Hello Jennifer,
I'm not confident that your echinacea has aster yellows, although the cone flower is susceptible to that disease. Did the flowers bloom normally and then develop poorly developed petals, or did they develop as I see them now? 

There's no way to tell for sure whether a plant has aster yellows except to have it diagnosed in a lab. There are conditions that can mimic aster yellows but are not as deadly, such as spray from an herbicide or insecticide, insect damage such as by the Eriophyide mite, or lack of certain soil nutrients that can cause yellowing leaves.

From what I see in the pictures, my guess is that the problem isn't aster yellows. I would remove any yellow leaves and clean any debris from the soil. To be on the safe side, you may want to remove the flower stems and dispose of them in the trash. Observe the plants for any new growth and see if the problem still exists. Aster yellows will not kill the plants but will live in them for the life of the plant. This causes a danger to the rest of the plants in the garden.

I have included three articles on this subject. Even though they give some of the same information, they also include great pictures and examples of aster yellows. You can compare them to what you see in your garden. If the problem persists, you may want to send a sample of your plant to MSU's plant diagnostic lab --- www.pestid.msu.edu --- for a definitive diagnosis. 

https://bygl.osu.edu/node/816

https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/insects-pests-and-problems/diseases/viruses/aster-yellows

https://extension.umn.edu/plant-diseases/aster-yellows

I hope this helps but don't hesitate to contact us again if you have questions or need more information.

Good luck with your coneflowers!

This is the way that the flowers developed, to my knowledge. They never bloomed what I would say is a “normal” set of petals. They’re all half-petals and jagged at the tips. Someone mentioned that earwigs may be eating the petals at night? Do you think that is a possibility? I haven’t seen the farmer across the road use a pesticide yet this season, that doesn’t mean he hasn’t though. I’ll dispose of the stems and heads at the end of season as suggested. Do you recommend doing that before they go to seed? Or is it ok to let the birds eat whatever seeds may develop? 
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I know I've been giving you a lot to read, but I found this article from the Toronto Master Gardeners. I think it answers your questions about how to address your coneflower problem. Yes, earwigs can be a problem with your plants, but I don't believe your plants have aster yellows. Most likely it is insect damage or rosette mites, which means your plants should be fine next year. I would not leave the seed heads for the birds because they could carry pests and diseases to other plants.

While there are other issues that could affect your coneflower such as Japanese beetles, aphids and earwigs there are two serious problems that affect coneflowers: Coneflower Rosette Mite and the phytoplasma disease known as Aster Yellows.

The coneflower rosette mites live inside the developing flower buds and suck nutrients from the base of the flower causing the stunted and distorted flower parts, such as what appears to be missing petals.

Aster Yellow disease is caused by a phytoplasma. This small specialized bacterium which is spread by from plant to plant by sucking insects, infects the plant phloem tissue. The phloem tissue is responsible for conducting food that is made through photosynthesis from the leaves to all other parts of the plant. As a result, symptoms of aster yellows include chlorotic, curled foliage; stunted stems; and bizarrely distorted flower parts.

Since the overall health of your plant doesn’t seem to be affected, I believe that your coneflower is affected by Coneflower Rosette mites. It is important to cut back the infected plants to the ground in the fall and remove all plant parts from the area to prevent re-infestation next year. It is also important to not compost these plant parts, but instead to place them in a black plastic bag and dispose of them in your garbage.”

Ohio State University has an excellent fact sheet titled Coneflower Cleanup which illustrates the effect of the two diseases on the coneflower.

https://www.torontomastergardeners.ca/askagardener/echinacea-disease-pest/

Thank you for your questions about echinacea. I love coneflowers and have enjoyed discovering new information about their care while researching your question.

Have a great summer.