Rose Blindness in Corvallis
I have been growing roses for almost thirty years with no problems (except the usual, black spot etc.) The bed is a well drained mix of sand, broken down leaves and other compost, and bark and we work continually on the soil. Around three years ago, rose blindness showed up in one rose bush. Web research did not help as authors expressed that causes were not understood, or rose was improperly pruned. Slowly, an increasing number of rose blindness cases has occurred--until around five or six bushes last summer (and sometimes late in the season instead of early spring). Continuing research revealed a single author who expressed rose blindness is caused by too much nitrogen. For several years, an organic rose food (Happy Frog with mycorrhizae) was by far the most successful (cut down on disease, produced big, colorful blooms) until I couldn't locate it in our area anymore). The rose blindness, coincidently, began around the year I had to change fertilizers to a similar product. Any thoughts before I get started on 2019? We have around 25 roses; I love taking bouquets to coworkers and friends.
Thanks for your question - this is quite a stumper. The first thing I would ask is if you have tested your soil lately, and checked the pH. Improper pH can be caused by too much rain, mulches, etc. Since you noticed the change after changing fertilizer, I would definitely start with a soil test at your local extension office. When you get your results, they can give you specific information regarding your roses' needs.