Knock Out Rose and Black Spot
I have 10 well-established knock-out roses in my garden. They all have good access to sunlight and air circulation. Since I moved to Houston, I have never had any problems with my roses and they were prefectly OK. This year, I have noticed that all of my roses got black spots on their leaves. I have tried Bayer fungicide for roses, another fungicide with Sulphur smell and color, and vinegar. I removed dead leaves and cut the dead/infected branches a week ago.
1- I know that there are different organic recipes for the black spot with different outcomes. What's the best practice you think would be? I am not crazy about full bloom roses. As long as my roses survive and bloom next year, I am all happy.
2- I used to water the roses once in 5 days early morning for 30 min. I was advised that I should water more so I now I am doing it every other days. Do you think that my watering schedule promote the problem?
3- In Houston there is a record-high drought and there have not been rain since mid-may to mid-Aug. I wonder, when there is not much rain around, why the roses got black spot? In contrary last year when there was more rain, my roses stayed quite OK.
I would really appreciate your feedback.