Either tebuconazole (Bayer Disease Control for Roses etc) or propiconazole (Banner Maxx, Fertilome Systemic Fungicide) applied every two weeks will give excellent control under severe blackspot conditions. Bayer Disease Control costs $15/quart and is available at some Lowe's or online. The main environmental concern is that it can leach into groundwater in sandy-soil areas, although I doubt that this would be an issue at the scale of homeowner use. "Non-controversial" is in the eye of the beholder, but these products appear to be safer than many earlier synthetic fungicides.

Michael's given you the two best fungicides available. Either one will work but the Bayer is easier to get and cheaper. The best way to prevent an out break is to start a regular spray schedule in the early spring and keep with it.

Two fungicides that are considered "organic" are Serenade and Green Cure. You have to use them faithfully every two weeks starting BEFORE you see symptoms and at the cure rate not the control rate for them to be effective. Seranade is available at Walmart and Green Cure is online only.

So called "organics" doesn't mean they are chemical free. They maybe less toxic but they are all still chemicals of somekind and should be handled carefully.

I suspect most of us here are trying to get by on as little spraying as possible.

I find that when the temps stay up in the 90s-100s (or higher!) for any length of time that it is just too darned hot for BS to form, therefore I do not spray at all in July and August. I figure why spray preventively when there is nothing to prevent because of the heat?

Kate

The following recent research paper may be of interest.

Here is a link that might be useful: recent research

Is is being suggested that July and August are BS-free if the temp. is over -say- 90?? My experience is that BS occurs no matter what the temp. is, even with some OGRs, which are usually more BS resistant... I no longer spray my over-100 roses, but some are almost defoliated, and I am gradually replacing them w/more resistant types... and have observed that China roses do very well no-spray, some better than others.... but it doesn't seem to matter what the temp. is, I think the humidity has more to do with it and notice when the humidity is higher the BS is worse.. and here in coastal central Fla., it is usually quite high....ie: more BS......sally

My worst months are July and August because it is hot AND humid here then. Seems to be perfect growing conditions for BS.

May have to do with different regions. Kansas gets very hot during July and August, and I often complain of the humidity, but maybe the humidity isn't as bad as some places further south--I couldn't say. All I know is that BS tends to form in the 70 and 80 degree temps, and I don't usually need to spray during July and August when our temps are in the 90-100+ range. When it cools off in the fall and we have more moisture, I usually need to start spraying again, although I never spray a lot.

Of course, I don't let a rose on my property usually unless it has good BS resistance, so that may be another reason why I can skip sprayings during the really, really hot months.

But like I said, maybe these are regional differences. What works for me may not work for you in another region.

Kate

Thank you for all the good advice. I have been growing old roses for a dozen years or so and while my bourbons and hperps certainly defoliate in late summer, most of them are so strong they bounce back--so I've never really bothered with spraying. But last fall I decided to plunge into HTs (out of nostalgia I think since they remind me of the world I grew up in) and I understand they many of them will suffer to the point of death if their bspot goes untreated. So I've much to learn as I enter into this new area. Thanks!

Black spot rarely is the outright cause of death. It may be the death knell of a rose that is already ailing from some other reason but on an otherwise healthy rose even total defoliation from it shouldn't kill it. A weakened rose from constant defoliation may not winter as well either because it won't have had those leaves to bulid energy reserves for the spring. If your roses are healthy, well fed and watered they should come through an occasional outbreak just fine.

Repeated defoliation depletes the plant's energy reserves so there are less sugars available for antifreeze and less to drive regrowth in the spring. So blackspot can lead to smaller, weaker plants and winter losses. This is less of a concern with naturally hardier and more vigorous roses such as hybrid perpetuals.