For me Goldsturm was a good spreader, but not invasive. I never had a seedling problem or found any plants in other parts of the yard. Over a period of 6-7 years my original 3 plants made a 6-8 foot circle of solidly packed, but very erect stems. I never had any flopping or dying out in the center and they continued to bloom profusely without being thinned or shovel pruned since I had plenty of room for them to grow. However, the patch of Goldsturn did eventually (around the 5 year mark) develop some sort of black fungus problem. The stems would turn completely black right at bloom time. I very seldom have any kind of a mildew problem in my garden. I blamed this problem on overspray from my neighbor's excessive lawn waterings. Probably crowding was the real issue. Flowering was not impacted by the fungus, nor did the plants flop, just looked really ugly. I had always left the plants up over winter to feed the birds but the black fungus made me start cutting them back immediately after blooming. The fungus started developing earlier each year and I eventually got mad & removed them all about a month after bloomtime - on a windy day. The next year I had a few Black-eyed Susans here and there. Now some years later I have them everywhere. They are a bit of a problem, but fortunately the biggest patch colonized an area where nothing else would grow (on a small rise with very compacted unimproved clay). The other seedlings I pull out when necessary (not easy by the time I usually spot them growing through something else.) These seedling plants are not exactly the same as the original Goldsturms, with a slightly smaller bloom and wilder look, but very cheerful & so far have never had any mold problem, probably cause I am always ripping some of them out. I doubt that you will have any real trouble with Goldsturm BES if you do a little maintenance - something I never bothered with.

SEPTORIA LEAF SPOT OF RUDBECKIA The fungus Septoria rudbeckiae is one of the most common foliar pathogens of Rudbeckia (Figure 1). Symptoms Symptoms begin as small, dark brown lesions that enlarge from 1/8 to 1/4 inch in diameter. Although the lesions are usually rounded, there may be angles where leaf veins limit the spread of the fungus (Fig. 2). Symptoms of this disease may be difficult to distinguish from those of angular leaf spot of Rudbeckia. Signs Microscopic examination of the lesion will reveal black, flask-shaped structures called pycnidia that contain thousands of thread-like spores. Spores are produced in late spring and early summer, causing leaf spots on the lower leaves. The spores of the fungus are dispersed by splashing water, with lesions first appearing on lower leaves and later developing on upper leaves as the season progresses. Management To manage this disease, remove the infected leaves at the end of the growing season to reduce inoculum levels. Because leaf moisture is essential for infection to occur, increase air circulation around the foliage by properly spacing plants (and removing volunteer seedlings) to prevent over-crowding. As with other foliar disease problems, avoid overhead watering. Fungicides containing chlorothalonil or copper* may protect new growth and reduce the spread of the disease. Preventative applications of fungicides should begin in early to mid June prior to the onset of symptoms. CYLINDROSPORIUM AND RAMULARIA LEAF SPOT OF RUDBECKIA Ramularia rudbeckiae and Cylindrocladium spp. have been reported as causing leaf spots on members of the genus Rudbeckia (Fig. 3). Symptoms Development of this disease is rarely as severe as Septoria leaf spot. Symptoms include small, scattered lesions that are often angular in appearance. Signs Microscopic identification of the acervulus (in the case of Cylindrocladium) or conidia and conidiophores (for Ramularia sp.) is required to distinguish from Septoria leaf spot. Management Like Septoria leaf spot, frequent watering (due to rainfall or irrigation) that results in leaves that are wet for extended periods favors these diseases. Control consists of proper watering so that leaves are not wet for extended periods. Management is the same as for Septoria leaf spot. Here is a link that might be useful: Diseases of Rudbeckia

Black-eyed Susan (Rudbeckia) often suffers from mildews. The best defense is a good offense: buy mildew-resistent varieties and keep the plants spaced apart to encourge good airflow. Rudbeckia is considered to be a short-lived perennial, usually blooming best during its second, third and fourth year -yearlings sometimes bloom as well :) Since rudbeckia usually multiplies nicely, it is not difficult to have new plants available to replace very diseased or elderly plants. Because of the ease with which it gets mildew, I usually pull up & discard infected plants as soon as they show signs, although many gardeners simply prune the mildewy stems back and the plants apparently will bloom the following year; while other gardeners often simply purchase new plants on a triennial basis.

I sure wish someone would answer this because I have the exact same problem. Had it last year and it affected all my plants and I'm seeing it again this year already.