Four years past Rudbeckia fulgida Goldsturm was planted in a new front garden. From the second year on, they develop angular black spots on the leaves killing them ground up. I believe, without a microscope, this to be a bacterial infection. At first I thought it was fungal and tried sulphur, have always cut them back to the ground each fall and last summer tried to remove the leaves as soon as I saw the black spots. Today I removed the whole plants with roots after I noticed what I think is the spread to a hydrangea (cut this back)
My question is – if I want to replant Rudbeckia could I plant new Spring 2022 or wait; or, is there a similar plant – hardy full sun, natural – with ornamental grasses, day lily, purple coral bell – that is resistant to this bacteria?
With thanks for your advice.
Thanks for contacting the Toronto Master Gardeners. As you have noted, the black spots that you are seeing on the leaves of your Rudbeckia fulgida var. sullivantii ‘Goldsturm’ could be the result of either a fungal or bacterial disease. Both of these are unlikely to kill the plants, and since both overwinter in diseased plant debris, both can be well managed by thoroughly collecting and disposing of (not in your compost if you have it) this debris in the fall or late winter. Also, bacteria tends to build up on diseased debris if the same plant is grown in the same spot year after year, so rotating plants each year can be helpful. More information can be found at these websites :
Bacterial spots, blights, and rots
Angular leaf spot (caused by a bacteria) is a common problem in the cultivar ‘Goldstrum’. This plant is also susceptible to septoria leaf spot (caused by a fungus). However there are many other varieties of Rudbeckia that are not susceptible to these diseases.
If you really want Rudbeckia fulgida var. sullivantii ‘Goldsturm’ in your garden, you could do a thorough cleanup in the late fall or early winter and plant it again in the spring and see what happens, or better yet wait a year before planting it again. Or you could try another variety of Rudbeckia instead, that is not susceptible to these diseases. These links will take other varieties to consider :
Rudbeckias : Powerhouse plants
Best of luck with your garden !