Disease called aster yellows is affecting coneflowers in WNY; get rid of diseased plants

aster yellows on coneflower
Aster yellows caused the plant on the left to have a bizarre tuft of deformed leaves growing out of the flower. Photo courtesy Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org

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.

aster yellows disease on coneflower
Here’s another example of aster yellows disease causing deformed leaves to grow out of the top of a coneflower. Photo courtesy Paul Bachi, University of Kentucky Research and Education Center, Bugwood.org

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.

8 Comments on “Disease called aster yellows is affecting coneflowers in WNY; get rid of diseased plants

  1. Well, I got the Ash tree question answered. I had an expert look at the tree and it is an over abundance of seeds. maybe next year will get more leaves.

    I have a white fly question. What is the best way to get rid of them? I like to keep my poinsettias over to bloom next year. They were in my kitchen and I noticed white flies so, I put them out in my yard in the shade. I was hoping a natural predator would take care of them, but there are more than ever now. I want to bring them in this Fall but don’t want to bring in the white flies. any ideas? thanks.

  2. Linda, hmmm. Interesting question. I’ve never heard of seeds sprouting while still on the plant. I’m not a gardening expert, but seeds need the right conditions to sprout. You can start seeds inside without soil, but you have to mimic the conditions of soil. The instructions here advise you to wrap the seeds you want to germinate in a paper towel and keep them out of direct sunlight to fool them into thinking they’re in the soil. Seeds on a plant are in direct sunlight. Seeds also need to be kept moist (not wet, then dry off as they might if they were still on the flower.) If you again see what looks like a seed germinating while still on the flower, try to pull out what looks like a stem. Are there roots attached? If not, it’s not a seed that sprouted a new plant.

  3. Ellen, If you have an ash tree, you should have it looked at by a tree expert. An insect called the emerald ash borer is killing trees in Western New York. This is a serious problem. You need to call an expert.

  4. I have seen this sort of growth on plants like zinnia, marigold and tomatoes. I thought the seeds were sprouting because of wet weather. Do seeds sprout while still on the plant?

  5. we have an ash tree, over 30 years old, that has weird growth this year. Less leaves and all these bumpy/prickly balls instead of leaves. Do you know what this is? I was told that some years trees produce an overabundance of seeds. So, would they be seeds? can you help? Thank you, Ellen

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