From the ArcaMax Publishing, Gardening Newsletter:
http://www.arcamax.com/news/gardening/s-156746-266449
Question: This year two of my hybrid tea roses have dark, wrinkled
markings on some of the stems, and those stems are dying. There's also
a purple ring around the stems at the bud union. What's wrong?
Answer: It sounds like a type of rose canker. Many types of fungi
cause canker on roses. Although widespread in our area, canker is
rarely a serious disease. The fungus enters older rose stems through
pruning cuts and wounds in the bark. Once the plant is infected, the
bark turns yellow, wrinkles, splits and eventually dies. The purple
ring around the stem is often a sign of the infection. If only a few
branches are affected and the damage doesn't reach the bud union,
prune out the diseased stems a few inches below the last sign of
infection and destroy them. Disinfect your pruners with a 1% bleach
solution between cuttings to avoid spreading the disease. If all the
branches are infected or if the infection goes below the bud union,
remove and destroy the rosebush and plant. Canker isn't very
contagious, so it's not likely to infect any healthy roses growing
nearby. There aren't any resistant rose varieties, but you can reduce
the risk of your roses getting canker by avoiding physical damage to
the stems, making clean pruning cuts and planting in a well drained,
sunny location.