Sawflies,sawflies and carpenter bees...

t-bred(5)August 5, 2012

I wanted to post my observations from this summer in hopes to possibly help another newer grower. There is so much info out there but it can take quite a while to compare it.

What I have learned is that I seem to have two different types of sawflies that do two different types of damage. The first being the rose slug producing type that munch on the underside of leaves,and the second being the type that lays eggs under the bark of canes and damages them. The former causes unsightly leaves and the latter can really do a number by destroying feet of cane in multiples. This is the first year I've had the rose stem sawfly but it's done a lot of damage,I've had to prune several canes almost to the graft to find healthy tissue.

I also learned that the holes I have found in the cut ends of large diameter canes are home to a small little carpenter bee, when I have pruned the cane down an inch or so below the hole,there is no damage. I guess these little bees aren't so bad after all.

Just wanted to put this out there for others unsure what they may be dealing with.

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michaelg(7a NC Mts)

Thank, this is a very smart post.

The term "borer" confuses a lit of people. Holes in cut cane ends signal the relatively benign ones, which are small carpenter bees and certain beneficial pygmy wasps. These are not eating the rose stem; they are just using a small bit of it for a nursery. The SCB, which looks like a large winged black ant, eats only pollen and is a major pollinator. The tiny wasps eat aphids and other small pest insects. I stopped worrying about these 25 years ago. I don't seal cane ends, and I don't prune out the bored cane ends except during spring pruning. Maybe one out of 500 hundred of these goes deep enough to ruin a cane.

On the other hand, the rose stem sawfly larvae will ruin every infested cane unless you catch it early. Look for wilted growth tips on one or a few canes when the rest of the roses look perky. Squeeze canes a foot or two below the wilted tip, checking for hollowness. Look for girdling cuts in the bark near the tip. The villain is a white segmented worm with a black head. It does not enter cut cane ends, but comes from eggs laid near the growth tip. If not discovered and killed, it eats its way down the length of a cane.

    Bookmark   August 6, 2012 at 10:19AM
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flaurabunda(6a, Central IL)

I too have the minor holes in the ends of pruned canes; they are rarely bigger than an eighth of an inch in diameter and they don't seem to affect the roses in any negative way. I also don't bother with sealing canes.

    Bookmark   August 6, 2012 at 12:27PM
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t-bred(5)

Michaelg, thank you for adding to this in such an informative
way!

    Bookmark   August 6, 2012 at 8:43PM
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