Ball Moss and Mistletoe Removal

Ball moss and mistletoe are two common tree pests in Central Texas,

ball moss

ball moss

frequently removed when tree pruning.  Here is some info on what these plants are, how they are harmful and how they can be treated.

Ball moss is not really a moss, but an epiphyte or air plant, meaning it’s roots are exposed to the air.  It is in the bromeliad family, and so is related to pineapples, believe it or not.  While the majority of experts believe it is not harmful, because it is believed to receive its nutrition entirely through air and rain, some arborists including me believe that in large quantities ball moss definitely has a negative impact on trees.  This is due to its shading out buds and young leaves.  There is definitely a major impact when we have ice storms, as the greatly increased surface area causes much more breakage on limbs coated with ball moss.

There are really only two ways to deal with ball moss.  Manually remove it, or spray it with chemicals.  Manual removal is the far superior technique, as it can be extremely thorough and can address any pruning needs at the same time, while eliminating the side effects of chemical use.  However, it is far more expensive, usually more than five times the cost. Another problem with manual removal is that the average tree service’s unskilled climbers often remove too much foliage or damage a lot of the tree bark when removing ball moss.

Spraying is usually accomplished with one of three chemicals.  Baking soda is one of them, and while it sounds benign, its high salt content and pH can be harmful to soils.  It is also not nearly as effective as copper hydroxide.  This chemical can be harmful to young foliage and is toxic to aquatic life however.  A third salt, potassium bicarb, while extremely effective, is extremely expensive, and actually not labeled for this use.  Unfortunately, none of these chemicals will kill more than about 70% of the moss, usually killing only about half, and the moss remains on the tree for months or even years until it finally rots off.  With manual removal, it is gone instantly.

Mistletoe is undoubtedly a parasitic plant and harmful to trees.  Its root system (haustoria) is in the wood of the tree, drawing water and some nutrients from it.  It can also cause a weakness of the tree branch it is attached to.  In these ways, mistletoe causes significant problems for trees and should be removed annually.  There really is no spray option for mistletoe.  While there is a spray on the market, it only defoliates the parasite; it doesn’t actually eradicate it.  And it can wreak havoc on understory plants.  So manual removal is the only practical option here.  Unfortunately, complete removal is not possible once the mistletoe is severely entrenched in larger tree limbs.  Smaller limbs that are infected should be completely removed.

For more information about why you should choose Arbor Vitae Tree Care for these and other tree care needs, visit one of my web pages.  To set up a consultation call 512-301-8700.

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Tree Fertilizing

Red oak showing iron deficiency common in alkaline soils

Tree fertilization can be performed in numerous ways and goes by a number of names.  Sometimes called “deep root feeding”, this term is incorrect for a couple of reasons, and is a good clue that someone calling it that has a poor understanding of tree care.

Trees produce their own food, as you may recall from 6th grade biology, creating sugar through photosynthesis.  When we fertilize trees we are not giving them sugar but instead providing essential elements that they require to create various cell structures and perform various functions essential to survival.  These elements are often referred to as “nutrients”, which could explain how the term feeding came into use.  There are 17 of these elements (including carbon, hydrogen and oxygen), but I am only going to focus on a few.

If you were to buy a bag or bottle of fertilizer, you would see three numbers on it. This is referred to as the analysis, with the numbers representing nitrogen, phosphorus and  potassium (N-P-K) in that order.  These are the three so-called “macronutrients” that the tree uses in larger numbers than most of the other 17 and are most commonly deficient across a wide spectrum of soils, so these are the ones most commonly applied when fertilizing not just trees but most plants.  It is important to remember however, that these three may not be deficient in your soil.

For instance, in the Austin area, P and K are often “off the charts” in terms of how high an amount is present in our soils.  Adding too much of any element can be toxic, often by making the tree unable to take up other elements.  Phosphorus is a good example of that, and it can also be harmful to beneficial microbes.  This is why I often recommend that a soil analysis be done to see what elements, if any, are needed.  I emphasize “if any” for an important reason.  Many tree services promote fertilizing services that are totally unnecessaryencouraging customers to sign up for annual fertilization.   At Arbor Vitae Tree Care, trees are only fertilized when deficiency is known or strongly suspected.  Clients are never signed up for routine or annual fertilization.

Nitrogen is commonly deficient in Austin area soils, as it is in many places around the world.  How can this be, if our air is almost 80% nitrogen?  The short answer is because most trees cannot absorb nitrogen in its gaseous state (certain trees have bacteria in their roots that can).  And since nitrogen converts into a gas quite readily from the ground surface, and leaches out of the root zone with rainfall and irrigation, there is often little of it present in the root zone in a state in which trees can absorb it.

Add to that the fact that in most residential areas plant litter like leaves and lawn clippings are often removed on a regular basis.  This practice breaks the “nutrient cycle” and is one of the most detrimental things you can do to your trees.  This litter contains many essential elements and also adds vital structure to the soil.

Nitrogen deficiency often appears as an abnormal paleness or yellowing of the entire leaf, with this discoloration first appearing on the older (inner) leaves.  Often the leaf is undersize as well.

Another common deficiency in our area is iron (photo).  Curiously, this is not because iron is deficient in our soils, but because of our soil’s pH.    A soils’ pH is a measure of how acid or alkaline it is, and because of the great amount of limestone (calcium) in Austin soil’s our pH is often around 8, which is very high.  Just as an acidic (low pH) soil can make some elements unavailable in plants, so to can a high pH, and iron is one of the elements most commonly affected in this way. This also means that an iron deficiency may not be revealed by a soil analysis.  Foliar analysis is sometimes used in this case.

As I mentioned at the start of this blog, there are numerous ways to introduce elements into a tree’s system, from spreading it on the ground to injecting into the trunk, to spraying it on the leaves.  Both of those techniques have their place, but I’d say that place is limited, as they both have significant drawbacks as well.  If a tree service recommends one of those techniques, be wary, and find out what their justification is.

The technique I find best involves injecting a customized blend of elements and compounds with proven soil and microbe benefits below the surface.  But contrary to popular belief, most of a tree’s absorbing roots are fairly close to the surface.  If someone is recommending “deep root” fertilizing, meaning more than a foot deep, they are probably bypassing the vast majority of the tree’s root system, and the product you paid so much for is just polluting our aquifer.

That is another thing to consider when fertilizing.  If applied excessively, improperly or in the wrong form, the risk of polluting our aquifer is very high.  This is because of the fact that most of Austin is sitting on a giant block of limestone swiss cheese (called “karst”).  If you purchase a fertilization service based on price, you may be getting a poor quality fertilizer.  These are often high in salt (which can harm your trees in a drought or if over-applied) and/or are highly soluble, which means they leach into the aquifer faster and more completely than a higher quality one.  Always ask what kind of fertilizer a service is using.  A competent arborist will give you a thorough explanation.  The blend I use is specifically intended to be retained by the soil rather than leaching through it or vaporizing.

I’m posting this in the spring because people often ask what time of year to fertilize.  Research has indicated benefits to fertilizing in either spring or fall, and avoiding the hottest and coldest months.  That is my recommendation.  Depending on what species I am fertilizing and what the deficiency is, I will tailor the timing as needed.

The subject of tree fertilizing would take a book to thoroughly address.  These are just a few of the things a competent Certified Arborist would consider before proposing the service for you.  Call me today for a consultation.  512-301-8700.

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Tree Decay and Hazardous Trees

may 06 storm (39)

Remaining stub from fallen limb showing internal decay

As mentioned on my Pruning Tips page, tree safety is one of the two most important aspects of tree care.  And a critical component of tree safety is knowing how to assess potentially hazardous trees or limbs.  Being able to detect decay is a major part of that.

A few things to understand right off the top about this subject;  tree decay is caused by numerous species of fungi, and often the loss of wood strength they cause is not visible externally.  That means that no intelligent arborist is going to guarantee the safety of any tree or limb with 100% certainty.

A future post will discuss tree anatomy and physiology in greater detail, but for this subject it is important to know that the vast majority of a tree’s “business”, that is the transport of water and nutrients that keeps it alive, is occurring in the newest wood, that created in the most recent growing season, which is located immediately below the bark.  That is why a tree can be completely hollow and still look green and beautiful.  The inner wood (misleadingly called the “heartwood”) is largely inactive physiologically.

However, if this heartwood is missing, in either a trunk or an individual limb, quite a bit of strength loss can occur, increasing the probability of failure.  Sometimes this occurs with an external opening (frequently referred to as a “cavity”), which increases the risk of failure even more, but also making the defect much more noticeable.  Other times, as alluded to above, there is no external sign.  Although the tree or limb is likely more structurally sound in this case, it is also more likely to go unnoticed.

ganoderma thielmn (1)

decay fungus fruiting bodies or “conks”

Another sign of decay fungi is the fungus itself, visible when its fruiting body is present.  These are sometimes referred to as “conks” but most people know them more commonly as mushrooms.  And just like picking an apple off an apple tree doesn’t kill the apple tree, removing these conks isn’t going to kill the decay fungus living in a tree.  That is partly why there is no effective treatment for decay fungi. 

This is an important thing to keep in mind when hiring an arborist to deal with possible decay problems.  If they are telling you they have some kind of treatment, either physical or chemical, that can eradicate decay fungi, they are trying to sell you something that will not work.  That is not to say that there are not treatments for many other types of fungal problems.  There are.  Just not successful ones for decay fungi.

may 06 storm (1)

Live tree with full canopy falls from root rot


may 06 storm (3)

Close up of decayed roots on same tree

Dealing with decayed trees or limbs begins with an assessment of their severity.  This is usually accomplished visually, but much less frequently through an internal assessment.  A competent arborist can explain the options available.  One of the biggest factors in determining the risk level present is simply assessing what can happen if the tree fails.   For example, is it in the middle of a rarely used field, or is it over a playground?  This greatly affects whether one will decide to leave the tree or limb alone, remove it, or support it.

Sometimes support cables can be a reasonable option.  They can also be used to support limbs that have physical defects in them rather than actual decay, or to keep them from gradually getting closer to a building or walkway due to weight (the main header of my blog shows me installing a support cable for this purpose).

One technique that was common for years that was discredited a few decades ago by the research of Dr. Alex Shigo (see Pruning Tips page) is the idea of carving out these decayed areas and filling them with concrete.  This so-called cavity work was really something of an art form when done precisely, but Dr. Shigo’s research indicated that in the vast majority of cases, this work was either harmful (when healthy tissue was damaged and/or infected by the process) or just plain useless.

Trees are able to internally “compartmentalize” the decay and withstand the water often held by such cavities.  A competent arborist can fully explain Shigo’s theory of compartmentalization to you.  The biggest benefit to filling them is really just eliminating mosquitoes.  In other rare instances, the filling or a metal cap over a cavity can provide a surface for new tissue to move across as the tree covers the hole, but if live tissue is damaged when applying such a treatment, more harm than good has been done.

So the bottom line is that if you spot any of these types of irregularities, you need to consult with a competent arborist for an accurate assessment.  You certainly want to protect your family and property from failing trees.  You have a duty to protect others by taking reasonable precautions to prevent trees on your property from failing.  This is something a knowledgeable arborist can help you do, but it it important to understand that only you can decide what level of risk is acceptable, and no assessment of tree hazards is a guarantee against injury.

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Arborist of the Year – 2012

Guy LeBlanc is honored to have been named the 2012 Texas Arborist of the Year by the International Society of Arboriculture Texas chapter and the Texas A&M Forest Service.  It is awarded in part for his 35 years in the tree care business, and his volunteer efforts to increase the public’s awareness of proper tree care.

Guy LeBlanc (2nd from left) receives the 2012 Texas Arborist of the Year award.

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Tree Insect Problems 2012

The last two years have turned out to be some of the toughest of the last half-century on our central Texas trees.  Last year’s drought outright killed an unusually high number.  Ironically, many that have survived, especially pecans, are now breaking apart due to drought-weakened wood supporting (or more accurately, not supporting) excessively heavy branch tips and nut crops due to recent rains.  For every tree service I have spoken to, 2012 has been the year of dead tree and broken branch removal.

But now what’s really making the phone ring are calls about “tree sap” making every thing sticky.  These calls are mostly about pecan trees, but people with crepe myrtles and oaks are calling too.  But it is not tree sap that is making a sticky mess of everything.  It is a variety of insects.

Tree insect pests are very roughly divided into three categories; those that suck, those that chew, and those that bore.   The class of insects causing so many problems now (summer) are the suckers, particularly aphids.  They generally feed on the underside of the leaf and can be seen with the unaided eye (although accurate ID usually calls for magnification).  And the sticky stuff?  Well, to put it bluntly, it’s poop.

You see, aphids are kind of like many humans.  They love sugar and don’t know when to stop eating.  An aphid just inserts it’s sharp little drinking straw of a mouth-part into a nice, juicy leaf and keeps sucking long after the sugary tree sap is flowing out its other end.  So in a way, it is tree sap.  It’s just “processed”.

The one causing the most problems for pecans now is the black pecan aphid, which is common every year in Austin, but is in record numbers this year, probably in part due to the very mild winter and all the lush foliage caused by heavy spring and summer rains.

Many deciduous oaks I have looked at are having aphid problems also, including wooly aphid on post oaks, but others are having problems with another type of sucker – the lacebug.  Not to be confused with the lacewing, a beneficial insect, the lace bug is a common pest of  oaks and sycamores.

Other insects in the sucking family that often cause problems in Austin are spider mites, plant bugs and psyllids.  Many of these sucking insects have characteristic damage patterns.  The lace bugs and spider mites, for example, cause what is called stippling; a mottled fine spotting of the top surface of the leaf.  This is caused by the removal of the leaf’s chlorophyll.  The pecan aphid causes dark brown dead patches on pecan leaves.  Other aphids and pysillids cause a curling of the leaf margin or other distortion of the leaf.

Of course, what everyone wants to know it what to do about these little suckers.  The vast majority of the time I recommend doing nothing, especially if the infestation comes late in the growing season as it is this year.  These deciduous trees will be losing their leaves in a few more months, and have already done a large part of their work (photosynthesis or sugar production for the plant – but that’s another blog).  In fact some experts say that photosynthesis is greatly reduced in most American deciduous trees when temperatures are routinely hitting 100 degrees F.

Just like years in which we have heavy caterpillar damage (when there are no leaves left at all), a healthy tree will recuperate from this.  At least with sucking insect infestations, some leaf surface is retained.  Sucking insect damage does often cause premature leaf drop, but again, healthy trees will recover from this.

Another problem with aphid “honeydew”, as it is called, is that because it is so high in sugar it is a perfect substrate for mold. This frequently causes a secondary mold infestation which can turn leaves black, especially on crepe myrtles, and this can reduce photosynthesis further.

If your tree was not healthy before the infestation, or you can’t live with the mess, you may wish to treat the insects.  There are a variety of things that can work.  It is important to use the least toxic substance possible, not just for human safety purposes, but because you don’t want to kill the beneficial insects as well.  If you wipe out the bugs that eat the pests, like ladybugs and lacewings, it can lead to a cycle of dependency on pesticides.  Another irony of some high toxicity pesticides is that those used to control some sucking insects have been shown to cause an increase in populations of others, especially spider mites, which are a totally different class of bug (arachnid).  Low toxicity treatments often include insecticidal soaps.

Finally, I recommend bagging and disposing of fallen leaves from infected trees.  It won’t cure the problem, but it can reduce reinfestation, and can suppress certain fungal leaf diseases, which I am also seeing a lot of this year.  But if your trees are healthy, fallen leaves are a valuable part of the nutrient cycle and should be mulched and left under the tree.

If your tree has not been seen by an arborist in the last year or two you should see my contact page to arrange a consultation.

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Choosing an Arborist

Unless you were specifically looking for me, you probably came across this site while searching for tree trimming, pruning, arborist, or some other tag words, and along the way have seen or may see sites for dozens of so-called arborists.  My oh my, how ever does one choose?

There are lots of variables that can help you find a competent person to provide tree care for you, but I’ll start with the word “arborist”.  It may surprise you to know that unlike “doctor” or “lawyer”, there isn’t any sanctified definition of this title, or the use of it- anyone with a chainsaw and a ladder can call his or herself one.  So that can be a clue right there- anyone stating or implying that they are “licensed” by the state to perform tree care is, as politicians love to say, being disingenuous.

Yet there is such a thing as a Certified Arborist.  The certifying organization is the International Society of Arboriculture.  They have had a national certification program in place since around 1991.  In Texas, the first I.S.A. Certified Arborist exam was given in 1992.   I was among the small number who took and passed that test, and I have maintained my certification ever since.  Renewal requires acquiring only 30 CEU’s over a three year period;  I have totalled over 700.  I also teach many CEU classes.

It is important to remember that passing the Certified Arborist exam does not make one the be-all-end-all of tree knowledge.  It is a test of the most basic knowledge one needs for tree care, and the prerequisites for being able to take the exam could include having planted flowers for a living (not that anything is wrong with that).  So there are some very smart people with pretty much no tree care experience who have passed the exam, and a lot of not-so-smart ones with lots of experience doing tree care really poorly.  So don’t let this be your only qualifier.

It is also important to know that most tree services in Austin do not have Certified Arborists actually performing the work they sell.  Often a company has a Certified Arborist as its owner,  salesperson or foreman, and the people actually doing the work were digging ditches the month before (not that anything is wrong with that).  You’re better off hiring a company in which Certified Arborists actually do the work, like mine.   And don’t be confused by the Certified Tree Worker designation (which I also have).  This certification  focuses more on basic climbing skills, not arboricultural knowledge.  While it is admirable for a company to certify its employees, it is by no means an assurance that the consumer will receive quality work.

It’s important to make sure that persons working on your property have an adequate amount of quality experience to back up their certification.  I recommend a minimum of 20 years for the owner or manager of your account and 7 years for those actually doing the work.  Yes, there are many with less experience that are quite competent, but the chances of getting an incompetent one (or worse) are higher with less experience.  However, there are also unfortunately many with more experience who are incompetent or even outright dishonest.

Insurance is another factor to consider.  All competent tree services in Austin carry appropriate insurance.  This means general liability insurance, personal injury insurance for owners and workers compensation for employees.  It may surprise you to know that none of these are required by law in the state of Texas.  Just to be clear, remember that having these insurances is not a guarantee of quality work.

But any company that does carry insurance will be happy to show you proof.  Just remember, you should verify that the policy is in force.  We had a case in Austin some years ago where the city hired a tree company that actually provided a completely bogus insurance certificate to the city, which the city never verified until after the work was done.  Despite this and the fact that the work did not meet industry standards, the company was still paid.  Your tax dollars at work…

Be especially wary of memberships.   My personal experience is that the more prominently a company advertises memberships,  in the Better Business Bureau for example, the less likely they are to be a quality operation.  The BBB has absolutely no enforcement power, and has little incentive to punish businesses who pay a fee to be members.  Likewise, memberships in tree associations like I.S.A. or T.C.I.A., without accompanying certifications or accreditation, mean nothing more than that someone paid an annual fee to use the group’s logo.  I have seen several tree companies in Austin over the years advertise membership in organizations that don’t even exist!

Finally, check the arborist’s work.  You can become familiar with what proper tree care is by reading about pruning on my website, and ask for and verify references.  Obviously, a company isn’t going to tell you about people who have been dissatisfied with their work, and internet referral sites are laden with misinformation (both pro and con), but if you take the time to become familiar with what a properly pruned tree should look like (it’s not rocket science), you can look at a few dozen trees and tell whether they have been pruned well or not.

Or just make it easy on yourself.  Hire Guy LeBlanc!


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Tree care for drought stressed trees

Last year’s record heat and drought compounded the severe impact that the 2009 drought had on trees in Austin, Texas.  In 2009 we saw record levels of dead and declining trees due to drought.  The heavy rains that occurred that fall and into 2010 were not enough to save many of the trees that initially survived.

severe dieback caused by drought

The same thing is happening now.  The heavy rains of this winter were not enough to save many of the trees that survived through 2011’s drought.  Now that the late-blooming species are in leaf, what is dead is apparent, and the phones at tree care services around town are really ringing.

My business is about tree care, not about being a “tree mortician”.   I have focused my 30-plus year career on maintaining trees and advising property owners on what they can do to preserve their trees.  This means pruning, cabling, fertilizing, and other tree care techniques.  I can certainly perform difficult removals, but they are not a satisfying thing for a highly experienced Certified Arborist.

So, what can one do for a drought stressed tree?  Well, the short answer is, unfortunately not much.  If there is substantial dieback, nothing is going to bring those dead limbs back to life.  Now that almost every live tree in Austin is in leaf, if it doesn’t have leaves, it’s very likely dead.  Once you know for certain that a large limb is dead, it should be removed quickly.  This is  for safety purposes.  Some species shed their dead branches much more quickly than others.  Pecan for instance can shed large dead limbs within a year, whereas live oak will often hang on to them for many years.  Dead limbs really aren’t a health issue for trees in the short term (less than a year).

Some tree services recommend fertilization for trees affected by drought.  Although fertilizing has its place, I do not automatically recommend this.  In fact, fertilizing can be harmful to a tree in a severely stressed condition.   Fertilization should only be used when there is a known nutrient deficiency.  This is something I always assess before considering the addition of nutrients.

The best approach to trees stressed by drought is to maintain proper irrigation levels and improve soil quality.  Soil improvement is largely done through the addition of organic materials to existing soils, but more aggressive mechanical means (such as an air spade) are sometimes employed for extremely poor soils.  As with fertilizing, there are right ways and wrong ways to improve soils.

Proper irrigation can be achieved for trees even under most stages of city water restrictions.  I generally recommend a thorough soaking about once a week during the hottest months.  How much time and water that will take will depend on your specific irrigation system, water pressure and soil type.  A heavy soak once a week is far preferable to multiple short waterings per week.  If you have a thick turf like St. Augustine grass, you may not even get much water through it and to the tree roots if you are doing short waterings, so in this situation your tree could still suffer drought stress even if you were watering every other day.  I can discuss the specifics of how to best achieve these things on your property during a consultation.

Another big problem that trees stressed by drought often experience is borer insect infestation.  Although some aggressive species of borers can attack (and kill) healthy trees, most are opportunistic, and are more likely to attack stressed trees, and some species are more susceptible than others.  While chemical treatment of these insects is possible and sometimes necessary, often the infestation is only noticed after the insect has already damaged the tree and is no longer present.  Correcting the stress factor is usually the best approach.

If you have trees that are in need of tree care, you will get the best results from a tree service in which the treatment is personally provided by an owner/operator who is an I.S.A. Certified Arborist with at least 15 years of local experience such as mine.  I have owned and operated Arbor Vitae Tree Care for 29 years.

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Spring is here! (Almost)

Guy LeBlanc

Warm weather will soon be returning to central Texas, which means folks here will soon be thinking about pruning their trees and other aspects of tree care.  A common question that comes up now is, “What about oak wilt?”  For years, it has been recommended by government agencies to avoid pruning oaks in the spring because of a perceived increase in the risk of getting oak wilt.  What is the reality of pruning oaks while minimizing the risk of this deadly fungus?

About a year ago, I chaired a group of arborists from the Texas chapter of the International Society of Arboriculture, the Texas Forest Service, and Texas AgriLife Extension Service which clarified the existing guidelines.  This was to explain to the public that certain kinds of pruning can be done year-round on oaks.  This would include removing dead branches, and branches at risk of being hit by vehicles over streets, and those rubbing against buildings or other branches within the canopy.  For details on this, see my oak wilt page.  You can also see a Central Texas Gardener video of me explaining oak pruning and oak wilt on YouTubeTo read the statement in its entirety, do a web search for “pruning guidelines for prevention of oak wilt in Texas”  and “Guy LeBlanc”.

oak wilt symptoms

Oak wilt has been in the news locally for so long (in Austin it almost created hysteria in the early 80’s) that I sometimes forget that most homeowners don’t really know much about it.  In brief, it is caused by a fungus very closely related to the Dutch Elm disease fungus which many folks from northern U.S. are all too familiar with.  It only affects oaks (and tanoaks).  The disease spreads in two primary ways.  The majority of the spread of the disease (95% of it according to one researcher) occurs underground due to the propensity of live oaks to form grafts (actual vascular connections) between the roots of different trees.  Live oaks also occur in groups called motts, which means that all of the trees in the group have formed from root sprouts.  Motts are also therefore interconnected and the disease spreads quite readily through them.

The disease can also spread above ground, creating new infection centers.  This occurs when vectors (in this case a beetle called the nitidulid is most likely the culprit) visit the fungal spore patches (called mats) on infected trees and then carry those spores to fresh open wounds on healthy trees.  In Texas these mats only form on red oaks, never on live oaks, so it is important to remove dead red oaks immediately- in fact in Austin, there is an ordinance requiring any property owner to do so.

It is believed that the nitidulid is attracted to both the odor of the mats, which have a fruity-licious smell, and the odor of fresh sap from new wounds.  The highest levels of this insect population and the creation of fungal mats coincide only when weather conditions are just right, which is usually in the spring.  This is why government agencies have recommended avoiding pruning in the spring.

However, we also know that very often in spring the weather conditions are not conducive to the development of the fungal spores (too hot and/or dry).  No spores = no above ground spread.  Or it can be too cold for the insects to be active (last year it was in the 20’s for 3 days at the end of Feb).  We also know that painting wounds provides a nearly total barrier against spore invasion.  There is no published scientific study in which painted wounds contracted oak wilt (one study in 2007 seemed to contradict this, but it was found that the trees were becoming infected underground).  We also know that dead tissue cannot be an invasion point for the spores, so removing completely dead branches never exposes a tree to oak wilt; technically, dead tissue doesn’t even have to be painted, however, I usually paint it just in case some live tissue is present on part of the wound face.

The bottom line is that while oak wilt is often fatal, the actual risk of contracting it through open wounds, even in the spring, is minimal.  If it wasn’t we probably wouldn’t have any oaks left, as wind, hail and animals such as squirrels and birds cause extensive wounding, often in the spring.  And this risk can be actually be reduced if the pruning is done by a competent professional – which is of course the only type of person you would ever let touch your trees!


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