# Managing Armillaria root rot



## Woodsrun (Feb 12, 2006)

Recently, I identified this disease on two sites. The sites are characterized as poor with lots of exposure. One site, in particular, is a small arboretum in a historic cemetery; so it's a substantial problem. 

Does anyone have any helpful tips for dealing with Armillaria root rot? I've read to tear out the stumps, ferilize (???), mulch, water, and anything in general to promote the health and intergrity. Also, what species are more resistent to this disease? Thanks.


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## treeseer (Feb 13, 2006)

Need more info. How much infection is on the trees? A 32" white oak here had it; I disinfected the infection site on the trunk and inoculated the rootzone with beneficial microorganisms. A year later no symptoms.

Trees can codit armillaria like anything else. No need to cut em down in many cases.


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## Tree Machine (Feb 13, 2006)

Make sure that what you're dealing with is truly _Armillaria_. This fungus is one of those rare, opportunistic pathogens, a true parasite that can and does infect the living tissue of a tree. Almost all wood decay fungi are _saprophytic_, meaning they live and feed on non-living wood. _Armillaria_, however, usually starts on a dead part and can cross over and begin decay on the living parts. Very unusual, biologically speaking, for a fungus to be parasitic.

I'm curious as to how you identified _Armillaria_. Being that we're in the midst of Winter, there would be no fruit bodies present. Decay in the roots can be from just about any terrestrial higher fungi if the roots were already dead and would then not be cause for concern for the rest of the otherwise healthy trees. The big question, then, is did a single specie of fungus invade and begin killing the tree, or did something else kill the tree parts, opening them up to invasion of whatever other fungus happened to be present?

Did you carefully check the tree for a lightning strike?


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## Tree Machine (Feb 13, 2006)

By the way, Welcome to the site, Woodsrun!


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## Woodsrun (Feb 13, 2006)

*Armillaria*

That is a good question and I have limited experience diagnosing this disorder, however, I was able to identify the rhizomes growing underneath the bark, cut into the rhizomes and they were white on the inside, whitish layer growing into the sapwood (it's hard to say if this is the mycelial fan), sapwood is spoongy or waterlogged, heartwood appears to be rotting. These symptoms have steered me in the direction of Armillaria. The regional pathologist is on jury duty and can't visit the site for some time. 

Right now, we're concerned about the structural intergrity of the trees and the associated liabilities. The park manager's first reaction is to cut em' down. Most of the infected species are white oaks. One, in particular, you can see right through the butt log. That's interesting to note that with proper treatment in certain situations we can mitigate the impact and spread. 

Appreciate your input. I'm a consulting forester by trade, and delve into the arborist world on weekends; so any help is greatly appreciated. One last questions: We have our own nursery on site, and continue to plant mixed hardwoods throughout the property; I was wondering whether or not certain species are more resistent. I've had trouble locating this information.


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## Tree Machine (Feb 13, 2006)

We appreciate you coming here and asking.

First, the term you use, _rhizome_ is misused, but you're close. A rhizome is a subterranean plant stem that can give rise to roots and shoots. Plants that send out rhizomes as a means of propagating themselves tend to send them out from one point and as the rhizome lengthens, it generally branches off in different directions an a 'fan-like' manner. The term you were looking for is _rhizomorph_, a common term to describe what you saw; something like this:


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## Tree Machine (Feb 13, 2006)

When a fungal spore germinates, the living strand that comes out is called _hyphae_ (high-fay). When the hyphae increase in mass, it is then referred to as _mycelium_, and it can take on different forms, or colors. The mycelium can be cottony, filamentous or if the hyphal filaments branch, and those branches continue to branch, the mycelium is described as rhizomorphic (having the form of rhizomes) and are occasionally referred to as 'rhizomorphs'.

This is probably much more than you wanted to know about early fungal structure, but I'm a geek and this stuff has always fascinated me.

Anyway, many, many species of fungi start their life cycle from spore in much the same way; germination, hyphal development and growth, and they spend most all of their life in this form- mycelium. The mycelium produces powerful enzmes, usually cellulases, but often lignases and some both. 

To identify the fungus by mycelium alone is next to impossible, unless you plate it out on nutrient agar, attain a pure culture, propagate it on sterilized substrate and fruit it out. This is not at all difficult to do if you have the lab facilities and knowledge, but it can take weeks or months to get fruitbody production. There are hundreds of species whose mycelium is white and rhizomorphic. The color of _Armillaria_ mycelium is often more cream-to-honey colored, but can be brown, dark rust or black, so you can increase the probability of identification by that. I've never seen it to be a true white. Whenever I find _Armillaria_ (not very often) I do a bark peel and note the form and color of the mycelium, as well as the smell (farinaceous and slightly sharp and acrid). _Armillaria_ does like oak, but so do a lot of other species of fungus.

The true ID can only be done by 1) DNA profile or 2) Fruitbody structure, gill color (white) and spore color (also white). You need a microscope to see the spores, or create a sporeprint on both white and colored paper with the cap of a mushroom whose stem has been cut off. Armillaria produces abundant white spores.

_Armillaria_ (_Armillaria mellea_) tends to grow in clusters, but not always is brownish-tan-honey color, holds it's veil on the stem after the cap opens and can grow out of the tree itself, or out of the soil where a root is near the surface but very often at the stump-soil line. The stem is usually stringy and rather tough to break (does not snap off easily or cleanly) This is an edible mushroom and is really very good pan-fried in butter (not margarine) and a little salt. Keep the heat high and keep em moving. The caps are better than the stems as the outside of the stem, as mentioned before, is kinda tough and stringy.

This most certainly is more than you wanted to know.


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## Woodsrun (Feb 13, 2006)

Truer words haven't been spoken about armallaria. Thanks for the knowledge breakdown, that was great. Your making me second guess myself. What I have found look like shoestrings. The inside is white-like. There is a whitish layer that is found growing through the cambium and into the sapwood. I've also seen the shoestrings growing inside the hollow void in a red maple. 

So far, I've found this evidence on two sites located on separate sides of the river. On both sites mainly the mature white oaks are the primary target. Sites are characterized by ridgetop sites with both Northern and Southern aspects. 

One site is an upscale development; the other is a historic cemetery. It's fun puttin' the pieces together. Thanks.


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