Hole in rose cane

campvFebruary 1, 2013

I started trimming my roses. This rose has large dia. canes about 1". One cane was too tall so I cut off the end to shorten. Inside the cane about the size of pencil eraser was a black hollow hole. It went straight down the inside for about 2". From the outside the cane looked fine. I have never seen this before.Does any one know what caused this?

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Others will probably tell you what it is, but I will tell you that, of course, you should cut that cane to below where the hole is, to where there is healthy whitish pith.


    Bookmark   February 1, 2013 at 4:55PM
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seil zone 6b MI

Sounds like some kind of cane borer. There are a few of them so I can't tell you for sure which but as Jackie said, you want to cut that can down to good healthy center pith.

    Bookmark   February 1, 2013 at 5:52PM
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jerijen(Zone 10)

And once you've done that, since you KNOW you have had a cane borer problem, you might want to seal the end of the cane. Regular white glue is good enough.

We are told that the larvae of cane borers eat aphids . . . So they ain't all bad. :-)

We used to see them around here fairly often, when we had a lot of old "junk" lumber laying here and there on the hillside. That's gone, and so it seems are the cane borers.

Of course, since we no longer shorten canes, there's not much opportunity for cane borers, here.



    Bookmark   February 1, 2013 at 8:45PM
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Tuggy3(9b NorCal)

I use white glue, but I make sure it's the waterproof formula, not washable school glue. I'm trying thumbtacks this year. If that is a durable solution it will save some time. We prune roses for our rose society fundraiser. The people who don't seal have a lot of cane borer in this area. It doesn't seem to kill them though. We prune the same ones year after year. Mary

    Bookmark   February 2, 2013 at 12:46AM
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Thanks everyone. This was my first year with this problem and I have been growing roses for about 20. I think I was attacked this summer not sure. What months do these little varmits attack? I cut and glued all canes that had problems and thanks to all of you I know what to look for now

    Bookmark   February 2, 2013 at 3:08PM
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michaelg(7a NC Mts)

People are assuming you found a tunnel in a previously cut cane end. These tunnels are the shallow and relatively harmless nests made by tiny bees and wasps. Sealing cuts (which many growers, including me, do not bother to do) is to prevent those.

Apparently you found a tunnel that was not in a previously cut cane end. These are usually more damaging tunnels, but sealing cut canes does nothing to prevent them. The adult insects lay eggs in or on the soft growth tips at the top of the cane, then the larvae eat their way down the center pith, ruining the cane. If you had examined the part that you cut off, you might have found a larva or pupa in the tunnel that led upward. One western insect that does this is the Raspberry Horntail sawfly.

    Bookmark   February 2, 2013 at 4:22PM
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Michaelg you are right this cane flowered and was new growth. I do beleive there was some kind of black pupa in it. I never sealed the canes before when pruning. You don't think the glue idea will work? As I trimed more of the roses (I have 25) I noticed a few had the same issue but not as bad. I cut those canes down past the brown to were the pith was nice and white. This is a first for me, these roses are about 6-7 years old. How do I protect them?

    Bookmark   February 2, 2013 at 6:05PM
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michaelg(7a NC Mts)

1. Twig-nesting bees and wasps drill into freshly cut cane ends to make nests. They do not eat the rose tissue. Damage is usually minor. Sealing is to prevent these.

2. Other borers that you discover only by cutting the cane--sealing has nothing to do with these. You cannot prevent these unless with high-powered systemic insecticides. However, you can discover and kill them before they pupate and become egg-laying adults. Doing this will probably prevent it becoming a widespread problem.

The larvae are eating their way down the pith of the stem and growing as they go. Stems with boring larvae in them may have wilty tips when the rest of the roses are not wilting. They usually go blind (stop growing without setting a flower bud). You can feel the hollowness by squeezing soft or half-hardened stems. The stem sawfly adults (if that is your pest) make fine girdling cuts through the green bark of young stems when they lay their eggs. These cuts are visible, usually below the topmost leaf. So watch for these signs and cut the stem back in sections until you find the worm.

    Bookmark   February 3, 2013 at 11:06AM
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