Trichoderma and Hypoxylon Canker

Shella McBride and David Appel in their article on Hypoxylon Canker for AgriLife Extension state that once Hypoxylon Canker is evident, it is usually too late to save the tree.  The Arborlogical Services web site says that it is extremely rare to see Hypoxylon Canker on the trunk of a tree and have the tree recover or survive.  The Hypoxylon Canker article on the Texas Forest Service web site is even direr.  It says that once the tree is actively infected, the tree will die. It also says that there is no known cure.

In the spring of 2011 during that record Texas drought, we removed two large branches from a large Red Oak (Quercus shumardii) on a client’s property in Grey Forest, TX.  The client is a landscape architect and a winner of ISAT’s Best Development of the Year award many years ago.  One of the two branches had Hypoxylon cankers on it and the other was dead, but had no cankers.  One of the cankers on the live branch was closer than 12 inches from the main trunk and we were hoping to remove the branch before the disease reached the main trunk.  During the next inspection of the tree we became aware that we had not been successful as a canker had developed just below the branch cut on the main trunk.  We did a drench with corn meal water applied at the base of the tree.  Our mix was one cup stone ground corn meal per gallon of water and we let it soak for several hours.  We applied about 15 gallons of the corn meal water at the base of the tree.

The client took over with the treatments, applying a drench annually.  A few years later we did an Oak Wilt injection on several Live Oaks on the property and we did a corn meal drench on the Red Oak at the same time.  We also removed several large dead branches from the Red Oak that did not have any disease cankers present.  The client’s opinion of this Red Oak in June 2019 from the point of view of a landscape architect is “the tree looks great.”  That is survival and recovery.

Two years ago in 2017 we injected a large number of Live Oaks on a property in Boerne, TX for Oak Wilt.  The clients were both dentists and were raising horses trained for barrel racing for their daughters’ racing team.  Trees with no diagnostic Oak Wilt symptoms were flagged with blue, trees with symptoms were flagged with yellow, and two Live Oaks with Hypoxylon Canker were flagged with red and were not injected.  The two oaks with Hypoxylon Canker did receive a corn meal water drench as did all of the trees that were injected with Alamo.  All of the treated trees had also been drenched with corn meal water by the client several weeks before we did the injections and our corn meal water drench.

An inspection in 2018 revealed that 3 of the yellow flagged trees did not survive.  All of the surviving trees were drenched in 2018 by the client and they plan on drenching again this year.  All of the blue flagged trees have survived two years, the remaining yellow flagged trees have survived, and the two red flagged trees have survived.  The two Hypoxylon Canker infected trees not only survived, they look better this year than they did when they were first treated in 2017 (in my opinion).  That’s survival.  The jury is still out on recovery.

Systemically Induced Resistance (SIR) or Induced Resistance (IR) using Trichoderma obtained from soaking whole ground or stone ground corn meal in water is showing promise for treating tree diseases.  This is not peer reviewed research.  It is just me playing with an idea based in science on a problem that is considered lethal with no treatment, no cure.  It is anecdotal, but it is working.  I’m 3 for 3.  Actually, I’m 4 for 4.  We treated another Red Oak with corn meal water at the South West School of Art that survived a year plus.  It looked great when it was removed for a building expansion.   I will probably soon make Dr. Linda Chalker-Scott’s list of Myths in Arboriculture.

Hopefully others will start playing with SIR or IR so we can see if I’m just lucky or we have something here that will help us with our care of trees.  Trichoderma is not our only SIR weapon, but it is easy to use, very low risk, and inexpensive.  Finding a tree infected with Hypoxylon Canker that you do not need to remove is rare.  Give it a try when you find that rare tree that is worth the effort.  Try it on some of the other diseases you encounter that are difficult to manage and see if it helps.  Trichoderma  is reported to be effective against Phytophthora and Armillaria.

David M. Vaughan
Certified Arborist TX 0118
ArborVaughan Consult, LLC

Trichoderma and Systemically Induced Resistance

At the 2015 ITC in Orlando Florida the last talk of the conference was by Dr. Glen Percival on Systemically Induced Resistance (SIR).  He reported on his research using the fungus Trichoderma to successfully treat Apple Scab and Armillaria spp. in Great Britain.

At the 2016 ITC in Washington D.C., two studies done in Italy were presented using Trichoderma to treat diseases.  One treated tree was an historic veteran.  They grew the disease organism found in the veteran tree, tested some 60 different strains of Trichoderma in vetro and picked the best performers to apply to the tree.  In both of the studies, Trichoderma suppressed the disease issues.

At the 2017 ITC in Columbus OH, Dr. Glen Percival presented another study in which Trichoderma suppressed Armillaria.  His talk was on the Use of Biologicals and Their Potential for Soil Borne Disease Management.

At the Oak Wilt Qualification course in Fredericksburg TX September 2017, Gene Gehring stated that he often only needs to do a single application of propiconizol and is able to follow up in two years with fertilization to help with the recovery process.  He does a second application of propiconizol only when he has recurring symptoms, which is not often.

In June of 2014, we had treated 5 Oak Wilt symptomatic Live Oaks in San Antonio with Alamo (a propiconizol product) applied at 20 ml/dbh, injected into roots and root collar.  One of the Live Oaks was about 50-60% defoliated (we recommended not treating), three had abundant symptomatic leaves (veinal necrosis) with good canopies and the fifth did not have symptoms but was within 50 feet of the symptomatic trees.  All trees responded well to the injections and stabilized.

The next year (2015) a June inspection discovered all five trees with symptomatic leaves and we recommended re-treatment.  The client declined.  I was aware that the organic folks used Trichoderma from whole ground cornmeal to suppress fungal diseases in tomatoes and asked the client if they would let me try cornmeal water and cornmeal broadcast to see if we could get a SIR reaction for Oak Wilt.  Since it was free, they agreed.

For the cornmeal water or tea, we used one cup whole ground cornmeal per gallon of water.  We let the cornmeal soak in the water for about 6 hours and then dumped the cornmeal water in the shallow trench around the base of each tree, the well we created with the air spade to expose flare and roots.

We used two buckets or 10 gallons per tree.   On the fifth tree, we also did a broadcast under the entire branch spread of the tree using 20#/1000 square feet.

I returned in two months to inspect the treated trees and there were no symptomatic leaves on any of the five Live Oaks, in the tree or on the ground.

In 2016, we again treated all five Live Oaks with a cornmeal drench, but I charged for the treatment, $125 plus tax for 5 trees.  By then we no longer used the broadcast method because of issues with squirrels, deer, and fire ants.  We had another year with no symptoms.  All trees were stable but all look like they have battled Oak Wilt.

In 2017, the client decided to do the treatment themselves and save the $125.  The trees were stable in 2017 and 2018. (Keep in mind Gene’s experience about a single treatment being effective and all that is needed).

Since 2015, we have used a cornmeal drench with every injection that we do.  We have the client do follow up annual drenches.  So far, we have not had to do a second injection on any Live Oaks that have been treated this way.  A note: we do very few injections for Oak Wilt, so this is not much of a survey.

When a client declines injection, we have tried just using cornmeal water alone and the results have been mixed.  In my opinion, just using the Trichoderma is not reliable. Just the SIR reaction does not appear to be enough to reliably suppress Oak Wilt.   Our success has been drenching in conjunction with Alamo injection.

Another note of caution, this is not science and in no way even approaches a controlled study.  It is purely anecdotal.  The nice thing is that it costs almost nothing.  We can buy 50# of whole ground cornmeal for $10.  If you buy from a good nursery it will cost $20.  Put some bay leaves in the bag to keep out the flower beetles and you can treat a lot of trees with $10 of product.  You can mix the buckets while you wait for the trees to take up the propiconizol injection, and dump the water after you remove the tubing.  The cornmeal only needs to soak for 1-2 hours to get the Trichoderma into the water.

We have also started using the cornmeal water for other fungal diseases including Hypoxylon Canker, both Ganoderma, and Kretzschmaria (charcoal rot or burnt crust rot).  Dr. Percival mentioned in his 2017 talk that Trichoderma was also producing an antibiotic, so we have applied the drench to trees with Crown Gall.  So far, we have been pleased with the results and clients call asking for an annual re-treatment or ask for direction so they can mix their own.  I had a medical doctor laugh at us when we applied Trichoderma to two mature Sycamore on his ranch.  He called 6 weeks later to ask for mixing directions.   I plan to try some this summer on Cedar Elms at the Head Waters Reserve to see what it will do with BLS.

I understand this is not the kind of science we need.  Who is going to sponsor a study for something this simple that has no chance of being profitable on a large scale.  I write this not to say we have a cure for any disease.  SIR is real and it is working.  As pesticides become less effective, as they become banned for use, as they kill beneficial organisms and pollinators, we need alternatives.  That is why the research that is done is coming out of Europe and Great Britain where agrochemical use is so restricted.  They are also working with Salicylic Acid (active ingredient in aspirin) for SIR effects and several other products and organisms.

If you get a chance, play with Trichoderma and see what it will do for your disease control.   As Dr. John Ball teaches, all trees in an urban environment are stressed.  Trees have developed marvelous systems for combating disease.  We need to use or enhance these natural systems whenever we can.  Give Trichoderma and SIR a try and let us know failures and successes.

Recommended Small to Medium-sized Trees

Recommended small to medium sized trees, native or perform like native

  • Kidneywood (Eysenhardtia orthocarpa) 10 feet

    Mexican Buckeye

  • Mexican Buckeye (Ungnadia speciosa) 30 feet
  • Evergreen Sumac (Rhus virens) 12 feet
  • Rusty Blackhaw (Viburnum rufidulum) 20 feet
  • Carolina Buckthorn (Frangula caroliniana)  15-20 feet
  • Yaupon Holly (Ilex vomitoria)  25 feet
  • Possumhaw Holly (Ilex decidua)  15-30 feet
  • American Beautyberry, French Mulberry (Calicarpa Americana) 10 feet
  • Texas Persimmon (Diospyros texana) 20 feet
  • Crape Myrtle (many varieties, colors, bark pattern) 10-35 feet
  • Roughleaf Dogwood (Cornus drummondii)  15 feet
  • Texas Mt. Laurel (Calia secundiflora) formerly (Sophora secundiflora) 10-20 feet
  • Texas Redbud (Cercis Canadensis var. texensis) 10-20 feet
  • Dwarf Pomegranate (Punica granatum Nana) 10 feet
  • Anacacho Orchid Tree (Bauhinia lunarioides) 10-12 feet
  • Chihuahuan Orchid Tree (pata de vaca)   (Bauhinia llunapoides) 12 feet
  • Mexican Orchid Tree  (Bauhinia Mexicana) 10 feet
  • New Mexican Olive ( Forestiera pubescens subsp new Mexicana) 12 feet
  • American Smoke-tree (Cotinus obovatus) 35 feet
  • Texas Pistache (Pistacia texana) 15-30 feet
  • Mexican Plum (Prunus mixicana) 25 feet
  • Golden-ball Lead-tree (Leucaena retusa) 25 feet
  • Eve’s Necklace (Styphnolobium affine)  formerely (Sophora affinis) 25 feet
  • Flame-leaf Sumac (Rhus copallina) 25 feet
  • Bluewood Condalia (Condalia hookeri) 30 feet
  • Vitex or Lilac Chaste Tree (Vitex agnus-castus) 30 feet
  • All citrus and fruit trees.  Purchase from Fanick Nursery with their recommendations.
  • Texas Ebony (Ebenopsis ebano) 40 feet, thorns

A Simple Review – The Plant Cell

I am fascinated by the plant cell…

All life functions must occur within a cell.  This microscopic structure is filled with organelles and tunnels and performs manufacturing of everything needed for life on an unimaginable scale at speeds that cannot be comprehended.

Just how small?  You need to forget about inches.  Plant cells are 10 to 100 micrometers.  For the metric challenged, that’s 0.0004 to 0.004 inches.  They are 3 dimensional.  About 50 can fit on the period at the end of this sentence.  While this size might seem like a limiting factor, it is the perfect size for life.

Public Domain,

The plant cell is surrounded by a cell wall.   Woody plants also have an inner cell wall.  It is called a wall, but it looks more like lattice work.  Water, ions, and gas can easily move through this cellulose lattice to the cell membrane.  This can occur at a rate of 10 million molecules per second.

The cell membrane sits against the cell wall.  There are special proteins on the cell membrane that produce the cellulose and lignin lattice structures that form the cell wall(s).  The cell membrane is fluid and is the consistency of thick motor oil.  It is constantly moving and changing position.  It is a double phospholipid membrane.

The outer cell membrane is called the plasmalemma.  It is a semi-permeable membrane that only allows certain stuff to pass through.  Good stuff in, and good stuff and waste out.  Good stuff out like the exudates that are intended to feed mycorrhizae and beneficial bacteria.   Water and what is dissolved in water can easily pass through.  So can oxygen, carbon dioxide, and nitrous oxide.  Other molecules enter through special transport proteins and carbohydrates embedded in and going through the plasmalemma.

The plant cell membrane has tunnels called plasmodesmata and these tunnels are connected to all adjacent cells.  Every cell in the plant is connected by these tunnels. Once inside the plasmodesmata, water and other molecules of the right size can travel to every cell in the plant.  You could enter one of these tunnels in a root cell and eventually travel all the way to a leaf cell without ever leaving this tunnel system.  An individual plant cell can have from 1,000 to 100,000 of these tiny tunnels.

Aquaporins are proteins embedded in the plasmalemme.  They are so small they can only transport water one water molecule at a time. Aquaporins use no plant energy for this transport and rely on the cohesion property of water.  One at a time, water molecules move through an Aquaporin, 10,000 per second. Wonder what graduate student did the counting?

There are many other types of transport proteins embedded in the cell membrane.  Each allows specific molecules to enter or exit the cell.  A tremendous amount of the energy used by a cell is dedicated to producing these transport proteins.

Pump proteins use energy from sodium and potassium and hydrogen to move other molecules across the cell membrane.  To enter, a molecule must have a charge.  It must be an ion (with the exception of Boron).

The plant cell is very cautious about what it lets in.  Even with all these specific mechanisms for transport, sometimes something is available that is needed and it is too big or there are no specific transport proteins for it.  The cell membrane envelopes it (endocytosis) and moves it across.

Inside the cell membrane, the cell is filled with a liquid cytoplasm.  Within the cytoplasm are organelles.  Also floating in the cytoplasm are proteins and enzymes and amino acids.  It is about the consistency of a thick tomato soup.  Incredibly there are about 1,000 different proteins, maybe a total of 100,000 proteins at one time floating in this soup.  And that’s just in the space that is not occupied by organelles.

The organelle that produces energy from the sugars made by photosynthesis is called mitochondria.  It is surrounded by a double phospholipid membrane embedded with transport proteins.  There are thousands of mitochondria in most plant cells.  Inside, enzymes strip electrons from glucose molecules and use them to add phosphorus atoms to ADP to make ATP.  ATP is the energy source for functions within a cell.  Breaking the phosphate bond of ATP returns it to ADP and releases an electron that supplies that energy.  All life, no matter how small, requires energy.

Ribosomes are organelles that are the factories for protein synthesis.  Ribosomes are produced by the nucleus.  Some are free floating in the cytoplasm and some are attached to the rough endoplasmic reticulum.  The free floating ribosomes produce proteins used by the cell and those embedded in the rough endoplasmic reticulum produce proteins that are moved out of the cell for use in other parts of the plant.  Ribosomes do not have a membrane.

So, DNA in the nucleus replicates small sections of RNA which contain the blueprint for a protein.  Messenger RNA carries this message to a ribosome.  Transport RNA gathers the correct amino acids (there are 20) and delivers them to the ribosome.  The amino acids enter the ribosome, are assembled according to the directions of the RNA, ATP provides some energy, and out comes the requested protein.  The protein is then shipped to the Golgi apparatus, another organelle, for final processing.

The endoplasmic reticulum is a long membrane that is attached to the outer membrane surrounding the nucleus.  It has many folds and attaches to the cell membrane.  The part near the nucleus is called the rough endoplasmic reticulum due to embedded ribosomes.  Proteins are processed here with nucleotides that send the protein out of the cell to a specified destination.  Sugars can be added to the proteins making them into glycoproteins to be used for cellular functions and reactions.  Toxins in the cell are changed into benign substances for transport out of the cell.

The Golgi apparatus is attached to the endoplasmic reticulum.  The Golgi apparatus is surrounded by a membrane and it is the packaging and shipping center of the cell, the FedEx of the cell.  It is surrounded by tiny tubules that extend throughout the cell.  There are only about 5 to 8 Golgi apparatus in a cell and almost all molecules within a cell must pass through one of them.  Each one has a separate set of enzymes.  Molecules are finished, sorted, chemically tagged with a destination code, and then loaded into vesicles for final transport along the tubules.

Taking up the most room inside the cell is the vacuole, another organelle that is surrounded by a membrane embedded with transport proteins.  It maintains a pH of 7 in the cytoplasm.  It can merge with the cell membrane to purge waste.  Waste can also be recycled by Lysosomes and Peroxisomes.

Lysosomes digest proteins and break them into their component parts for recycling in the plant cell.  There are up to 100 in each plant cell.  They have a pH around 5.

Peroxisomes digest fats and lipids.  In seeds, they provide enzymes that start the conversion of stored fatty acids to sugars.  They help with the assimilation of nitrogen and the metabolism of hormones.

The nucleus is where the genome is stored along with instructions for synthesizing proteins.  It is surrounded by 2 phospholipid membranes.  The outer membrane becomes the rough endoplasmic reticulum.  The inner membrane of the nucleus (nuclear lamina) is a mesh network of fibrous proteins.  Inside is DNA, RNA and the nucleus has its own organelle, the nucleolus.  The nucleolus is the organelle that produces ribosomes.

How’s that for complex and small.  And we have not even mentioned chloroplasts.  There are typically 40-50 chloroplasts in each plant cell.  Each has a double membrane.  They contain chlorophyll.  In a leaf, there are about 500,000 chloroplasts per square millimeter.  Inside each chloroplast, thylakoids are stacked with attached chlorophyll molecules.

When light hits a chlorophyll molecule’s electrons, they jump into an outer orbit.  This increases their energy level causing electrons to flow (like electricity).  They flow through a special channel protein, ATPase.  This results in a phosphate being attached to ADP to make ATP, the energy source for biological systems.

The electrons then get a second dose of light and are picked up by NADP (I will mercifully not spell that one out).  The energy from ATP is used to form a sugar molecule.  Each chloroplast can create thousands of sugar molecules per second.  With 500,000 per square millimeter of leaf tissue, a plant can generate an awesome amount of sugar.

The outer cell wall and the plasma membrane are a barrier and regulator of what may enter and exit the cell.  Special membrane proteins allow water and nutrients to enter the cell while keeping unwanted stuff out.  The cytoplasm holds structures and organelles that perform functions using nutrients.  Mitocondria provide power for biological functions.  The nucleus is the command center containing DNA, RNA, and its own organelle.  Cells have transportation and communication infrastructure, protein synthesis areas, and even tunnels that connect every single cell within the plant.  All contained in a body so small that 50 can fit on the period at the end of this sentence. All cells come from other cells.

All functions necessary for life take place within each cell.

I am fascinated by the plant cell…


This article was based on Jeff Lowenfels’ Teaming With Nutrients, Chapter 1.

When A Tree Grows New Bark

The car struck the tree at more than 60 mph. The teenage driver was dead and his girlfriend was in intensive care. The car was wrapped around a tree and the car battery had gone thru a metal garage door about 25 feet from the tree. The 15 inch Cedar Elm was standing straight but had a large wound. A wrecker pulled the car from around the Elm and that doubled the size of the wound. Now we had a wound that involved 80% of the circumference of the tree and was 3 to 4 feet tall. Our client owned the tree and we got the call the next day. When they wait for the insurance appraisers, that call normally takes a week.

Our client asked what it would cost to remove the tree and was amazed when we told her we could save it and that the wound would be covered in a year. She was more surprised when we told her it would only cost 2 hours of labor and 50 gallons of fertilizer. Folks do not expect low costs, especially when the other guys insurance is paying for everything.

Elm as it looks today (2011)

Elm as it looks today (2011)

The client was skeptical, but I was confident in the outcome and she decided to let us repair the tree. Maybe my guarantee to remove the tree at no cost next year if she was not happy with the outcome had a little to do with her decision. I called our production manager and that afternoon he traced some ragged bark and tacked a piece of roofing felt over the wound. We use roofing felt because it is flexible, easy to cut and, unlike black plastic, holds up for the year we want the wound covered. A few days later the tree was fertilized. That’s it, very simple.During the year after the accident, the Elm did not show any signs of stress. Our client removed the roofing felt after about 11 months. The wound was about 90% covered with normal looking bark and with normal functioning cambium under that surface callus. Dr. Dirk Dujesiefken in his ISA PodCast October 2010 states that their studies show that not only do we get normal woody tissue, normal bark, and normal cambium; we also have no discoloration and no decay under the surface callus.

I did my first car damage repair in 1980 on an Arizona Ash. I was Allan Brook’s production manager, had my BS in Forestry and my MS in Arboriculture, had never heard of such a thing, and was pretty sure that Mr. Brook was touched. Back then we covered the wound with roofing felt and sealed the edges with roofing tar or mastic, very messy. I went back every two months, removed a corner of the felt, peeked in and could not believe what I saw. After a year, the Ash had 100% coverage of the wound.

I have since done this to about a dozen trees, mostly Live Oaks, one Pecan, one Red Oak, and have had similar results. The biggest problem is getting to the tree within 3 days, maybe 5 days of the wounding. Victims will wait on the insurance appraisers.

I have not tried this procedure on a limb. The BMP says it will work on a limb. Almost all of the limbs we see that are damaged by vehicles or equipment are too low and need to be removed for clearances. The one time I did have the right situation I did not think about the procedure and lost the opportunity to try it. When you only do something 12 times in 35 years it’s not the first thing to come to mind (I’m sure it has nothing to do with old age!).

Our BMP says you can use plastic or burlap to cover the wound. I like roofing felt because it is easy to work and form, it lasts a year in Texas heat, and it’s hard to see so people leave it alone. Anything that keeps the parenchyma cells moist will work. Painting the wound is not necessary and not recommended, but this procedure will work even if the wound has been painted. We paint the roofing felt to cover the roofing nails and to cover lines that are on the felt.

Take a look at the before and after pictures. This procedure works. Five years after the accident, the Elm is still looking good. One spot on top of one of the major roots did not cover and I am seeing some decay in that area that has me concerned. Give it a try the next time you are asked to be an EMT for a damaged tree and you need to perform Tree-a?ge.

David Vaughan
San Antonio, Texas

What You Should Know About Soils

soil(updated March, 2017)

Soil is more than sand, silt, and clay with some small amount of organic matter.  You may have 3 inches of clay over caliche, or 12 inches of blackland clay, or 5 feet of sand over hardpan. Whatever you have, soil is teaming with life.

Experts estimate that a tablespoon of forest soil contains 6 billion microorganisms consisting of 75,000 species of bacteria, 25,000 species of fungi, 1,000 species of protozoa, and 100 species of nematodes.  And that is not a typo; that is number of species.

James Urban in Up By Roots uses a cup of soil (that’s a handful for me) and has numbers in the billions;    200 billion bacteria, 100,000 meters of fungi (that’s about 60 miles!), 20 million protozoa, 100,000 nematodes, 50 micro arthropods.  That’s not much soil to contain such mind boggling numbers. The numbers are so large, so extreme; I do not think they register with most of us.  It’s hard to imagine how small you have to be to have 200 billion in a handful of soil.

Under good conditions bacteria have the ability to multiply or divide every 20 minutes.  They could quickly overwhelm the soil unless billions of them were consumed every hour.  A protozoa can consume 10,000 bacteria a day and there are 20 million protozoa in a handful of soil.  Nematodes eat bacteria, some protozoa, and a lot of fungi.  Arthropods eat all of the above. Fungi consume nematodes, decompose the bodies of whatever dies, decompose organic matter, and release nutrients from soil particles and rock.  Bacteria also decompose organic matter and release nutrients from soil and rock.  All are completely dependent upon carbon which can only be supplied by plants.

This is the soil food web.  The entire process protects nutrients from leaching out of the root zone of plants by securing nutrients within the bodies of microbes.  Plants and trees are very particular about the nutrients they absorb and prefer nutrients in a form that has been manipulated by microorganisms.  The nutrient needs to be consumed by a bacteria that is then consumed by a protozoa or nematode and then pooped out in the rhizosphere in ion form. The rhizosphere is a small zone of intense biological activity about 2mm wide (1/10th inch) around a root.  Only then is the nutrient in a form that the plant root can absorb.  So bacteria put out enzymes that release nutrients that they absorb. A protozoa consumes the bacteria, uses what it needs and releases the leftovers which have been converted into a form plants can use.  If the waste is released in the rhizosphere, the expanding root is able to pick it up thru diffusion.

In exchange, the plant provides carbon sugars it has produced during photosynthesis.  About 40% of what a tree produces in its leaves is leaked out thru roots to nourish the bacteria and fungi around those roots.  That is a lot of product being leaked, an indication of how much our trees depend upon the micro soil food web.  The bacteria depend upon their sugar daddy and crowd in on the expanding root like pigs at a feeding trough, forming a physical barrier that excludes bad bacteria.  When things are healthy, the bad guys do not have access to the root or to the sugars. When things are right, the good guys out compete the bad guys, limiting the numbers that could cause trouble.

Fungi can also form a physical barrier around a root, so thick that nematodes and other bad guys are excluded. Many of these fungi are mycorrhizae fungi that are attached to the root or have structures inside root cell outer walls.  The tree provides carbon sugars to the mycorrhizae in exchange for water and nutrients, especially phosphorus.  Fungal hyphae can be 1/60th the size of an expanding root and have the ability to get water and nutrients from very small pore spaces in the soil.  Mycorrhizae fungi are able to deposit water and nutrients directly into the plant root where the water and ions move through a cell membrane into root cells.

Fungi eat or consume nematodes.  Some form snares with their hyphae, put out a nematode attractant, and close the snare when a nematode enters the trap. They then grow a special structure that penetrates the sightless worm to consume the groceries.  Other fungi produce a poison that kills the microscopic worm when the toxin touches its mouth. Some use glue to glue trap the worm.

And then there are the arthropods (mites). They are the big guys in this micro world, eating fungi and nematodes and protozoa. And all these guys are pooping nutrients in forms that plants can use. Many of these waste products get picked up and consumed enough times in this soil food web to become fairly stable compounds which are how humates are formed.

Trees and plants are completely in charge of this system.  They have the ability to change the sugars they provide to stimulate certain bacteria or fungi according to their needs.  They change the sugars they produce by season, by temperature, and by moisture levels.  If they need iron, they produce a sugar to stimulate the fungus or bacteria that can provide that need.  Low on water and they stimulate the mycorrhizae fungi to bring in more water.

Bacteria could easily be washed away so they glue themselves to soil particles.  They use organic glues produced from the sugar compounds supplied by plants. These glues are similar to the ones produced by the bacteria in your mouth that cause morning mouth and tartar.  Clay particles tend to be rod shaped and bacteria can glue these end to end forming odd shaped structures that can resemble a snow flake.  This is the smallest soil aggregate and it protects the bacteria and provides space for the slow movement of air and water.  In sandy soils bacteria form cup like aggregates which hold water.

Fungi need to protect their reproductive structures from grazing arthropods, so they weave or glue several of these bacterial soil aggregates together and hide their fruiting structures inside. The glue they use is called glomalin and it is responsible for about 33% of the carbon found in soil when mycorrhizae fungi are present. This forms a larger soil aggregate, still too small to see with anything other than a high powered microscope.  Millions of these are formed within a handful of soil and they are an important, critical component of soil structure.  The movement of nematodes and arthropods create small passages that also provide for the slow movement of air and water.  These are the aggregates we destroy with compaction, plowing, tilling, and double spading our gardens.  Once these small aggregates are eliminated, water or air will not pass through.  If you want your soil to be healthy, you should not see it very often.  Keep your soil covered with plants and undisturbed.

Trees and their roots can get lazy.  When we provide nutrients to plants in forms they can use with very little biological activity, the tree will reduce the exudates it releases, which reduces the population of the good guys and can give the bad guys access to our plants.  It makes plants dependent upon chemical fertilization.  Fertilizers with high salt content (quick release and water soluble) can desiccate bacteria and fungi and can irritate worms causing them to leave the area.

We need to regard soil as a complex system of living organisms and seriously think about becoming microbe farmers, like the trees in a climax forest.  With the exception of pH, the physical properties of soil are not nearly as important to a gardener or arborist as the invisible living microbes occupying the soil. Your top priority in caring for soil should be to protect and preserve the soil food web.

This article was based on the incredible work of Dr. Seuss in his landmark soils manual, Horton Hears a Who with help from Up By Roots by James Urban, The Soil Will Save Us by Kristin Ohlson, Teaming With Microbes by Jeff Lowenfels and Wayne Lewis, the Certified Arborist Study Guide, Teaming With Nutrients by Jeff Lowenfels, and Teaming With Fungi by Jeff Lowenfels.

David M. Vaughan
Certified Arborist TX 0118
Member American Society of Consulting Arborists
Organic Certified, Texas Organic Research Center