What’s Wrong with MY Tree? PART 2: Oozing Stains on Tree Trunk
Southwest Yard & Garden by Dr. Marisa Thompson
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The stained, oozing spot is slimeflux (aka bacterial wetwood), and I bet it stinks like strong chemical paint thinner. The bad news is it’s not fixable, but it’s also not causing a problem. Slimeflux is an indicator of an underlying decay issue. Photo credit Joy E.
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Answer: Yes, I know what it is and what caused it. But no, I don’t have easy answers for how to treat it. What you’re seeing is called slimeflux, aka bacterial wetwood. If you were to smell it, you’d never forget it. It smells to me like nail polish remover that’s gone rancid. My uncle, also an arborist, said it smells like gym socks. So basically it smells like what it looks like: gross.
There is no treatment recommended for this unfortunate condition. Hosing the goo away with water doesn’t really help anything since the bacteria are living in the trunk tissue, and the stain won’t go away either.
The reason there’s no quick fix or long-term treatment is that the slimeflux is not the problem. It’s a smelly symptom that there’s an underlying issue: decaying tissue between the two trunks. This brings up a major reason why structural pruning should be done when trees are very small: to keep two branches from becoming co-dominant in the first place. When the branches were small, that narrow crotch wasn’t a problem. But because of co-dominance, both grew at the same steady rate; eventually, as each trunk became wider and wider, they started pushing against each other. Over time, if they continue to grow at the same rate, an included bark junction or “bark inclusion” can form at the base of the branches, and this creates a weak union that’s a perfect place for decay. As Dr. Ed Gilman, tree researcher and Professor Emeritus at the University of Florida, says, “Branches with bark inclusions split easily.”
Links to related columns:
Scroll down to the bottom for more pruning resource links!
OK, so now what? Like I said, I knew the cause, but not the cure. I reached out to several Certified Arborists, landscapers, landscape designers, and urban foresters across the state for their input. I depend on these long-time professionals and their expertise all the time. It was good to hear the same feedback from different angles. To sum it up, this is a major bummer of a question. The options are few and each is risky.
You can live with the aesthetic issue and try to ignore the slimeflux. Pulling back those larger rocks at the base of the trunk, confirming that there’s no plastic under the surrounding rock, adding a thick layer of fibrous or woody mulch, and confirming that irrigation water can reach the very wide root system to a depth of 2–3 feet are tactics that will help your odds. But eventually this tree is going to fail. We already know that cottonwoods are shorter-lived trees. Average lifespans may be around 40–50 years, and even shorter during droughts combined with warmer temperatures. They grow so fast they don’t have time to create very strong structures—or immune systems. Even if your tree was healthy, it may be on the way out. Depending on how bad the bark inclusion is, or how bad it gets, one of those two branches could fall and do some serious damage to surrounding structures, other plants, or people. I’m cringing just thinking of a big wind gust that whips around your yard and torques one of those huge trunks in the wrong direction.
Over-pruning of lower limbs over the years just exacerbated the problem. The branch tips are carrying too much weight, and this will be even more true once your tree leafs out completely. The natural branching structure of trees is such that the weight is distributed evenly among upper and lower branches so that a gust of wind doesn’t become a hazardous situation.
I specifically asked if one of the trunks could be removed by a certified professional, and if the rest of the tree would survive. Unfortunately, these trunks are too big at this point, and the remaining trunk might still topple over if given the opportunity.
Again, Dr. Gilman, “Drastic measures such as cabling and bracing can be taken to help hold trees with these defects together.” But these techniques require skilled, licensed professionals, and will not prolong the life of this tree indefinitely. I personally do not have experience with cabling or bracing. I’m afraid on a tree this size that, even if it’s done correctly, the risks associated with the cabling failing are too high. One local expert pointed out that most of the research that’s been done around the world on cabling and bracing has been done on trees that were healthy, not old cottonwoods that were already pushing their life expectancy. In case you go this route, I’ll share resources on these techniques and terminology on the blog too.
Several of the experts I consulted suggested you do a real risk assessment of the surrounding area, and if the risks are too high, consider having this beautiful tree removed. If you end up doing this, consider replanting with a medley of native and adapted tree—and shrub—species that have a chance at living longer lives and can also put up with our increasing average temperatures. Just to name a few: netleaf hackberry, desert willow, Osage orange, Texas red oak, Chinese pistache, lacebark elm, and honey mesquite. Through The Nature Conservancy’s Urban Conservation Program, I had the privilege of working with tree and climate experts on a year-long project called “Climate Ready Trees for Albuquerque’s Community Forest.” The final report is due to come out any day now, and you can all be sure I’ll write about it as soon as I can. Leaf it to me.
- For more on Wetwood vs. Fungal Decay research, check out these publications (email me* for PDFs if you have trouble accessing them online):
- Wetwood and Slime Flux - UMass Extension Publication
- "Bacteria in decomposing wood and their interactions with wood-decay fungi" 2016 publication by Sarah R. Johnston, Lynne Boddy, and Andrew J. Weightman
- "Decay Resistance of Elm Wetwood" 2009 by J.S. Coleman, C.W. Murdoch, R.J. Campana & W.H. Smith
- "Decay resistance owing to near-anaerobic conditions in black cottonwood wetwood" 1979 by B. J. van der Kamp, A. A. Gokhale, and R. S. Smith
- "Bacterial Species Associated with Wetwood of Elm" 1983 by Murdoch and Campana
Links to more resources:
- Pruning Information for Tree Owners from TreesAreGood.org
- Disinfecting pruning tools: Use a common household cleaner like Lysol. In studies on pruning tool disinfection, these household cleaners performed as well as bleach, but bleach was the most harmful to blade surfaces.
- Tree Pruning Techniques NMSU Guide H-156
- Pruning the Home Orchard NMSU Guide H-327
- Thinning Fruit for Tree Health
- NMSU's Pecan Extension Program pruning resources: https://aces.nmsu.edu/ces/pecans/pruning.html
- Cabling and Bracing Trees https://hort.ifas.ufl.edu/woody/Cabling.shtml
- Pruning Shade Trees in Landscapes Website FULL of resources: https://hort.ifas.ufl.edu/woody/pruning.shtml
- Developing a Preventive Pruning Program:
- Animations
- Animation of removal cut
- Animation of reduction cut
- Animation of heading cut (NOTE: CONSIDERED IMPROPER PRUNING PRACTICE ON MOST ESTABLISHED LANDSCAPE TREES!)
- Dead branch removal
For more
gardening information, including
decades of archived Southwest Yard & Garden columns, visit the NMSU
Extension Horticulture page (http://desertblooms.nmsu.edu/),
follow us on social media (@NMDesertBlooms), or contact your County Extension
office (https://aces.nmsu.edu/county).
Marisa Thompson, PhD, is the Extension Horticulture Specialist for New
Mexico State University and is based at the Agricultural Science Center at Los
Lunas.
* desertblooms@nmsu.edu
Not knowing where this is located, it's tough to say. But I would hazard a guess that this is not a native Southwestern Cottonwood, but rather that hybrid cottonless Cottonwood so many people boght in the 1970s or early 80s from mail order nurseries back east. From that point they shot up like a rocket and provided instant tree. Thereafter friends and neighbours took cuttings of whole branches and grew their own tree. I've never known these trees to be loved lived and when older and incredibly high, I've seen whole giant branches suddenly die and any wound bleed and never heal or compartmentalize properly. I did also experience this when I lived up in Anza California with a native Fremont Cottonwood seedling which was a foot high from the Whitewater wash in the Coachella Valley. It had a rough go with the temperatures in winter when branches would die towards the end of the stems. The mountain high elevation Fremonts were entirely different in form and hardiness. But when I trimmed the Desert wash Fremont, I experienced the same reaction from the wounds which always bled and never stopped.
ReplyDeleteThe other thing I notice is the Cottonwood is riparian and not necessarily in a deep soil wet location and probably has roots clear on the other side of the house looking and seeking out any additional water. I had one hybrid tree which did this as well. Amazing how far their roots will travel. They all do good when young, but as they get huge, so do their requirements. Just my two cents.