Is this a bad plant tumor on the Rudabeckia?
Great question! Those are bud galls caused by a midge - nothing bad. You can see more images here: https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/adv... There is one at the bottom of the page of a gall cut in half where you can see the midge larva.
Although they are somewhat unsightly, they tend to not affect overall plant health - especially of mature stands of plants. Control measures are often not needed, and numbers usually vary year after year (you may see them this year, but none next year). If the plants are young and galls are numerous, or if the galls keep coming back year after year, damage may occur. You can read more about galls here: https://extension.umn.edu/yard-and-garden-insects/insect-and-mite-galls#aphids-and-midges-1346964
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Thank you so much for the information. I will hope for no galls next year.
Sure thing. Thank you for using Ask an Expert!