SteveM I've never seen rust on a dahlia or even a photo of confirmed rust on a dahlia
Ohhh, ok, I may have ended up in the wrong place — I’ll let her know. Her grow space is indoors, and very warm actually, but comparing to your photos will be amazing, thank you!
SteveM Just in case it is fungal and she is ventilating the plants with a fan, I would make sure this plant is last in line so it won't spread spores.
I’m so glad you included this note — seemingly obvious, but I hadn’t thought of it. She is ventilating, and this plant is very close to the end, but I’ll share your suggestion in case she might want to move it to the very end! Thank you! 💓