Cytospora and how it can affect aspen trees

Something is wrong with our aspen trees. The bark is cracking, some of the leaves have this weird curling thing happening, and there are some round spots with an orange outline in the bark in one area. I’m not sure what’s going on or how to treat it. (I am sending photos so you can see what is happening.)

— Damein from Meeker

Thanks for sending the pics. They’re great and give me a pretty good idea of what’s going on.

First, the bark cracking for the most part is not a concern for me. It looks like most of them are from frost cracks or some physical injury that’s healing up.

I do have some concern about the round spot with the orange margin in your third picture. It looks like a localized infection of Cytospora canker. This is a serious fungal disease. In the Grand Valley, Cytospora is almost always a fatal diagnosis. But up where you are it is cooler and aspen trees are happier. I’d have some hope.

The infection looks localized, that is, it’s not spreading through the vascular tissues of the tree (like it almost always does down here). Typically, when this happens, a “canker” will form over several years. This is just a dead sunken area in the bark that usually spreads fairly slowly over time.

There’s really nothing you can do directly for this infection. The key is to keep the trees as happy and healthy as you can. Make sure they’re watered deeply and not kept soggy all the time.

It’s probably a good idea to fertilize the trees in the spring, but do it lightly. Heavy fertilizer applications can result in soft, succulent growth that can be more susceptible to disease spread.

Cytospora isn’t a terribly aggressive pathogen and if you can tilt the balance as much as you can in the tree’s favor, it can usually hold off the disease spreading quickly and killing the tree. However, if you see that happening with branches starting to die off, I’d remove the tree to reduce the chance of it infecting nearby aspens. 

The leaf curl is caused by a tiny little guy called an Eriophyid Mite. They are related to our common spider mites but they’re typically much smaller. You won’t see them without a microscope. To tell you the truth, I don’t get all that excited about them. They won’t kill the tree and really seem to have no effect on the health and growth of the tree. Really, their issue is pretty much an aesthetic one. The plant looks “weird.” 

It would be perfectly acceptable to ignore the issue. However, if you want to try to control them, you’ll want to spray next spring just as the buds are breaking open. There are a few sprays to choose from but I like a combination of a spray oil and Sevin. You will probably have to do this spray at the same time each year for several years to achieve adequate control.

I have a Giant Sacaton grass that I want to move. I thought it was OK to move in fall, but I would rather wait until the spring. Can I still do next spring if I do it very early?

— Laura

Actually, I think the best time to transplant is early spring, usually sometime in March.

You want to do it while the plant is still dormant but right before it’s due to wake up and start growing so it can settle into its new home and heal up the damage transplanting has done.

Dennis Hill is the nursery manager at Bookcliff Gardens, 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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