Friday, July 22, 2016

Webinar on mosquito control Monday

Drs. Grayson Brown (top) and
Nicky Gallagher are featured
speakers at next week's Webinar.
Just a short post today about a webinar on mosquito control for PMPs on Monday, July 25.  It's sponsored by PCT magazine and will be held at 1 pm CDT (that's Texas time).  Free signup is available here.  Speakers are Drs. Nicky Gallagher with Syngenta, and Grayson Brown with the University of Kentucky, both excellent speakers and knowledgable in mosquito control technology.

My reason for plugging this particular webinar is its timeliness, in combination with the surprising growth of the mosquito control portion of the pest control industry over the past couple of years.  I was shocked to learn at this spring's National Conference on Urban Entomology that mosquitoes are now big player Orkin's #1 annual residential service offering.  And I was amazed to hear that Arrow Exterminating's mosquito annual revenue went from $39,000 in 2004 to $6.5 million in 2015,with mosquito control customers among their most loyal customers.

So if you service residential accounts and are not yet providing mosquito control services, you might want to check out this offering. All you need is a computer and connection to the Internet. What could be an easier way to grow your business?

Thursday, July 14, 2016

West Nile virus risk high in north Texas

Residual insecticides applied via backpack mist blower
sprayer can provide 3-4 weeks of mosquito control  during
times of peak mosquito activity.
July and August are typically the months of highest risk from west Nile virus, and true to form the past few weeks Dallas and Tarrant counties have seen a major increase in not only mosquitoes themselves, but infections within the mosquitoes.

After the major outbreak of WNV in 2012 in north Texas, some health officials made a decision to use something called the Vector Index (VI) as a form of threshold to ramp up mosquito control efforts.  Based on when human cases started to soar in 2012, and on suggestion from the CDC, a VI of 0.5 was determined to be a good threshold to consider going from ground based spray efforts to aerial spraying.

Two weeks ago the VI exceeded that threshold in both Dallas and Tarrant counties.  Both counties publish very interesting reports, available to the public, that include graphs to show  the latest mosquito counts and VI numbers.  To see the trends in Dallas and Fort Worth areas, check out the graphs below.  In the first graph, the Vector Index is the heavy red line.  Last week it exceeded the 0.50 threshold, although there was a drop this week. Note also the numbers of mosquitoes this summer (red bars) compared to average trap catches in 2012 (for the past four weeks, higher than 2012 averages shown by the blue bars). In Tarrant County (Fort Worth and surrounding communities) the VI (green line with triangle points) was likewise up last week, over 0.60 (new data is not yet published).  Note that the most recent 1-2 data points are preliminary estimates and may change as all the data is calculated.

These data are why there is discussion about aerial spraying this week.  In 2012 the number of human cases of WNV in Dallas county reached almost 400, and there were 19 deaths attributed to WNV. Serious business. Last week DCHHS issued a health advisory to the public, and this week the Dallas County commissioners voted to authorize the health department to prepare for possible aerial spray operations should conditions warrant.  

Where does all this leave the PMP who provides residential mosquito control service?  Municipal mosquito spraying actually complements, rather than replaces, mosquito control work on the ground done by professionals.  Aerial spraying generally provides better coverage of the tree canopy where WNV carrying mosquitoes (Culex quinquefasciatus in north Texas) live and mostly feed. Municipal truck mounted ULV sprays provide some control of lower level mosquitoes (Aedes mosquitoes that potentially transmit Zika and dengue fever, among other diseases), but they typically do not provide high level control in backyards or areas protected from spray coverage.  In that sense, the best control of Aedes mosquitoes is accomplished by your boots on the ground, looking for and treating or eliminating mosquito breeding sites, treating doorways, and treating shrubbery and other mosquito resting sites that are difficult to reach from the street.

As you and your technicians visit mosquito control customers this summer, keep in mind that you carry some of the most effective tools in the war against mosquitoes.  This summer, with Zika fears and WNV threats, what you do is more important than ever.

New Zika Resources for the Public

Hiring a professional is one way that the public
can help reduce mosquito biting risk around the home.
I was asked a few weeks ago if the collective "we" (meaning the whole state of Texas) were going to be ready for Zika.  My answer was a cautious, "I think so".  If we're not, it at least it won't be for lack of trying.

Zika is a much different disease than West Nile virus. It has different vectors, mosquitoes that prefer to feed on humans over any other animal (unlike WNV mosquitoes, which mostly feed on birds).  It is also very difficult to detect in wild mosquito populations.  The mosquitoes are more difficult to control with spray trucks, so responding to local cases is going to depend more on public cooperation.

Unlike WNV, Zika is virtually undetectable in the blood supply, as there is no approved way to screen newly donated blood to see whether it has the Zika virus in it. If Zika does make it into the country, it will also potentially affects more people.  Any family with members of childbearing age will need to be on high alert. The CDC recently released its response plan for Zika.  It's assumptions are sobering:
  • Travel-associated and sexually-transmitted cases will continue to occur and are likely to increase. (we just don't know how much!)
  • Local transmission (spread) of Zika virus in US territories and affiliated Pacific Island countries is ongoing.
  • Neither vaccines nor proven clinical treatments are expected to be available to treat or prevent Zika virus infections before local transmission begins nationwide.
  • The ability for mosquito control efforts to reduce infection risks may be limited, as has been the case with similar viruses, such as dengue and chikungunya.
The entomology department, and especially my colleague Extension entomologist Dr. Sonja Swiger, has been busy in recent weeks trying to figure out how to best arm everyone with the best information on how to prepare for the "Summer of Zika".

As part of the effort, some new fact sheets from Texas A&M AgriLife Extension are now available to answer some of the more common Zika questions. These may be useful for your customers who are worried about mosquitoes and how to protect themselves.  The DIY fact sheet talks about the different consumer-oriented treatment options, including hiring a professional.

Wednesday, June 29, 2016

The Exam Experience

It's been a long time since I've had to take an exam that meant anything. This morning, however, as I sat waiting to be processed to take my pesticide applicator's exam I felt a familiar, almost forgotten feeling. Test anxiety. Can I do this? Sweaty palms. What if I don't pass?

After all, I worry, I've been doing pest control and pesticide application for more years than I care to count. If I flub the exam, my research technician, who is taking the exam today too, will know. How embarrassing would that be? I'm supposed to know this stuff. I teach CEU classes for goodness sake.

So why after 27 years as an Extension specialist am I taking my applicator's exam? Well truth is that I did have a TDA non-commercial applicator's license for most of these years; but several years ago, amidst the busy-ness of life, I let my license expire. Then I discovered that it was kind of nice not having a license.  I go to plenty of CEU classes every year, so the education requirement wasn't the problem. It was just the minor but annoying process of keeping track of certificates, and sending in renewal forms (and money) every year. Also, my job doesn't really require that I maintain a license.  When doing research, all the compounds I've worked with recently are already registered, and so don't need a Research and Demonstration license, which TDA requires for researchers working with unregistered (numbered) compounds. When I do put out insecticides for trials, I have worked with other licensed applicators, so it didn't seem necessary to retest and re-establish my license (in Texas, folks can work under the supervision of non-commercial certified applicators).

So why go through the trouble of re-upping now? I guess it felt like the right thing to do. I don't like relying on other people for my licensing credentials. And it didn't seem right for me to be an instructor of pesticide applicators and not have a license myself. And the part of me wanted to remember what it was like to go through the study manuals and take the test like a raw recruit.

So this morning I sat in the sixth floor, PSI Services exam office of the Empire Central Building off of Stemmon's Freeway in Dallas. Even though the employees there were very nice, a kind of static anxiety hovered over the room and the testing center.  PSI has provided testing services for TDA since June 2014, and serves other industries as well.  The nervous young man next to me was sitting for his electrician journeyman's license. The test takers I saw were not a talkative bunch.  Sort of like sprinters at the Olympics, focused inward, centered... thinking "help me, God."

So for me the anticipation for me was much worse than the test. The test itself would be challenging without study or good familiarity with pesticides and the law.  It's definitely not a "no-brainer". But once the clock starts ticking and the questions start flashing I knew I could do this. I was signed up for three exams: General Standards, Landscape Maintenance, and Demonstration and Research.

The testing room was silent with a half dozen test takers sitting quietly, focused on their screens.  I found the quiet relaxing, but also noticed that the testing center provides ear plugs for those who want them.  I guess they are needed by some for our protection against "sighers" or "groaners" in the room.  Everything, by the way, is under video surveillance--so security is high.

If you haven't taken a "final" in awhile, and the thought of a test scares you, you're not alone.  I think the longer it's been since high school or college, the scarier the thought of sitting for an exam. This is normal, especially for us adults who have a lot of pride on the line. So here is my personal set of advice for pesticide exam test takers:
  • Relax.  If you've studied, you've retained a lot more stuff than you probably realize.  It's all in there; you just have to relax and let it flow.
  • Read the instruction screen explaining all the available buttons.  There is some interesting stuff there that can help you be a better test taker. 
  • Take the test one question at a time.  If you come to a question you're not sure about, the PSI test allows you to mark it.  Put the answer you think is right, then tag the question with the Mark button.  When you get to the end of the test, you can use the GO TO button to go back and view all the questions that you've marked.  It's a nice testing feature, and it's also amazing how those questions sometimes clarify themselves after you've had a few minutes to reflect and think about something else.
  • Read all the choices. Carefully.  Eliminate the obviously wrong ones (called "distractors" in test writing jargon), and focus on the remaining choices.  The tests, by the way, are all multiple choice with only 3-4 choices.
         BTW, another nice feature of the exam is that you can Comment on questions.  If you think a question is poorly worded or unclear, hit the comment button and explain why you think the question isn't fair or how it could be improved.  As you write, you may actually develop a clearer idea of what the best answer is.  I did this on several questions.  I didn't know if anyone would actually read my comments, but at least I felt a lot better getting it off my chest.
  • Don't be surprised to see math problems on the exams.  If math is not your strong suite, be sure to work and rework the problems in the AgriLife Pesticide Applicator License Exam Study Materials ahead of time.  Learn the formula "Gal/Min=((Gal/Acre) x Speed x nozzle width)/5940".  And learn how to convert milliliters and fluid ounces to gallons, and how to estimate square feet and convert to acres. Trust me, you'll need this.  The study materials I would say are essential.  In my testing center the staff did not allow writing tools (I guess so you can't write down questions), though they said we could have scratch paper if requested...???  
  • When you get to the end of the test hit GO TO all your marked questions.  Review them, choose your final answer, and Unmark them one by one.  If you have time, GO TO all test questions.  Quickly scan through all the question and reassure yourself you did a decent job. 
  • Don't leave any question unanswered. If you do, you will get the question wrong.  If you have to guess at least you've got a one-in-three chance or better of getting the answer right. At the top of the test screen it will tell you how many questions are unanswered.  Check it to make sure you didn't forget to answer a question.
  • Once you finish your test, you'll fill out a short feedback form and then receive your results on the screen.  No waiting for days or weeks to find out how you did.  Passing score is 70%, an achievable score for most people who study. The software also shows you how you performed on the various kinds of questions (calibration, legal, pests, etc.), but this will be the only time you see that data, so look at it closely and see where you went wrong and right (especially if you didn't pass, this will tell you what to study).  As I left the Center I was given a printout showing my final score for the three tests I took (passed them all!), but this sheet did not show the score breakdown.
I communicated with Allison Cuellar of TDA about the Commenting feature of the exams.  She said that staff at TDA do have access to the comments, but most of the comments they see are the ones sent via email directly to their offices. She seemed genuinely interested in feedback about the testing process.  So if you feel moved to provide positive or constructive feedback about your exam experience, contact Allison Cuellar (on the Structural Pest Control Service side) or Perry Cervantes (on the Ag side).

If you or someone in your company is preparing for the exam, being a little nervous is normal (as I was reminded this morning). But for most of us the anticipation is worse than the event. As for me, I had so much fun this morning, I'm thinking that maybe I need to go next for the Structural Pest Control non-commercial applicators license. I wonder if there's a loyal customer discount?

Wednesday, June 1, 2016

Correction to LEED reporting

I thought I had vetted my notes on the NCUE meeting last week, but was corrected this weekend on a few critical points by my friend, Dr. Chris Geiger, with the City and County of San Francisco (CSF). Chris is the most knowledgeable entomologist I know when it comes to LEED credit language and IPM, and has been integral to the pesticide hazard ranking system used by CSF.

My mistake in reporting had more to do with the talk by Tim Husen on PMP frustrations with LEED. At least some of the issues Dr. Husen and others in the past (including myself) have had with LEED pesticide language have since been corrected by the U.S. Green Building Council, keepers of LEED certification.

Dr. Geiger pointed out that there was never any official San Francisco Tier III list of pesticides. Several years ago there was a temporary listing of pesticides put up by the City, "but it was not at all exhaustive and went quickly out of date."  Unfortunately the list lives on in older web pages, and some governments and architects still refer to the Tier III list as if it were the universally accepted standard of P.C. (pesticide correctness).

Instead, the CSF maintains a series of criteria for determining hazard tier of pesticides.  Under LEED, some pesticides that are classified as least-toxic (low risk, Tier III) under these criteria are exempt from resident notification requirements in the LEED-for Existing Buildings Operations and Maintenance.  There is no longer any list of pesticides, since registered products change so quickly; however the Pesticide Research Institute compares pesticides to these criteria in the PestSmart app I mentioned.

So apologies to Dr. Geiger and CSF for my misunderstanding, and thanks for the polite redirect. My notes, and last week's blog post have been corrected.  To see the LEED IPM credit language for IPM in Existing buildings, click here.

Friday, May 27, 2016

Highlights of NCUE

Albuquerque, NM was a beautiful (and tasty)
location for this year's NCUE meeting.
One of the first professional meetings I attended as a newly minted PhD entomologist was the National Conference of Urban Entomology. Held that year in College Park, Maryland, the meeting was a revelation.  Finally, I thought to myself, a gathering of people who understand what I do for a living--like a Cheers bar for entomologists!

We've all been to parties and been asked what we do for a living. Answer that you're "an entomologist who specializes in structural insect pests", and if you're lucky you'll get a wan smile. Rarely does anyone get it. Not so at the National Conference of Urban Entomology. The NCUE is a gathering of very friendly, slightly nerdy, science-oriented people who love to talk about urban insects and pest control.  No one in this group needs bother with common names when discussing Periplaneta americana, or Coptotermes formosanus. Talks like "Gut bacteria mediate aggregation in the German cockroach" are guaranteed to draw a crowd.

This year's NCUE meeting was held in Albuquerque, NM, and it did not disappoint.  Besides a short, but packed agenda of buggy stuff, Albuquerque was a wonderful place to meet.  Not a whiff of Breaking Bad drug labs, but lots of clear skies, mountain and desert views, and great New Mexican cuisine. (Oh, and The Donald was even in town one night!)

To give you an idea about what all of us bug scientists talked about in the sessions and hallways this week, here are some of my notes to self:
  • Pest exclusion was the dominant topic for one session and was revisited throughout the meeting.  Imagine if homes and offices could be designed to keep pests out, or at least make them uncomfortable.  Dr. Jody Gangloff-Kaufman from the New York State IPM Program talked about two relatively new working groups dedicated to promoting better building standards to resist pests.  They call their project SCOPE (Scientific Coalition of Pest Exclusion), and the two groups focus on residential and commercial buildings, respectively.  The group has been meeting for approximately 2 years and has about 120 members.  Goals are to assemble a database of literature that supports pest exclusion (PE) concepts, and to provide checklists for builders and architects to promote better PE. A bit of controversy arose when a session speaker suggested that perhaps the typical pest control business model would not willingly embrace pest-resistant buildings. A PMP participant objected saying that offering pest proofing was an important part of their business model and how their company remained competitive.
  • Dr. Chris Geiger, with the City of San Francisco, spoke about how IPM and PE principles have influenced the LEED (Leadership in Energy and Environmental Design) program. LEED remains one of the most influential and successful certification programs ever, contributing $80.6 billion to GDP between 2011-2014 and changing the way architects design modern buildings. Dr. Geiger noted that 59% of LEED-for-existing-buildings applications take advantage of points for having an IPM program in place.
         Although LEED recognizes the importance of IPM to environmentally sound construction and maintenance of buildings, it has not provided strong leadership on pest exclusion. Consequently, in 2013 Geiger led a group to produce a guidance document for architects and builders to provide specific examples of how to make buildings more pest resistant.  These guidelines are being put to work in some major public housing renovations in San Francisco, and have been offered to builders as a standard to reference when trying to achieve IPM points in LEED projects.
         Dr. Geiger hopes to update these guidelines this year, and is actively seeking experts in pest control, engineering, entomology, and architecture to be a part of the process.  If you are interested in joining his group, go to this web form to add yourself to the list of participants.
  • Dr. Tim Husen with Rollins Corporation suggested that PMPs needing fast access to a listing of low toxicity products acceptable to LEED certifiers can use a mobile phone app called PestSmart, available through the Pesticide Research Institute. I found and downloaded this free app quickly on the App Store for my iPhone.  The listing is based on criteria used by the City of San Francisco in their (now extinct) Tier III list of low toxicity pesticides.  This famed list is no longer supported or updated by the City of SF, but is still sometimes referenced by architects, especially under the now dated, V3 (2009) LEED credits.  Keep in mind that the PestSmart app provides an assessment of likely toxicity, but does not take into account risk of exposure, an important component of hazard (toxicity X exposure = hazard).  
  • Famed "rodentologist," Dr. Bobby Corrigan, also spoke on rat exclusion, and provided a case history from the National Park Service's African Burial Ground Monument.  A highly sensitive, historically significant site in New York City, the property was heavily rodent infested prior to Corrigan's consultation.  Xcluder Geo Mesh was installed under sod at the site, and burrows were gassed with dry ice (2 lbs per burrow system) to successfully rid the property of these "diabolically clever" pests, as Corrigan described them. Though initially more expensive, Corrigan believes the use of CO2 and advanced mesh barriers like this could be very useful for eradicating rodents from sensitive locations.
  • Not surprisingly, mosquitoes were a hot topic of discussion this year. PMPs are beginning to shift their company business models to include mosquito control. Orkin's Dr. Ron Harrison noted that mosquitoes are his company's number 1 annual service offering. Rick Bell, with Arrow Exterminating, reported that his company's mosquito revenue has gone from $39,000 in 2004 to $6.5 million in 2015, all with little reliance on automated backyard mosquito misting systems.  He noted that Arrow's mosquito control customers are among their most loyal, with a 92% annual retention rate. 
  • Dr. Joe Barile of Bayer Environmental Science cautioned the industry about how mosquito control is marketed. He recommended use of the term "nuisance abatement" rather than any language that implied disease elimination or protection from mosquito borne disease.
  • Dr. Grayson Brown from the University of Kentucky summarized some of the latest promising technologies for residential mosquito control. He reported that the Innovative Vector Control Consortium (IVCC), a group founded over 10 years ago to seek solutions to mosquito borne disease, is currently evaluating 9 new classes of active ingredients for vector control. If even a few of these insecticides prove safe and effective, it could revolutionize adult mosquito control. He also noted that essential oils are also receiving more study as insecticides, repellents and excitatory agents to enhance the effectiveness of other products.
  • Although it appears that most pest control companies rely largely on barrier sprays as a core of their mosquito control programs, pollinator and beneficial insect concerns are an issue. Consequently, there is much interest in alternatives to backyard sprays for mosquito control. Among the promising alternatives, according to Brown, are autocidal gravid oviposition (AGO) traps.  These are artificial breeding sites for Aedes mosquitoes which trap, kill, contaminate or sterilize any female mosquito lured in to lay eggs.  In one study in Puerto Rico, 3-4 large AGO sticky traps per yard were sufficient to reduce Aedes mosquito populations 53-70% and prevented mosquito outbreaks following rain in 81% of homes. 
  • Pyriproxyfen, the insect growth regulator in Archer® and Nygard® insecticides, is also being tested as an active ingredient in some autocidal traps.  Research suggests that besides killing their mosquito offspring before they emerge from treated water or cups, pyriproxyfen residues in these traps transfer via the mosquito herself to other breeding sites through a process called auto-dissemination. This is one of the coolest and most selective mosquito controls I've heard of.  If proven in the field, a PMP or homeowner, could put a few gravid traps out in the yard for minimal cost and get season long mosquito suppression with no risk to bees, butterflies or other beneficial insects.  In combination with sprays and other control methods, it might be possible to achieve a high level of control and reclaim mosquito infested backyards with minimal harm to good bugs. Currently few lethal ovitraps are commercially available; but watch for new products to enter the market soon.
  • No gathering of urban entomologists would be complete without a few papers on bed bugs. Though the number of bed bug papers was down this year, those presented were oriented towards the practical.  Three papers came from Virginia Tech.  Dr. Dini Miller presented on bed bug vacuums. She found that all the battery powered vacuums she tested (several Black and Decker, and Dyson models) were surprisingly effective at removing adults, nymphs, exuviae and eggs. Besides offering a cleaner and more allergen free environment, it is notable that vacuums remove the exuvia (cast skins) of bed bugs.  This is important for control, she noted, as cast skins may be used by bed bug nymphs as a refuge from sprays.  She also recommended using disposable, knee high, nylon stockings over the mouth of your vacuum (which she colorfully called "condoms for your vacuum") to isolate your catches and reduce the risk of bringing bed bugs back to the office.
  • Katlyn Amos, graduate student at VT, tested two multi-action insecticides against pyrethroid resistant bed bugs.  Both Tandem and Crossfire, a new product from MGK, performed well against these resistant bugs. 
  • Molly Stedfast reported on mattress encasements for bed bugs.  One of her most important findings was that not all bed bug encasements were bite-proof. After stretching encasement fabric over the mouths of glass jars filled with bed bugs, and applying the fabric-covered mouths to the arms and legs of volunteers, many of the bed bugs were able to successfully feed. But as Stedfast noted, bite resistance is not an issue for box springs.  Nor may it be that critical for bed mattresses either.  Bed bug mouthparts are only about 1 mm long, so once covered with a mattress protector and sheet, the average sleeper should be well protected from any bed bugs trapped in a tight encasement.  Tight zippers and rip resistance are probably more important features when selecting an encasement. 
  • In the category of really-interesting-science-that-may-not-have-an-immediate-application, Dr. Rachel Adams, University of California-Berkeley, talked about the microbial diversity of homes.  The ability of science now to take DNA swabs and identify 40 microbes from one's forehead has rapidly progressed from my college microbiology class where "cutting edge" meant plating out and isolating a few microbe colonies on Petri dishes. This new technology means we can now isolate hundreds or thousands of fungi and bacterial DNA from the average home. The challenge we have today is understanding what these microbes are doing.  Are they reproducing, or just there because they floated in from outdoors?  And what are their human health impacts, if any? We know that microbes can positively or negatively affect our health, allergies and possibly ability to ward off disease.  One example Dr. Adams gave was the so-called 'farm effect', where children who grow up exposed to bacteria associated with cows and manure have asthma rates as much as 4X lower than urban-raised children. Insects may play a role in delivery of some of these microbes, good or bad, into homes.
  • Finally,  Dr. Coby Schal, one of the most interesting and creative urban entomology researchers in the country today, spoke about the gut bacteria in German cockroaches (Blatella germanica to us entomologists!). His research has shown that it may be bacteria that are responsible for much of cockroach aggregation behavior.  Cockroaches with their full gut bacterial complement grew up faster, reproduced faster, found mates faster, and were more efficient foragers compared to cockroaches without their gut microbes.  In addition, cockroaches were more attracted to the poop of other cockroaches with buggy guts, suggesting that these microbes might hold the key to developing a better cockroach attractant for trapping and control purposes. And you might be surprised how much cockroach feces humans are exposed to. A colony of 1,000 German cockroaches (a moderate infestation in some restaurants and apartments) produces an estimated 5 grams of feces per night, or nearly 2 Kg (4 lbs) of feces a year. These same feces contain 7.5 million units of Bla-g antigens, which can cause allergies or asthma in humans in amounts as little as 8 units.
Now you know what urban entomologists talk about when they get together. The subject matter may be boring, humorous or even distasteful to the average person; but be thankful that someone is interested in this stuff.  As for me, I'm glad there's at least one place where everyone knows my name. Cheers!

Saturday, May 7, 2016

Elimination of tree holes for mosquito breeding

Tree holes near ground level are especially
attractive to the Aedes mosquitoes that may
spread Zika virus.
It seems you never know what interesting places and topics pest control will lead you. This week's rabbit trail for me was a discussion on how best to "fill tree holes" that are a common mosquito breeding site.

With the heightened interest in mosquito control and Zika virus this summer, tree holes are a significant problem. When a limb dies back or fails on a tree, the result is often a pocket in the tree that is capable of holding water. It turns out that such water-filled tree holes are perfect breeding sites for some mosquitoes, including Aedes albopictus and Aedes aegypti, the two potential Zika-carrying mosquitoes.

The standard mosquito control recommendation is to fill these holes to prevent their use for breeding. But how do we best eliminate such holes without hurting the tree?  Here are some practical suggestions on filling tree holes gleaned from colleagues and other reputable resources:
  • Filling tree holes with concrete, gravel or sand is a no no. Gravel and sand may help hold water in the tree and promote decay.  Gravel and concrete pose a real safety hazard for arborists or tree owners when the tree eventually has to be cut down--and not good for the chain saws either.  Concrete also adds weight to the tree, and does not flex or bend, causing internal friction and damage to the tree over time.  
  • Drilling drain holes to keep water from accumulating is no longer generally recommended, as it may open the tree up to further damage to health tissue, and infection. 
  • If a tree hole does not hold water it may be providing wildlife benefits, providing a home for birds or squirrels(!).  On the other hand, tree holes may provide a nesting site for roof rats. 
  • Not all tree cavities need to be filled.  However if a tree hole is retaining water or providing a breeding site for unwanted animals, expanding foam may be a good solution. This tool has been largely embraced by the tree care industry because it is lightweight and easy to carry into a tree and is safe for chainsaws.  It also excludes water and will flex and bend with the tree.  Some argue that foam is bad because water often finds it way in anyway and foam retards evaporation, but from a mosquito control perspective the benefits of sealing water-retaining holes probably outweigh the risks.
  • As when using expanding foam indoors in a home, don't overfill a hole. Use a foam with a lower expansion ratio, and inject the foam slowly.  Because foams can be unsightly where they emerge from a cavity, you might want to consider a black tinted foam like Pur-black and/or consider smoothing off excessive foam overflow after drying.
  • If rats or mice are an issue, using screen or or other pest control excluder materials in the filling may prevent their chewing their way back into the tree.
  • It is not necessary to clean out decay from the cavity before filling.  And "tree paint" dressings are no longer recommended by arborists for fresh wounds on a tree.
Thanks to colleagues on the Ornaent Listserve for their interesting and enlightening comments on this question this week.  

BTW, since I've done it here today, referral to a commercial product or website is for informational purposes only and does not imply endorsement by me or by the Texas A&M AgriLife Extension Service.