My annual battle with aster yellows has begun, and if you're a perennial gardener, you're probably dealing with it, too.
It's a bad year for the disease. Coneflowers are the most visible victim. Telltale signs are distorted flowers with missing or discolored petals. Often flowers remain green, with extra-large centers.
Aster yellows is spread by a leaf hopper that rides the winds north each summer from the southern U.S. to Minnesota. This year those leaf hoppers arrived early, University of Minnesota Extension educator Michelle Grabowski told a group of Master Gardeners two weeks ago. The bugs, which are olive green and less than 1/5 of an inch long, spread the disease by feeding on the plants. By the time you notice aster yellows in the garden, plants have been infected for at least three weeks. So there's not a lot you can do to prevent it.
The best thing to do is to remove infected plants. Coneflowers grow in bunches and while it may be tempting to remove only the visibly diseased stems, Grabowski said it's wise to take out the entire plant. Plants that have aster yellows won't get better, and by leaving inflected plants in the garden you're just encouraging the spread of the disease.
Aster yellows also affects plants that include asters, marigolds and goldenrod as well as vegetables like carrots, which when infected grow distorted leaves and hairy, bitter roots.
Here's more information on the disease from the U of M:

blog.lib.umn.edu/efans/ygnews/2012/07/aster-yellows-common-in-cone-f.html

www.vegedge.umn.edu/VEGPEST/aster.htm

When I first saw aster yellows in my garden years ago, I was heartbroken at the loss of plants, especially coneflowers. Fortunately they are prolific self-seeders, and aster yellows isn't carried over in seeds. I usually have a few healthy plants make it through the summer and rely on new seedlings for big purple flowers in the next year.
And we can always hope aster yellows isn't so bad next year. It all depends on the weather. Fingers crossed!