Poplar borer can damage structure of aspen trees

Two of our aspen trees aren’t looking very good. There are some small holes in the trunk and there is some stringy stuff coming out. There also is a lot of dark sap oozing as well. It looks like varnish. I’m afraid this is a borer of some sort. Any clue what causes this and ideas for a potential remedy?

— Kirby and Bess

What you’re seeing is poplar borer damage to the tree. It’s not that uncommon and I don’t consider it to be an emergency. This borer does most of its feeding in the heartwood of the tree (which is already dead tissue).

They can very occasionally tunnel through the cambium layer of the tree which is a bigger problem, but that’s pretty rare.

It is worth doing something about, though. Their damage can structurally weaken the tree to the point that a gust of wind can snap it off, and their holes can provide an opening for Cytospora canker, which is a much bigger concern. 

Treating these guys will take some persistence. The treatment itself is a spray of the trunk with 38 percent Permethrin. Usually one spray a year about the first of July will do it. You can apply a second spray a month later if you really want to be sure. This borer has a two- to three-year life cycle so you’ll need to continue spraying for three or four years, at least, to get rid of them.

My husband and I have a patio made out of stones set into dirt. This year we were thinking about planting some type of ground cover (perhaps Irish moss) to grow between the stones. The area gets sun most of the day and shade part of the day and needs to be able to stand up to high traffic. What ground cover would you recommend? We would prefer something that we could grow from seed directly in the dirt of the patio.

— Joan

I’m afraid Irish moss would struggle under the conditions you mention. It really does best where it gets either dappled shade or at least shade in the afternoon.

Too much of our heat, low humidity and intense sunlight will cause it to burn and languish. It never seems to thrive and fill in the way we hope.

A better option would be wooly thyme. It does great in sun and heat, stays very prostrate, and smells wonderful when stepped on. I’m afraid you’ll have to use plants in this area — I’m not aware of a good solid perennial ground cover that you can do from seed.

One way to economize is to divide bigger plants into several smaller ones. Now don’t be too greedy here. Trying to stretch them too far often leads to failure of the plant. You want to make sure there is a good cluster of both stems and roots connected together.


I have an Austrian copper rose bush, and last year a long branch came out on it that is red, like a Paul scarlet climber. Is it possible that this was a grafted rose and this was its original rose? I’m really not complaining, it is very pretty. Please let me know what you think happened.

— Lorraine

Austrian copper roses, unlike most all the other “species” type roses, are always grafted. Most all that type of rose are grown on its own roots to help improve its cold hardiness, but Austrian copper has the bad habit of suckering terribly if grown on its own root.

Given good soil and adequate water it will form an impenetrable bramble as big as your yard! I’m sure what you’re seeing is a sucker from the rootstock. I recommend cutting it off since that rootstock rose can get a bit out of control, and it can compete with your Austrian copper and crowd it out.

Dennis Hill is the nursery manager at Bookcliff Gardens, bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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