Hello, every year my rose leaves develop black spots. I am careful with my watering and remove the diseased leaves and also feed my roses during the summer. I would like to take steps to prevent the start of black spot. Would applying dormant spray to my roses now assist me with this.
Yes you can apply dormant oil spray to your roses before the buds break and when the temperature will remain at 0°C (32°F) or above for a minimum of 24 hours. See the link below for a previous response indicating the culture practises related to black spot on roses.
Good luck with your roses this year.