Blight is a symptom that your rose bush is suffering from an infection. Older rose bushes are the most susceptible to blight. Blight can be identified by black or brown spots on the leaves of the rose bush. There is no current method for eliminating blight completely, but you can take an active approach to control the infection. Once you have the infection under control, you can take preventative measures to keep your roses healthy and looking younger.
Prune the leaves and stems of your old roses that are infected with blight. Fungus can continue to grow if the leaves and stems are allowed to remain on the rose bush.
Dry the remaining leaves on the old rose bush with a dry cloth. Too much watering, or water left sitting on leaves, can cause blight and make it worse. Drying the leaves with a cloth may take up some of your time, but it is a great way to keep blight under control. You will also want to do this carefully, as older roses are more fragile.
Use a fungicide made for use with rose bushes to keep blight from spreading. Be sure to follow the product label instructions. You will want to pay attention to the application schedule on the product label, as you will need to reapply the fungicide on a regular basis to keep the blight in check. Applying the fungicide is the same for young and old rose bushes.
Make sure your roses are spaced out. The University of Oregon recommends spacing your rose bushes far enough apart that they get adequate air circulation. This is a preventative measure to keep blight away in the future. If your old roses are not spaced out, you will want to replant them with care. Use the same type of soil and fertilizer that the old rose is used to so that the old rose isn't shocked during the transplant process.