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This is not a pretty picture: aster yellows

October 22, 2018

When you notice the coneflowers have made Seussical green sprouts from the cone, your first thought might be, “cool!” But then you remember coneflowers don’t emulate kids’ stories, and you likely have a problem.

I was trying to take IPhone pics of these sweet little bees that were all over the swamp sunflowers and coneflowers. The green sprouts out of the mature cone caught my eye first, and then the distorted petals. This is the disease aster yellows.

The University of Wisconsin Extension describes it well:

This disease is caused by a phytoplasma, a bacterium-like organism similar to a mycoplasma (so formerly called a mycoplasma-like organism or MLO), but which infects plants, and causes virus-like symptoms. In plants is it found only in phloem sieve cells. Its host range includes more than 300 plants species in 38 plant families of broad-leaved herbaceous plants as well as a number of grain crops such as wheat and barley.

It affects important commercial crops like lettuce, carrots, and celery, but shows itself most dramatically on Echinaceas and other ray flowered plants. I’d heard of it before since it was once thought to cause rose rosette disease, which I dealt with in Chicago. But aster yellows spreads through leaf hopper insects: “It begins developing down south early in the spring, often building up large populations in the grain fields of Missouri, Arkansas and other states. The adults will migrate on the prevailing winds and jet streams that frequently move northward in the spring, flying into the upper atmosphere to be blown hundreds of miles north before falling out onto new host plants in an area far from where they took off.

Crazy! You should just read the whole article. Symptoms in young plants can be vague, but the reproductive parts show the most sign of disease:

The flowers are frequently deformed, with under-developed petals or weird, extra growths, or a change of color

Plants exhibiting virescence don’t develop the normal color of the petals, but are green (but don’t confuse this with the normal green color of some newer cultivars, such as ‘Green Envy’!). Plants with phyllody have tufts of pale, deformed leaves, often inside the flower or in place of the petals. On coneflowers secondary flower heads are often produced on top of the primary flowers. The pathogen induces sterility, so seeds often are not produced, and those that are produced are generally not viable.

There is no cure except to destroy affected plants. I grew my Echinaceas from seeds I collected on the 47th St pedestrian bridge over Lakeshore Dr in Chicago, and hauled them here in the back of the car when we moved, babied them in a nursery bed, and transplanted them to our new house just this spring. I was loathe to kill them and so looked at what else it could be.

A teeny pest called an eriophyid mite can cause similar problems on Echinaceas only, and you can cut off the affected flowers and be ok. The mite causes the deformed sprouts but doesn’t affect the rays on the flowers. Since mine were changed, I had to assume aster yellows. I let it go a little after these photos but then had to trash them. There is one tiny seedling that sprouted nearby, and I don’t know whether it will be affected or not. I should probably pull it just in case. So keep an eye on your coneflowers, zinnias, and sunflowers since they might sound the alarm that says your veggies could be harboring it too.

Aster yellows damage on Echinacea purpurea flower

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