You might check my post entitled "Another Discussion (Sorry) About Eradicating Black Spot." One of the posters suggested a method for controlling black spot that I used successfully. Most of the products on the market are designed to prevent black spot not eliminate it once you have it. I started by using Mancozeb every 5 days for three weeks. It appears to be a very harsh chemical but it did a number on black spot. Thereafter, I used a variety of preventatives, such as Serenade, potassium bicarbonate and sodium bicarbonate. Potassium bicarbonate is less harsh than the sodium version and doesn't burn my rose leaves. I live on Hawaii Island at 2300 feet above sea level. Usually, it is temperate with low humidity. However, we occasionally get downpours. I use one of the preventatives once a week or so and always after it rains.
Many of the members on this forum just live with black spot and enjoy the rose flowers, which do not seem to be negatively impacted. I respect this "method" and it is undoubtedly safer for the environment. I just got tired of looking at mostly leafless rose bushes.
