HG: Homegrown Column October 04, 2008

I live in Colorado Springs and my quaking aspen trees have a fungus/mold called armillaria in the ground and it is killing all plants around the trees. What do I use to get rid of it?
— Deb

Well, you’ve got a toughie, I’m afraid.

There is no cure for severely affected plants. Any plants that are showing significant symptoms should be removed and destroyed as soon as possible.

We essentially have no fungicides that can help. Any control measures you employ are meant to simply stop (or at least slow down) the spread of the disease.

When you remove any infected plants, it’s important to remove and destroy (by burning or getting them into the trash) all of the stump and root system, even small roots, because the fungus can live in this infected debris for many years and infect any new plants you put in that area.

You’ll also need to keep a close eye on all existing plants in the area because plants with a healthy appearance growing near obviously diseased plants may be infected but not showing symptoms, yet.

Anything that starts to show symptoms should be removed immediately.

Now, all is not necessarily lost!

Any trees and shrubs which are not seriously affected may be helped.

The first thing to do is to make sure your remaining plants are as happy and healthy as you can make them.

This disease most often strikes plants that are weak and under stress.

Also, be especially careful not to overwater your plants because armillaria thrives under moist conditions.

When you do water, make sure that the soil is wetted deeply, but allow the soil to dry a bit before watering again. Don’t allow water to pool around the base of the plant.

It’s also a good idea to fertilize your plants in the spring with a slow release, high nitrogen fertilizer.

If you have some plants that look healthy but perhaps are showing the first symptoms of infection, you might consider removing the soil from around the base of the plant, exposing the tops of the larger roots.

Again, keep any standing water out of this area and keep it dry. These roots should be left exposed during summer, but cover them over in the fall with some loose soil before it starts freezing in the fall.

When it comes time to replant, there are some plants that show some resistance to armillaria. I wouldn’t count on immunity, though, as there are several species of this fungus that tend to attack different plants.

Remember, the important thing is to create a soil environment that’s less favorable to the disease and more favorable to your plants. You can check for lists online. Some of the more common plants on them that we can grow are barberry, Oregon grape, fragrant sumac, redbud, hackberry, Washington hawthorn, ginkgo, honeylocust, Kentucky coffee tree and Austrian pine.

I was wanting to know when is the best time of year to transplant mums? The plants came up from seed about 2 years ago, but I like them to be in a different place.
— Kim

Most people transplant mums early in the spring (March) before they start their growth for the year.

You can do it later on this fall (October) but you might miss out on some of the flowers you could have enjoyed.


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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