keep leafhoppers and other insects away from the plants.
- Some growers put strips of aluminum foil between rows because bright reflections of sunlight confuse the leafhoppers.
- Remove weeds in your lawn, garden and surrounding areas, including plantain and dandelion that may harbor the disease.
If you have more questions about diseased plants, contact Cornell Cooperative Extension in your county.