Aster Yellows vs. Eriophyid Mites on Coneflower

We’ve been getting a few calls lately from northern gardeners wondering if their coneflowers have aster yellows. That’s one option—the other is an Eriophyid mite infestation. Here’s what you need to know about these two plant problems.

Aster Yellows

coneflower with mites?

What do you think? Aster yellows or eriophyid mites?

This disease is fairly common and can occur on many plants, including tomatoes, marigolds, snapdragons, even lettuce—but it’s most often noted here on coneflowers. The plant will show signs of decline, such as stunted growth or damage to the leaves. But the most dramatic symptom is the crazy, deformed flowers on the plant. The plant may have growths out of its cone or tufts of green where the purple petals should be. The growths can be very strange looking. I’ve even seen coneflowers with petals growing out of the center of their cones!

Aster yellows is caused by a phytoplasma that is spread to the plant by aster leaf hoppers, when they feed on the plants. The disease tends to be more common during hot years, which would explain why we’re hearing more about it this year.

Aster yellows is not curable and it can spread, so the best thing to do is remove the diseased plant and throw it away. Do not add it to your compost. If you have several coneflowers and only one or two are showing symptoms, don’t remove the others, but keep an eye on them next season for signs of trouble.

Eriophyid Mites

There are many types of eriophyid mites and they can cause a variety of galls and growths on plants.  The most common one on coneflowers is the coneflower rosette mite. It’s called that because it produces a rosette like growth on the cone of the coneflower. The growth may be green and may even send up shoots similar to aster yellows.

The mites are microscopic and live inside the flower bud as it develops, sucking nutrients from the plant. The cone of the coneflower often sprouts the rosette and petals around the rosette may fade. To treat for eriophyid mites, remove the flowers and do not compost. You can treat plants with a horticultural oil or a miticide before bud break. For now, the best treatment is to remove the infected flowers and clean up the garden well this fall.

Side-by-Side Comparison

For an excellent side-by-side comparison with photos of aster yellows and eriophyid mites on coneflowers, check out this page from Ohio State University.

6 Comments

  1. Hermione on August 9, 2021 at 7:40 pm

    I have a mix of coneflowers in my garden. Every year I grow lots of them and sometimes they even grow on their own. I buy them always on https://gardenseedsmarket.com/coneflower-black-eyed-susan-cosmos-seeds-of-2-species.html same as other seeds. Actually, all of them look gorgeous and fit perfectly to my garden!

  2. Barbara Gasterland on August 12, 2021 at 7:22 pm

    Thanks for the link to the comparison page at Ohio state. Very helpful to diagnose what’s going on.

    • Mary Lahr Schier on August 12, 2021 at 7:24 pm

      Happy to help! It’s one of the most useful sites we’ve seen for identifying what the problem is with coneflowers.

  3. Dianna Dunn on August 12, 2021 at 7:35 pm

    Thank you for the information. I haven’t noticed any as of yet.

  4. Sandi Zickrick on August 22, 2021 at 2:52 pm

    Where do the mites over-winter?

    • Mary Lahr Schier on August 23, 2021 at 7:53 pm

      Good question! The females overwinter under bark or in protected sites near the host plant.

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