Prevention should start early in the season, or you may find that you are struggling to eliminate the disease for the rest of the year. The Ortho Fungicide is your best tool for prevention (or any Fungicide with Propinconazole in it, such as Banner Maxx). Start spraying as soon as the first leaves are fully developed and be faithful about applying Fungicide every 7-10 days. If you start early and continue without fail, you can have a disease free garden.

Also, you can spray your roses with Liquid Sulfer Fungicide immediately after you prune the roses in late Winter. (Prune your roses no later than the time that Forsythia is at peak bloom) Spraying with Sulfer before the roses start to leaf out will kill disease spores and dramatically reduce the amount of infection by Blackspot.

In the meantime, continue with the Ortho spraying and you should be able to get the disease problem under control. Good luck!

Another thing you can do in the late winter is remove all the old mulch and replace with new to get rid of fungus spores on the ground. It has been the biggest year ever for BS around here.

Can I soak the mulch around the roses now with something to kill the spores? Some other product? (I use Ortho on my roses too.)
It will cost me a fortune to remove the old mulch and put down new (now or later), because my gardens are so big. I've put down several truckloads of it to amend heavy clay.

earlybird,
I have the same problem as you; many cubic meters of redwood bark mulch which is too expensive to remove and replace every year. Thats why I recommend spraying right after the Winter pruning with Sulfer. Apply liberally on the mulch surface as well to eliminate as many spores as possible. It does work.

Some of the things I've come to believe about blackspot - mostly based on reliable studies from university extension services, but also on my own observations:

Backspot spores are heavier than air and are not especially mobile. If you can get the spore count very low in your garden, you will likely have little or no disease until the spore population builds up again - something which is 100% certain to happen, eventually. In a northern zone 5 garden, most roses will be pruned almost to ground level in early spring. This means that the major source of spores, and eventual reinfection, is on the ground or in the mulch, in your rose bed. These spores get onto your roses mostly by being splashed up, either by rain or by hose water. The simplest thing is to add a light layer of fresh mulch. Most of the spores on the ground or in the old mulch will thereby be prevented from splashing onto your plants. In my garden, adding a fresh layer of almost any mulch, right after spring pruning, will often, but not always, keep blackspot away until early July. I imagine I could get similar results by spraying the ground or old mulch with lime sulfur or with just elemental sulfur. As long as you restrict the spray to the ground, you could use these sprays anytime during the season. Spraying the plants afterward with water would remove almost any possibility of damage to your roses.

Now, here's my major point: If you don't want to use modern synthetic fungicides at all, the above may be helpful and give you greater control. But if you do plan to use synthetic fungicides, your most important action is what trospero recommends,

"Start spraying as soon as the first leaves are fully developed and be faithful about applying Fungicide every 7-10 days. If you start early and continue without fail, you can have a disease free garden."

Thanks so much. I've never heard of the sulfur sprays but I will make a note to get some.

forensicmon,
Make no mistake, the Sulfer sprays are a compliment to the Ortho fungicide spray program, not an alternative to. Both are needed to effect total disease control during the growing season. :-)

THANKS!

I wanted to input here. I used the 3 in 1 last year and had a horrible BS problem by the fall(started in July). This year I used the Bayer Advanced Disease Control every 2-2.5 weeks and no BS at all. Good luck!

The 3-1 only works in conjunction with spray, in my experience. I don't use it anymore because it's expensive and includes a lot of insecticide.

The sulphur spray is usually done in the winter because it can damage foliage. You can spray the mulch as well as the canes. I also spray the mulch under my roses with the regular in season fungicide (Bayer Advanced Disease Control). I start spraying that as soon as the roses leaf out and then every 3 weeks until first frost.

I'm with sunnishine. Before I found the GW Forum, I used the 3-in-1 exclusively. Lots of BS. Lots of defoliation.

Last year I stopped using the 3-in-1 but started spraying with Advnaced Disease Contol, but too late in the season. Some BS, not a ton of defoliation.

This year I only use the Bayer Advanced Disease Control every 2 weeks, starting early in the season. Very little BS, no defoliation at all.

If you have a bad bs infection get some Manzate,zinc manganese. It will kill the blackspot spores. Use it twice a week for three weeks to bring it under control, then switch to Bayer Rose Disease control or Banner Max to keep you protected. That is what I use and I have been disease free all season in spite of all the rain we've had.