HG: Homegrown Column November 15, 2008

We have two very large globe willows that have (just in the past few weeks) decided to have dead leaves. This is not the usual fall changing of colors and falling leaves, these are in various parts of the trees. The leaves have just withered and dried up.
Are the trees dying or what can we do to save the trees?
— Joan

I have three possibilities to explain what is going on with your willows.

First, we’ve had a lot of problems this summer with spider mites on willows. These teeny-tiny little guys suck the sap from the leaves, which turns the leaf a dull, brownish, bronzy-green. The leaves then fall off the tree in great abundance.

This has been going on for the past couple of months here in the valley.

If this is what’s going on, there’s not much to do about the problem right now. Spider mites aren’t life-threatening to the tree but they do put it under stress, which can open the door for more serious problems to get started.

One of these more serious problems — cytospora canker and frothy flux — is the second possibility.

The fungus disease called cytospora canker is common in this area and attacks trees that are weak or under stress for one reason or another. It plugs up and kills the vascular tissue, using it to spread throughout the tree.

Direct evidence of this disease is extremely difficult to find so we look for certain symptoms in the tree. Sudden death or die-back of branches (often while the dead leaves hang onto the branch) is the most common thing I’ll look for.

The easiest way to differentiate this from spider mites is whether the leaves fall off or not. This is not perfect, but the leaves always drop off with mites while they hang on most of the time with the disease.
Cytospora will always cause die back of the twigs and branches. Sometimes it’s fast and sometimes slow, but those branches will die off.

Unfortunately, if cytospora is your problem, there’s little you can do to stop the fungus from killing your tree.

About the only thing to do is to try to keep the tree as strong and healthy as you can. Don’t overwater the tree.

Contrary to common belief, globe willows don’t want constant water. Soak them deeply when you do water, but allow the soil to dry out a bit before soaking it again.

Avoid any obvious physical stress or damage and fertilize the tree next spring in late April with a high nitrogen, slow-release fertilizer.

The last possibility, frothy flux, is an organism that ferments the inner bark of the tree, often forming a bubbly, frothy ooze that smells sour, like stale beer.

The ooze isn’t always present. It’s typical for it to come and go, though the disease is always there. If this is the problem, you should have noticed some of the ooze in the past year or two.

We can cut this infection out if you know where the oozing is. Let me know and I’ll fill you in on the details if that’s the problem.

I am looking for a miniature pine tree that grows to about 5–7 feet tall. Do you have a tree or does such a tree exist?
Thank you.
— Jeremy

I’m assume you are looking for something with an upright, conical growth habit like the big pines we have.

The only pine that comes to mind is a variety of mugo pine called “tannenbaum.” This is a wonderful
variety and I planted one in my yard last year.

This plant often makes a lot more sense than the Austrian and ponderosa pines we plant in our yards that too often get much bigger than the area we’ve given them.

Tannenbaum grows pretty slowly, but it will get bigger than what you’ve indicated. I’d expect it to top out at 12–15 feet in height at maturity.

Remember that there’s a time aspect to all this. Look for it to reach this size in 15–25 years.

Another possibility that’s not a pine is dwarf Alberta spruce. This is a fairly common plant in the Grand Valley.

These guys form very dense perfect little Christmas trees. It will get 7–8 feet tall in old age.

The only quirk about it is that it prefers shade, at least in the afternoon. There are a few growing in full sun but it tends to be the exception rather than the rule.

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



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