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Patterns of butt decay in sycamores
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<Mark Goodwin>
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On the Chico State campus in Northern California, there are quite a few sycamores, including P. occidentalis, P. racemosa, and London Plane. A few (mostly P. occidentalis?)have developed butt rot in soils inhabited by Armillaria mellea. The decay has caused a hollow directly under the trunk base. There has been no sign of other fungal conks, but there are "honey mushrooms" in the vicinity of some of the trees. In most cases the trees seem firmly rooted and vigorous on top. There is evidence of past root damage by construction/root cutting. One tree died over the course of the last two years, suffering apparent leaf scorch. P. racemosa grows alongside a year-round creek, sometimes with much of its root system washed out. In most cases it seems to be very firmly rooted.

My question has to do with the habit of rooting in sycamores, along with their resistance to decay. I'm looking for information about the tolerance of these various Platanus species to death and destabilization by Armillaria or other butt rots. I read Fungal Strategies of Decay in Trees about a year or more ago, but I don't have a copy, so I don't recall if there was reference to this.
 
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<Scott Cullen>
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Reply to post by Mark Goodwin, on May 17, 2003 at 18:47:40:

Mark,

I would have thought that Armillarea would be a cambium rotter rather than a heart rotter. But don't rely on that. There is a great site at the University of Minn. or maybe Wisconsin. The Prof who maintains it is Tom Volk. Search on Tom Volk Fungi.

An interesting thing you will learn there is that A. mellea is the most pathogenic, most aggressive of the A's. You might have a less agressive species like A. gallica or A. calvescens. The west coast species and hosts vary from east coast.

We have a large American sycamore with rhizomorphs (shoestrings) of A. gallica all over the root flare. The soil is loaded with it. It is endemic in our forest soils. A. mellea rhizomorphs branch dichotomously... one into two, each into two, each into two... and A. gallica (and others) branch randomly. DNA is the way to know for sure.

A couple of studies were done after the big storm of 1987 in the UK and it seems to me that the planes (to the sycamore is Acer pseudoplatanus) were shown to remain stable with a lot of trunk decay... but you should not rely on that sketchy recollection. You could also look at the table in the back of Matheny & Clark or get in touch with the CTFRP folks.
 
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<Mark Goodwin>
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Reply to post by Scott Cullen, on May 17, 2003 at 18:47:40:

Thanks for reminding me of Tom Volk's site, which I revisited. I have long been told and read that A. mellea is the endemic species in my region (N. California). Its association with oaks in California seems to be the basis for its common name Oak Root Fungus (ORF). Apparently it coexists with Q. lobata (and other oak species?), taking a pathogenic role only when there is opportunity. Unless I'm wrong, this pathogen gains a foothold when Valley Oaks, which are adapted to hot dry summer soils, are irrigated by gardeners. Somehow there is a change in soil ecology that favors the fungus? Perhaps a competitive advantage against other soil microbes that otherwise keep it in check?
Anyway, Honey mushrooms are quite common, and many of the campus trees (mostly exotics) occupy land that was once an oak woodland. Oaks still dot the landscape. Declining Silver maples with cut roots seem to be especially attractive to the Honey Mushrooms.
I read that the mushrooms appear with the fall rains, but they reappear repeatly here anytime the weather is rainy and not blasting hot or freezing. They may be very small or quite large, but always in clumps with fused stipes.
While some woody plants exhibit the white mycelial fans beneath the bark, I have yet to see what I can identify as a rhizomorph on tree or bush. I have seen pictures of them. Perhaps it is too dry here?
While the mushrooms appear at the base of various trees, including European olive, Incense cedar, Platanus sp.,Eucalyptus sp., Acer sp., Zelkova serrata, and Pistachia chinensis, only some of these trees have shown obvious (associated?) butt rot.
The latest Platanus (in dispute whether occidentalis or London Plane) to succumb to a complex of drought, repeated anthracnose defoliation, mechanical injury, and apparent leaf scorch, had a butt rot. The buttress roots seemed to be unaffected, and it appears entry was through (long ago) pruned roots. Vascular staining is evident, so I suspect a vascular disease may have been the last blow. The pattern of heartwood decay in the butt looks like gills. The ray cells were left after the tissue between was dissolved. It is a generally brown color, lighter in some places. There is a well-defined reaction zone delimiting the heart rot. Cambium does not appear to have decay or be intruded by the heart rot. Staining appears to be in the area of functional sapwood. Stained areas are massive in the lower trunk sections, becoming irregular and more concentric further up the trunk. Staining appears in some but not all limbs. The general growth increment was much smaller beginning about 12 years ago. In the main buttress root areas of the trunk flare, where growth was greatest, the last 3 seasons of growth were much smaller. So, it seems to me that the tree shows signs of depleted storage of carbohydrates generally, with most reserves being applied to the areas closest to the main roots.
Two other large Planes have butt cavities, although generally vigorous on top. The less vigorous of the two also has some low trunk cankers and evidence that many lower limbs were removed. In all, the buttress roots appear to be intact. Honey mushrooms are not anywhere near the trunk, although they are associated with other trees nearby.
Interestingly, when a very large Water Oak fell in high wind a few years ago, with extensive columns of heartwood decay and a fractured trunk, the Honey mushrooms had a field day as soon as the tree was removed. They appeared to be feeding on the now dead roots. In some cases, Chinese pistache that decline over a number of years and are removed have many of these mushrooms during the year after they are removed. The stump grinder obviously misses a lot of roots. One still green, but declining, Pistache had a butt rot that made it look like it was standing on short stilts. There was decay into the main roots from the inside, but the cambium was alive. Another very large Pistache, which has been declining for a dozen years, has just begun having Honey mushrooms all around its base. Without excavating the root crown, I don't know if there is a butt rot, but I'd guess there is. All the Pistache trees show vascular streaking. I suspect verticillium. This species has generally been failing locally. I speculate that Armillaria may be opportunistically attacking the base of these trees, but is not the primary factor in their decline.
 
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<Scott>
posted
Reply to post by Mark Goodwin, on May 19, 2003 at 07:37:19:

I forgot to note in my first post that our big sycamore with rhizomorphs all over the root flare does not appear to be infected or colonized pathogenically. The shoestrings are just sitting on the surface of the bark.

Even if A. mellea is endemic you should try to determine if you are seeing A. mellea or a less aggressive A. species on particular trees. It might make a difference in management.

There is another Armillaria site (sorry no link) that provides a mushroom key for the A. species. Apparently field researchers check for presence in soil by cutting a fresh piece of branch (say 2" dia) and putting it in the soil like a stake. If A. is there and active rhizomorphs will grow up the stake. Dunno if time of year is critical for you (wet v dry). As I understand it the rhizomorph goes out hunting so to speak and if it finds an opening the mycelia spread from there.
 
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<Jerry>
posted
Reply to post by Mark Goodwin, on May 17, 2003 at 18:47:40:

David Lonsdale, Principles of Tree Hazard etc., refers (84) to a published "list of genera and species which appear to be resistant or tolerant to infection" in:

Greig, B.W.J., et al. 1991. Honey fungus. Forestry Commission Bulletin 100. HMSO, London.

If you have access to a good library or interlibrary loan, that might give you some useful info, though I'm not sure that interactions of English species of trees and fungus can be translated to California just like that.
 
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