Roses forum→Sunburn or canker?

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Name: Rosemary
Sacramento, CA (Zone 9b)
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reh0622
Sep 30, 2019 10:52 AM CST
My question first, can healthy canes become sunburned after leaves have fallen off for one reason or another? Or is the darkening, say on one side only a sure sign of canker?
Coastal Southern California (Zone 13a)
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jerijen
Sep 30, 2019 5:35 PM CST
Rosemary, I think you'd have to show us a photo or two.
Name: Rosemary
Sacramento, CA (Zone 9b)
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reh0622
Oct 1, 2019 12:43 PM CST
My ph. is not co-operating right now, but on one of the tree roses, it has stopped blooming and lost most of it's leaves which is a bad sign. The others aren't blooming, either, but had gone semi-dormant most of the summer. They are in much better shape as far as a leaf cover goes. The more I look at them, the more I think it is canker since my other two tree roses which are only a few years old have no similar canes and are all green.

When my ph. re-charges, maybe I can post some photos. Just wondering if you had ever heard/seen canes that had recently been deadheaded, look sunburned on one side and have it not be canker. I guess they wouldn't be healthy if they could!
Name: Porkpal
Richmond, TX
Charter ATP Member Dog Lover Cat Lover Keeper of Poultry Keeps Horses I was one of the first 300 contributors to the plant database!
Garden Ideas: Level 2 Plant Identifier Raises cows Roses Farmer Celebrating Gardening: 2015
porkpal
Oct 1, 2019 12:55 PM CST
I have plenty of semi-leafless canes; I ought to go look at mine.
Porkpal
Name: Rosemary
Sacramento, CA (Zone 9b)
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reh0622
Oct 1, 2019 1:48 PM CST
Here are some typical examples:
Thumb of 2019-10-01/reh0622/7c4b16
Thumb of 2019-10-01/reh0622/7cd3a0
Thumb of 2019-10-01/reh0622/5aed81
Thumb of 2019-10-01/reh0622/b25a2d
Thumb of 2019-10-01/reh0622/746f38

Name: Rosemary
Sacramento, CA (Zone 9b)
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reh0622
Oct 1, 2019 2:01 PM CST
Here are a couple more:
Thumb of 2019-10-01/reh0622/e998fe
Thumb of 2019-10-01/reh0622/1e26d3

What is interesting is that they are the normal green on the opposite side of the stems.
Name: Rosemary
Sacramento, CA (Zone 9b)
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reh0622
Oct 21, 2019 12:56 PM CST
Since posting this, I did some research and found some answers. The darkening can be due to a variety of reasons besides canker and sunburn. Blackspot, powdery mildew and downey mildew also can affect the canes with black and brown and splotchy areas.

One other sign it's canker are sunken areas, but also where the cane connects to a larger cane or the base, it usually bulges out a bit. New growth is lackluster, leaves frequently yellowing and there being few blossoms, sometimes being stunted, etc.

So I've been looking at all the bushes I take care more carefully, and I've spotted canker I was unaware of.

Most of the books say to prune it out 5" under the affected part, and then disinfect the pruning shears with 90% isopropyl alcohol, or a chlorine solution at 1 part chlorine and 9 parts water.

So this has given me another question. What if you are deadheading a bush that has canker somewhere below where the blooms are but where there is no obvious sign of canker at the point of deadheading, can you still pass it on to another bush as you continue deadheading? Does anyone know? Thank You!



Name: seil
St Clair Shores, MI (Zone 6a)
Roses Garden Photography Region: Michigan
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seilMI
Oct 21, 2019 4:52 PM CST
To answer your question, yes, roses can sunburn. That usually occurs when they are in very hot, dry, direct sunlight for a prolonged period of time. And, as you say, do not have leaf coverage for shade.

In looking at your pictures I'd say you have a variety of things going on here. Some of those very black canes are die back. For what reason I don't know but the cane has died and turned black and should be removed. I would also remove any canes with what looks like an open wound on it. Some of the canes look like they are just aging and turning barky which is normal as they mature. Some of the purpley spots are probably black spot or mildew. You should remove them and, if you wish, use a fungicide to prevent it from coming back.

On the question of spreading diseases, yes, they say you should disinfect your pruners between cuts. Whether the plant is infected further up from the visible signs is uncertain. However, if the plant is already showing symptoms the entire plant has already been exposed to the spores anyway. I have never used disinfecting between every cut. It would take me for ever to prune my paltry sum of 75 roses if I did so. Besides, all of the spores for these fungal diseases are already present everywhere. They are in the soil, mulch, air, water and neighboring plants. They are only waiting for the exact right conditions to emerge to show up on the roses. You can disinfect everything and they will still be there ready to pounce when the weather agrees with them.
Name: Rosemary
Sacramento, CA (Zone 9b)
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reh0622
Oct 21, 2019 6:39 PM CST
Thank you, seil, for sharing your knowledge. It sounds pretty hopeless. Guess prevention trying to keep them super healthy so they won't be susceptible is the best way. Think I'll wait 'til pruning time to remove the worse...most of one Mr. Lincoln I have had since I first planted roses 25 yrs. ago. I just noticed that one this past week. I've been trying to rejuvenate it for the past 5 yrs.--removing old canes, weeding, mulching, feeding, etc. That will leave one cane that looks healthy...I think.

When you say "open wound", do you mean the cane has a place of separation in it?

I did read that canes affected with sunburn, canker, black spots on the cane should be pruned off in winter/spring pruning.

I am wondering if anyone knows whether or not there are any rose species that rarely or never get canker.
Name: seil
St Clair Shores, MI (Zone 6a)
Roses Garden Photography Region: Michigan
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seilMI
Oct 21, 2019 7:28 PM CST
It isn't all that bad, Rosemary. Yes, rose diseases are everywhere and we all battle one form or another but all in all the roses do pretty well anyway. You have to learn to let go of the idea that your roses should be perfect all the time and just start enjoying the lovely blooms when ever they happen. No one's roses are perfect all the time. Yes, it's nice when they look all leafy and healthy but I don't grow roses for the leaves. I grow them for the beautiful blooms! And I've found even totally leafless they bloom anyway, lol! They are survivors.

I would suggest you do some experimenting. We often have black spot that over winters on the canes as those dark areas. Sometimes, if the cane looks otherwise healthy and has growth buds starting, I will leave the cane and see how it grows. It may grow and bloom just fine and show no other symptoms. If it seems like it is not preforming well you can always prune it off later.

In pictures 3 and 4 it looks like the bark is split open. That is what I mean by open wounds. Those should be removed to prevent borers and other insects from entering.

You have lovely roses so stop fretting and spend more time enjoying them!
Name: Rosemary
Sacramento, CA (Zone 9b)
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reh0622
Oct 21, 2019 8:57 PM CST
Thank you for the encouragement, Seil. Since becoming involved in the care of a public garden, I want to take care of it in the best way possible to help the bushes thrive, but I suspect some may be harboring canker somewhere and that's why they are not very robust, as well as my own that have seen better days, and all the bagged bareroots I had bought from Lowe's that have or are succumbing to canker. I had to ask myself if I spread the canker unknowingly when I didn't know what I was dealing with after first planting them and enjoying their first blooms (except for a couple that never took off), If one had canker, and I pruned off obvious canker and didn't disinfect the pruning shears, did I unwittingly spread it to others is my question. As of now, of the ones remaining, I see serious canker on all of them. I am much more observant and careful now. I have around a 100 bushes now (including my own) to take care of, and I do disinfect after if I suspect any canker on a cane or stem I deadhead or prune off. I am a little paranoid about it, but it's better to be over-cautious than oblivious, right? And I do take time to smell the roses (even though I think I am allergic to the pollen!), and admire the uniqueness of the interesting variety of blooms!
















Name: Rosemary
Sacramento, CA (Zone 9b)
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reh0622
Oct 24, 2019 11:50 AM CST
I did some research on rose canker and found out there are 5 different kinds! The good news is that it can be prevented with fungicides that treat blackspot, according to two sources if there are already signs of it, in which case it needs to be pruned out (and the pruners disinfected before going onto another bush) before it spreads on the bush in question.

The bad news is that if it gets into the graft area, the bud union, it's only a matter of time before the entire bush is going to be ailing and finally die with no cure.

I'm noticing a lot of what looks like canker to me on rose bushes that are not blooming that well and have some yellowing foliage.

Once source said to take cuttings above cane area that is cankered, and root them for a new bush, but I'm not so sure if that would be canker-free according to seil's post above. Maybe it would only be a ticking time bomb in the new bush, if the cuttings succeed. I guess that would take some experimentation and observation.

Already I'm detecting some ominous signs in the Francis Meilland that I bought bareroot from Regan. Were the beginning signs there and I didn't notice? Or did it get transferred from other affected roses just through the deadheading process without sterilizing the hand pruners going from one bush to the next. Or was it caused from some other way, through tainted potting soil or mulch, etc. I'm also noticing two galls which have begun. Fortunately, galls do not usually cause the bush to die, I read (although I thought it was the cause of one of my tree roses). When I prune FM this winter, I may take cuttings that look canker free as far as blotches, if I can find some, and see if they root and remain canker-free.
[Last edited by reh0622 - Oct 24, 2019 1:05 PM (+)]
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