Aster yellows, a devastating disease, is taking a toll in many gardens

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Echinacea may boost people’s immune systems, but it can’t seem to strengthen its own. In many Minnesota gardens, this popular perennial, also known as purple coneflower, is succumbing to an incurable disease called aster yellows.

Has the disease hit your garden yet? Look for distorted growth, such as greenish sprouts growing from the flowers. Yellowing and stunted foliage are other symptoms.

While you’re at it, check the Rudbeckia, or black-eyed Susan; it’s susceptible, too. So are asters, cosmos, marigolds, mums and zinnias. Even carrots and many weeds get it.

The disease struck Sonata cosmos a few years ago, then spread to purple coneflowers. It’s carried from plant to plant by aster leafhoppers and survives winter in infected plants. If you find diseased plants, the only thing to do is dig them out. They won’t recover.

Chemical controls are impractical, according to Jeff Hahn, an entomologist with the University of Minnesota Extension Service. “You can spray and spray, but you only need one leafhopper to transmit it. It’s just not reasonable.”

Jeanne Weigum, who maintains nine community gardens in St. Paul as a volunteer, says her purple coneflowers have been all but wiped out by aster yellows this year.

“Is this a growing problem?” she asks. “I think I saw some of it last year, but nothing like this. I have some gardens with gaping holes where once lovely coneflowers stood.”

Bob Bystrom first noticed the disease in his garden in Grant about six years ago. “Add my garden to the list of those with purple coneflowers devastated by aster yellows,” he says. “The only consolation is I get to observe some truly amazing deformities. Many of this year’s blossoms are green with what look like tiny leaves growing from the center of the cone.”

Deb Brown, a horticulturist with the university, says the Extension service is seeing a lot of the disease. “Coneflowers have become hugely popular. Once you’ve got a nucleus of infection, there are so many susceptible plants around, it can start growing exponentially,” she says. “There’s nothing to do but rogue them out.”

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