Former southern Ont resident now in zone 3. Have several clumps of Magnus or Ruby Star Echinacea. Last year some clumps (in part sun) have green cones but lack petals. Happened again this year. Is it a virus and if so what to do to limit it please.
Plants in sun this year are rather short. Is this from dry conditions? Many thanks for your wonderful contributions to gardeners everywhere.
I have seen this problem myself and have wondered what caused it. Coneflower, or Echinacea, is named after the Greek word for hedgehog, echinos, because of its prickly center. From your description, your plants may be affected by Eriophyid mites. These microscopic insects live inside the flower buds and suck nutrients from the flowers causing the stunted and distorted flower parts, such as what appears to be missing petals.
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.
While there are other issues that could affect your coneflower such as Japanese beetles, aphids and earwigs, if your Magnus and Ruby Star are not growing to 30-36 inches and appear to have no petals, it is most likely mites.