If you grow coneflowers, this may look familiar — the cone looks green and kind of misshapen.
If you’ve seen this before, you’ve seen aster yellows. It’s a fairly common diseases that affects a lot of flowers in the daisy family, including coneflower, black-eyed Susan, goldenrod, marigold, and zinnia.
Aster yellows is most pronounced during periods of hot weather, and I see it most in my garden when it’s wet. The disease is spread by insects — nasty little leafhoppers.
Unfortunately, the disease is more than just cosmetic — eventually your plants will succumb to it. Because aster yellows is spread by insects (and because there’s no real treatment for the disease), it’s advisable to remove infected plants as soon as you notice them — otherwise it may attack your other garden plants.