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Cane Borers: A Public Service Announcement

Cane Borers: A Public Service Announcement

Fri, February 15, 2019 by Lucy Contreras, Horticulturist and Rosarian | in Botanical Gardens

This is a public service announcement. It has been brought to my attention that your roses may be at risk. Cane borers may be taking up residence in your garden. This is not a drill. I repeat, this is not a drill. Please bear with me as you are provided necessary background information regarding the threat at hand…

Despite February being a short month, it is one of my most jam packed. It’s rose pruning season! In our area, this coincides with Valentine’s Day. I know, can you get any cheesier? Love it or hate it, it’s hard not to think of roses. Depending on where in the country you live, you may prune earlier or later, but the general rule of thumb is to prune when the Forsythia begin to flower. Luckily, we are right on time.

Horticulture volunteers, Wanda Johnson and Theresa Parker, donned gauntlet style rose gloves and joined me for a rose pruning tour of Brookgreen Gardens. Our stops included the Poetry Garden, Upper Right Wing, Oak Allée, the White Garden, the Palmetto Garden, and the Lachicotte Greenhouse. We may not get as many swooning fans as The Beatles, but I’m sure if the roses could cheer, they would. Pruning isn’t only good to rejuvenate your plants, but it also puts you up close and personal with them. This is a great opportunity to really see what’s going on and if there are any problems that need to be addressed.

As we pruned, our focus was on the removal of anything that was dead, damaged, or diseased. After each cut, we took note of the pith, or the center of the stem that assists in transporting nutrients, making sure it was healthy and white, as pictured above. However, if the stem had disease, the pith would appear brown or black. While a darkened pith may be alarming, I find a hollow pith to be even more jarring. This brings us to our public service announcement:

A hollow pith may be indicative of disease that has rotted the pith down, but sometimes, it can be something even more nefarious. Okay, maybe I’m being dramatic. Maybe it’s on par with diseased stems. What is setting off all these alarms? Boring insects. Don’t let your guard down, these are not some dull bugs lounging in your rose’s stems. These insects bore into the cane, causing damage to your roses. They can weaken, and in extreme cases, even cause the death of the plant.

Is it the end of the world, or your rose, that you have cane borers? No way. This is easy to remedy. Remember how we said a healthy pith is white? Simply cut down to your next outward facing bud, and once you have reached that healthy pith, you have removed the borer. Same goes for disease! No bug spray or other chemicals needed.

So what are these insects? They may be a type of wasp, beetle, or moth. Some cane boring wasps are even predators of aphids. This puts me in a conundrum, since I love insects that hunt aphids, but I can’t support their housing needs. What a vicious cycle. Cane boring insects are generally looking for a safe place to lay their eggs. In this case, the rose offers some protection and even a snack once the larvae hatch. The picture above illustrates a cross section where the damaged or diseased pith meets healthy pith.

Cleanliness is next to godliness and that is hardly more true than with roses. Make sure you dispose of the infested rose debris properly. Do not include it in any compost or reincorporate it in any way back into your garden. If you are still feeling uneasy about the prospect of cane borers calling your roses home, you can simply put a dab of Elmer’s Glue on each pruned cane. If you go this route, make sure to get glue that will not wash off. While this is not a method I practice, it is not without merit.

This has been a public service announcement.

See you in the gardens!


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1931 Brookgreen Drive

Murrells Inlet, SC 29576

Off US Highway 17 Bypass, between Murrells Inlet and Pawleys Island