Do you mean she has cankers developing at the pruning cuts, or elsewhere? It's very common to have canker at the pruning site that kills the bark on the pruning stub and then stops at the leaf joint below--actively growing canes have an immune system that can contain cankers.

If the cankers are elsewhere on the canes, chances are they are inactive and have been there since winter or spring. I doubt you would have significant development of cankers during the California summer. Canker fungi like it cool and wet, and are most active when the plants are dormant or semi-dormant.

This is not something you need to fear spreading through the garden like wildfire. In my climate, canker spores are probably everywhere in the garden. I don't worry about it. I avoid winter protection and dormant pruning. I cut well below a canker if it girdles more than 50% of the circumference. That's pretty rare.

Last year abt. this time, we had weeks of rain and fog, and cool weather... I decided to prune the roses, and wound up w/canker that affected most of them, some died because it girdled the canes, some still have it but only parially around the canes. I had never seen nor heard of this stuff, so researched, and learned that it's always present and comes to life in the right conditions, and is spread by using dirty clippers... and that is what I had been doing, i sterilize my clippers before pruning and then go out and work my way thru' abt. 100 roses, and succeeded in spreading the canker.... now I carry a coffee can w/alcohol and dip the pruners after each clip- 'clip and dip'-- 'clip and dip'-- and it seems to work, I don't have any canker spread.... I carry the coffee can of alcohol and the clippers in a pail so it is convenient, and leave the clippers in the alcohol to soak when I take a break..and I don't prune when the weather is wet and cool... sally

I talked to her again. She saw the canker damage on the canes ( not the tips) in the trimmings on the ground as she was cleaning up after pruning. It looked like discolored and dying tissue and split open and swollen places on canes. What she did was recut the stems and dip the pruners in bleach water after each cut. Then she cleaned all the mulch away from the bed to bare soil and washed the canes and the soil with the hose and let it dry in the sun. We were wondering if she should re mulch after spraying with a fungicide to kill any canker hanging around the canes. I'm glad this isn't something that could travel down the canes and wipe out all her roses. Many of them came from family members and from an out of state property her parents owned. Thanks for all of your help. I know she wouldn't come here to ask so I said I would find out what she should do.

I've had canker kill many teeny roses in the springs here, so it can be a big problem. Older roses that can take some pruning are fine. It depends on how many canes there are, imho. The little bands don't have much room to spare, whereas my established roses can lose a lot of cane and be good later.

I do sterilize my pruners during 'canker season', and I make sure that the soil near the base of the plant has air circulation and nothing that can hold too much moisture near the canes. When it gets drier here later in the season, I add mulch for the year. (Most of my roses don't need winter protection from cold, so I really do pull the mulch and leaves away in winter to keep the warm, drizzly days from causing outbreaks.)

I do use fungicide for a few weeks in spring on susceptible plants. Otherwise I'm mostly no-spray. I think the spray helps, but I do it all in combination now, so take it for what it's worth :)

Canker knows how to spread itself without help from pruners. It produces airborne spores. I don't sterilize except for RRD, and I have a canker-prone climate, but canker is not a big problem. However, as Meredith said, it does pose a danger to band plants and rooted cuttings during cool wet weather.

Thanks again to everyone. I am going to start using these suggestions in my own garden. I went and looked over my roses and saw that on a Kathryn Morely which had long canes that I did not prune last year there was damage where there was rubbing and thorns tearing the canes. These appeared as small black and brown patches with irregular edges. They are at the wind facing side of the plant and are scattered like leopard spots but not encircling the cane. I didn't see any lower down where the canes don't blow around. She described her HT affected canes as big areas of black death and the canes swelling and splitting with whole canes dying. Mine sounds minimal. I didn't even know it was even there until I went out and looked for it. That is the only rose showing it now but I guess it could pop up anytime.