Without a photo it's very hard to know what the issue is with your roses, Mary. But if it is indeed a fungus, there are fungicides designed to treat those issues on roses.
Thank you Douglas. I'll try to get a pic posted. I treated them last week with Bayer 2in1. Will treating them with a fungicide be too much at this time?
Yes you can treat them,lowest has several products for this,also after dead heading the roses remove clippings in a bag so as not to re-contaminate affected area.
Mary, you'll need to check the label on the Bayer. There should be an indication about how long to wait before applying anything else.
Bayer 2 in 1 works systemically, through the roots, and is a fertilizer with an insecticide. Bayer 3 in 1 has the fungicide too. I think you have to keep using it for it to work correctly and eradicate the fungus. To help keep new fungus from spreading before the Bayer kicks in, a couple things can be used on the leaves that are organic and won't hurt even with the Bayer. If you have powdery Mildew, spray the leaves with milk, it really does work! Do it once or twice a week If it has Rust, a spray of Baking Soda and water-1 1/2 teaspoons per quart of water- also once a week, can prevent it from getting out of control. Leaf Spot or Black Spot are able to be kept controllable with 1/4 teaspoon of white or cider vinegar in a quart of water. Once a week. Spray when the temperatures are below 85 and in the morning or evening not in the middle of the day when it is hottest. Do not spray all of these at once either! Maybe a day or so apart if you have all three diseases. Then there are products from organic companies that also really work, Planet Natural; Gardens Alive; and there is something called Actinovate is a new organic fungicide I have found online, and at one of my local Garden Centers, which works too. Don't use other products that are chemical fungicides, until you wait for the time limit on what the label on the Bayer recommends. Only use the organic ones listed above. I take care of a few hundred roses in several gardens a week, using only these organic measures, but I also use other plant health building practices which help them stay disease free. And They are very very healthy, no diseases, no chemicals.
Have a ??? on the amount of vinegar to use for black spot. Is the 1/4 teaspoon in a quart of water the correct measurements? It seems like so little vinegar for the amount of water?
make shure that when you dead head or prune knockout roses that you remove these clippings or you will re-introduce the infection back in the area again
I do not know what formula you're referring to Mary, but there are some here:http://www.organicrosecare.org/articles/recipe_mildew_control.php