I have a number of rudbeckia but I’ve got one that seems to have died from the top. The leaves are brown and the stem seems stunted. Do you know what might have caused this and what I should do? Thanks - Seneca
This could be Botrytis. This can be prevented culturally by proper spacing, good air circulation, no overhead watering and no watering late in the day so that the leaves go into the nighttime dry. The "no overhead watering" has been a bit difficult lately. You can use a fungicide, like chlorothalonil or a copper based product, but these work best as a preventative.
I would cut off the diseased leaves, and put them in the trash. Then apply a fungicide rated for botrytis according to label directions. In the fall, be sure to clean up all the leaves when the plants go dormant. - Carole, Johnson County Extension Master Gardener