Aster Yellows and Coneflower Rosette Mite Disease
8/7/2023 10:08 am
Aster Yellows Disease and
Coneflower Rosette Mite Disease
Helenium 'Mardi Gras' - the party is over!
If you are like me, you will say it wrong two out of three times: Asters Yellow. Yellow Asters, Aster Yellows. However, how you say "Aster Yellows" matters less than recognizing this insidious disease, because once you see it, disposal in the trash is the only correct response. Caution or composting will only give it a chance to spread. That said, there is another insect caused disease that impacts Echinaceas (Coneflowers) that resembles Aster Yellows that calls for less drastic action. If mites are the issue, then removing the flower heads in a timely fashion may spare the spread of the disease.
The challenge: identifying which is which, because both affect coneflowers.
The Two Diseases
Aster Yellows is a virus left behind mostly by leafhoppers. Some 300 species are affected, including ornamentals such as asters, sneezeweed, sunflowers, coneflower, coreopsis, zinnia, marigold, chrysanthemum, petunia, and snapdragon. Vegetables affected may include carrot, tomato, potato, celery and garlic. "Grasses and grains also are hosts. Weeds that may harbor the disease include plantain, dandelion, and other broad-leafed weeds." missouribotanicalgarden.org This disease spreads quickly and is worse in cool, wet summers.
The main symptom of Aster Yellows is "chlorosis." "Yellowing of the leaves while the veins remain green, is a major symptom of aster yellows. Growth slows down and leaves may be smaller and more narrow than usual. Foliage is sometimes curled. Flowers may be deformed and exhibit bizarre tufts of deformed leaves inside the flower or in place of the flower. Flowers may not produce seeds. The symptoms of the disease will often differ depending upon what species is infected." missouribotanicalgarden.org. The flower may even look like a fountain shooting out other flowers, all with the same green coloring, and with petals shaped like tiny spoons.
Coneflower Rosette Mite Disease
A closely related disease caused by mites affects Echinaceas. Scientists are still sorting out the correlation, causes and impacts. missouribotanicalgarden.org. The specific symptoms of this mite caused disease? "Green to reddish-green elongated rosette-like tufts of stunted and distorted flower parts will sprout from the tops or sides of the cones of coneflowers." OSU.edu
There seem to be two keys to distinguishing the Rosette Mite Disease from Aster Yellows. Aster Yellows produces symptoms throughout the plant, on foliage as well as flowers. On the other hand, Coneflower Rosette Mite damage is confined to flower structures. Extension Illinois
With Coneflower Rosette Mite Disease, flowers typically retain "some of the original color of the cones." OSU.edu
If you are certain it is Coneflower Rosette Mite Disease, not Aster Yellows, the plant is not lost and the damage may be contained by removing impacted flowers. OSU.edu
When You Should Be Concerned About Either Disease
Whatever the cause, here are some examples of when you should be concerned and ready to act:
- The plant is not behaving normally;
- The flowers are developing in a way you have never seen before;
- The flowers may look as if they are shooting out fireworks of themselves infinitely. This is a bad and obvious sign of Aster Yellows;
- The petals are misshapen, varying in size, and the wrong color.
Evidence of the Diseases
Some pictures of Aster Yellows Disease:
Helenium 'Mardi Gras'
Some pictures of Coneflower Rosette Mite Disease:
Comparative Pictures of the Two Diseases
Decision Making - It Isn't As Easy as it Sounds
You have two choices after you evaluate your plant.
1. If you conclude it is Aster Yellows, you must pull it root and all and destroy the plant by placing it in the trash or burning it. If any part of the affected plant is left in place or composted, you risk spread of the disease. Hesitation or half-hearted efforts will not be rewarded - especially when the plant is not a coneflower. I hesitated last year with the Helenium pictured above. Half the plant bloomed perfectly last year and I let that half remain, pulling only the affected part. This year, as the first buds formed, it was evident I had made a mistake. I should have pulled the entire plant.
2. If the plant is a coneflower (Echinacea), flyspeck the plant. Does it mostly retain the color of the original? If it is all green, pull it. Note closely any change in the tuft. At the first sign that it is "shooting stars," pull it. Are the leaves skinnier than usual or curled? Lean toward pulling the plant. Also consider whether you have had any nearby experiences with Aster Yellows.
What Would You Do with this Plant?
Two weeks ago, I was confronted with this interesting bloom. It reminded me of a failed cultivar I once planted. I was tempted to let it be. I did not yet see any impact on the other blooms, still green but not odd looking to my eyes. The leaves seemed normal to me too. Then, on flyspecking, I did see what looked like sprouts beginning on some points around the edges of the tuft reminding me of the shooting stars effect of Aster Yellows. I might have chosen to wait and watch, but three factors led me to trash the plant.
First, the plant was a volunteer untrue to its lovely parent plant (Echinacea purpurea 'Katie Saul'). So it was not precious, even though I did like the cool flower coloration. Once I even shelled out big bucks for a cultivar like it that was a dud. Second, I have quite a few Echinacea 'Cheyenne White' and one remaining 'Katie Saul' nearby to protect, as well as many plants in the aster family nearby too. Third, I had pulled the aforementioned diseased Helenium 'Mardi Gras' from a couple of yards away earlier this year.
Decisions to pull plants for Aster Yellows are easy on non-Echinaceas. More nuanced decisions may be required for coneflowers. Your Extension Agent may be able to help you decide. Or you may just wish to conduct a risk analysis based on other nearby plants and any history with Aster Yellows.
Good luck to all dealing with these diseases. They seem to have been worsening over the last few years based on numerous Facebook garden postings about this phenomena.
Submitted by Liane Schleifer