Rudbeckia Purple splotches green bumps

Asked July 3, 2020, 10:45 AM EDT

Rudbeckia fulgida that developed large purple splotches with light green bumps on some of the leaves. Has been in this spot for 3 years, not watered at all except for rain. is it Septoria leaf spot or a gall?

Sussex County Delaware

1 Response

I am unable to say what the issue is with the Rudbeckia without seeing infected leaves in person. Obviously as you know, Rudbeckia is susceptible to leaf diseases caused by fungus (Septoria) or bacteria. The green "bumps" you have on the leaves could be an insect, but I'd need to dissect the bump in order to determine the cause. I did some searching (why it has taken awhile to reply) and the "green bumps" you are noticing seems to become more common over the past few years; however, I have not been able to find where anyone has actually looked closely to the cause. Most seem to assume it is a gall forming insect that does little overall harm to the health of the plant.

Normally, you'd be able to send in a sample to the extension office in Georgetown to have your problem identified. Management options would include remove infected foliage from plants if possible when dry to reduce the amount of inoculum around your plants. This fall remove the remaining infected foliage from the area after the plants have gone dormant for the year. This will help further reduce incoculm for next spring and remove any insects overwintering in the galls on affected leaves. Next spring, you could try applying a preventative fungicide to possible reduce fungal infections. An application of an insecticide in the spring corresponding to just before you started seeing the bumps this year could help if it is an insect. Next year, assuming things are "back to normal", you could send a sample into the clinic if it reappears.

I am including a link to the clinic in case you wish to send a sample in this year. I do not know how quickly the sample would be examined because the clinic is working on a more limited basis due pandemic situation.
https://www.udel.edu/academics/colleges/canr/cooperative-extension/sustainable-production/plant-diagnostic-clinic/