When and how do I start treating roses for black spot? —Sandra Jennings, Cleveland, OH 


Most roses—particularly hybrid teas—are susceptible to black spot, a fungal disease that can be devastating. If you already have roses with this problem, remove all spotted leaves from the plants (as well as any that have fallen to the soil) throughout the growing season. Before winter dormancy, get rid of infected leaves and trim or remove canes that show the same spotting.

Avoid overhead watering, especially late in the day, as moist conditions encourage the spread of black spot lesions. Make sure your roses are planted in sunny, exposed sites with good air movement so they’ll dry rapidly after rainfall. And next time you shop for roses, look for cultivars with some resistance to black spot.

In spring, once new foliage starts to unfurl, you may wish to begin a spray program with a recommended fungicide. (Check with your local cooperative extension service or a trusted garden center to find out which one is best for your location.) Fungicides won’t reverse damage that’s already present. They’re a helpful preventative, though, particularly during wet weather, when you can apply them as often as once a week.