I think you'll agree this is a beautiful rose. What you're looking at is a Rugosa rose by the name of 'Therese Bugnet'. I've had it for about 20 years now and just love when it's in bloom.
Last year, however, I started noticing that the upper half of many canes were dying. I just figured they snapped during a windstorm or something along those lines and proceeded to prune off the dead canes.
This shows some of the damage.
By the end of the garden season, I started noticing that many canes had swollen areas on them (see photo at bottom). After doing a bit of research, I initially thought it was a type of canker, which is caused a disease. However, I've recently learned that it's likely caused by cane borers. Fortunately, the treatment for both canker and cane borers is essentially the same.
According to the Pacific Northwest Plant Disease Management Handbook, I needed to "cut and destroy infected canes well below the infected area." This also means disinfecting my pruners in between each cut.
More damage, but on a different rose.
I finally took care of it today and am so discouraged by how many canes I had to remove. But I know I'm doing the right thing. I had a little mantra I was using so I wouldn't forget to dip the pruners into a pail of bleach and water each time: "Clip... Dip. Clip... Dip." That worked pretty well.
I'm hoping the rose will come back from this huge setback and I intend to really watch for any more swollen areas on the remaining canes this season. I'm hoping I've nipped the problem in the bud, though.
I should also mention that two other roses of mine had a couple of swollen canes. That's so frustrating! So I clipped those off as well, continuing with my "clip... dip... clip... dip" mantra.
This is a cane with the swollen area.
But the painful lesson I learned is that I probably spread the disease last year by pruning off all the dead canes without sterilizing my pruners. So this is just a friendly reminder that, if you have a disease problem, disinfect your pruners every time! Also, we're not going to shred the canes I pruned off today to go into our compost pile, but will be sending them off on our next trash day. I guess I just have to learn things the hard way sometimes!
If you want to get a better look at the swollen area of the rose cane pictured at left, click on the photo. It's pretty alarming to see something like that.
I've heard that cane borers were a big problem on Rugosa roses last year and that the gardeners who care for Rose Hill in Spokane's Manito Park were dealing with this, too. For some reason it's heartening to know I'm not the only one dealing with this!
One last thing: since the water and bleach solution can cause metal blades to rust, be sure to dry them off afterwards and then spray them with a lubricant like WD-40.