Black Spots or Black Leaves on Rudbeckia
(In His Garden)
Rudbeckia Black Spots: Doug. I wonder if anyone else is having this problem?
My Black eyed Susan's emerges from the ground and promptly get black spots all over the leafs. Is this a blight? Same last year. Do I need to sterilize the soil? How? You asked for ideas... hopefully this one with catch your fancy.
Rudbeckia can get several different diseases very quickly and they show up as black spots. Botrytis or Powdery mildew both show up as black spots on leaves eventually. This is a wicked plant for getting these problems. However...
What concerns me is that your plant emerges from the ground and gets the problem instantly. This tells me you likely have the plant situated in too much morning shade or have too much moisture around the crowns or are watering too heavily (like an automated sprinkler system).
A Plant For Dry Areas
This is a plant of the dry areas - almost droughty fields rather than the moist rich garden soils.
It is a plant of full hot sunshine with little shade (although it will survive in part shade)
So if you're having problems, I suspect it is based on cultural conditions. And while some gardeners might be able to get away with a little too much moisture or little light, the combinations of things in your garden is creating this problem.
With some perennials, you can fudge the lowered light or higher moisture. Rudbeckia is not usually one of them or you'll pay for it with plant health.
You don't need to sterilize the soil. You need to move the plant to a full hot sun, dryland condition. :-)