Ten years of life with the Green Menace

This summer marks an anniversary of sorts.  Shortly after I joined the faculty at Michigan State University in the fall of 1999 MSU Extension began to get reports of dead and declining ash trees in and around Detroit.  Since ash trees had relatively few serious pest issues and none that routinely caused mortality, the mysterious ash decline was attributed to cumulative environmental stresses, ash yellows or various site factors.  In the summer of 2002, however, a little-known exotic beetle from Asia, emerald ash borer (Agrilis planipennis) was identified as the causal organism.  The beetle was so obscure that the first insects collected had to be sent to an entomologist in Eastern Europe for identification.  The summer of 2002 has become a point demarcation for those that work in landscape horticulture or urban forestry in the Midwest and East; now it’s before EAB and after EAB.  Prior to 2002,  EAB was completely unknown in the US, today it has been identified in 15 states and 2 Canadian provinces.

EAB range June 2012

In the intervening 10 years we have learned a lot about the beetle.  In fact, it seems likely that we have learned more about EAB in 10 years than just about any tree pest in history.  I did a quick Google Scholar search and there have been nearly 600 articles published with ‘emerald ash borer’ in the title since 2002. Below are some highlights of what we’ve learned.

In lower Michigan, EAB is able to complete its life cycle in one year.  Adults emerge in early summer, feed on ash tree foliage, mate, and lay eggs on ash tree bark.  When the eggs hatch the larvae burrow into the tree and feed on phloem under the bark leaving extensive galleries.  The larvae eventually pupate and overwinter before emerging as adults the next summer, leaving a characteristic D-shaped exit hole.

EAB life cycle – National Plant Gemplasm System

Host range.  When EAB was first discovered very little was known about the insect, even in its native range in China and Korea.  At the time, information from its native populations suggested that EAB could affect trees outside the genus Fraxinus.  Research in the US, however, has clearly demonstrated that EAB adults can only feed on Fraxinus foliage and EAB larvae can only develop by feeding on ash tree phloem.  So there is little likelihood that EAB will ‘make the jump’ to other tree species outside of Fraxinus.  That’s the good news.  The bad news is that all North American ashes are susceptible to EAB.  There are some differences in relative susceptibility; green ash trees are probably the most susceptible, while blue ash trees will hang in there the longest. Eventually, though, all North America ashes will succumb.

How not to stop an exotic invasion.  While much of what we’ve learned about EAB has been through systematic research, we have also learned by trial and error.  Immediately after EAB’s discovery regulators decided the best approach was try to eradicate the pest.  Historically eradication efforts have not been very successful but decision-makers at the time may have been buoyed by the recent successful eradication of Asian long-horned beetle in the Chicago area.  To make a long story short, EAB eradication failed.  In 2002 the EAB infestation was made up of a core population in and around Detroit and a series of isolated outlier populations.  The eradication strategy was analogous to fighting a forest fire – build a perimeter around the main hot spot and eliminate outlying ‘spot fires’ as soon as they appear.  With EAB the fire fighting analogy broke down for two reasons.  First, it was impossible to contain the main population since the insect was continually carried out of the core area, largely by campers moving firewood (It’s a Michigan thing).  Secondly, fire-fighters can rapidly respond to isolated spot fires because smoke identifies the location almost immediately. With EAB there is typically a 2-3 year lag period once the beetle moves into an area until trees begin to show symptoms.  By that time the population is well established and has likely already spread beyond any potential containment. 

Saving your ash. In 2002 there was no data on effectiveness of insecticides against EAB.  Therefore researchers and extensions specialists, did not provide recommendations for arborists to control it.  Several arborists ignored our advice and treated trees in the core infestation areas in Detroit with insecticides.  In some cases those trees are still alive.  So were the arborists right and were we wrong?  I think both groups did what they had to do.  As scientists and extension specialists we can’t make recommendations in the absence of data.  In many cases the arborists took a ‘sledgehammer’ approach, using multiple products and multiple applications. They saved some trees but they probably used more chemical than they needed to and probably hit some beneficial and other non-target insects along the way.  Today, with the benefit of nearly decade of research, we have effective controls for individual trees, primarily using trunk-injected systemic insecticides.


What’s next.  The range of EAB continues to expand.  While it is possible to protect individual trees, we need to remember those trees will require treatment in perpetuity to survive.   The development of hybrid ashes – similar to what has been done with elms – seems like to most likely scenario that will get ashes back into the landscape.  In the meantime, EAB joins chestnut trees and elms as another reminder of the need to diversify our landscape in order to reduce risks associated with exotic pests.

A Tale of Two Herbicides

I performed a little demonstration the last few weeks which I thought you might be interested in seeing.   So here it is:

I took a little weedy spot of land out in the nursery and divided it into four sections.  Three weeks ago I applied Round-up to one of the sections and vinegar to another.  Then, a few days ago, I applied vinegar (again) to the third section and Round-up (again) to the fourth.  Then yesterday I took pictures of all four sections.  I conducted this little experiment so that I could demonstrate to a group what happens over time after you apply these chemicals.  The results are below.

Above is the Round-up treatment a week or so after application.

And here’s the Round-up after three weeks.

The Vinegar after a few days.

And the vinegar after three weeks.

Vinegar is great for little weeds, but boy oh boy, once they grow up, vinegar just doesn’t do it.

Of Football and Forests

 Howdy all – I’ve been on vacation and then inundated by all that accumulates whilst on said holiday. Here’s a whopper of a belated post. What follows is an account of events you may find interesting (or amusing, or frustrating).

Here’s a portion of a recent press release from the media office at Virginia Tech, regarding our making the "Green Honor Roll."

BLACKSBURG, Va., April 25, 2012 – For the third consecutive year, Virginia Tech ranks among the most environmentally responsible colleges in the United States and Canada, according to the Princeton Review, receiving the highest possible score given by the organization.

The Princeton Review’s Guide to 322 Green Colleges: 2012 Edition, released April 17, profiles institutions of higher education that demonstrate a notable commitment to sustainability in their academic offerings, campus infrastructure, activities, and career preparation. The Princeton Review, in collaboration with the Center for Green Schools at the U.S. Green Building Council, evaluates colleges and universities and assigns a numerical score on a scale of 60 to 99. 

Virginia Tech received a score of 99, earning the distinction as one of 16 colleges to be named to the Princeton Review’s 2012 Green Rating Honor Roll

“Virginia Tech continues to be totally committed to campus sustainability," said Denny Cochrane, Virginia Tech’s sustainability program manager. "Our inclusion on the Green Rating Honor Roll shows how wide spread the commitment is among out students, faculty, staff, alumni, and university leadership."


The story of “Stadium Woods” is interesting and complex.  Virginia Tech Athletics announced the construction of an indoor practice facility for football on part of an 11-acre wooded site, behind Lane Stadium and abutting the current practice field (hence “stadium woods”).  The campus Landscape Architect brought it up at a meeting with the campus Arboretum Committee, who were not thrilled. Virginia Tech has followed a plan of very concentrated/intense land use to keep everything within walking/running distance for the students, and this was one of the few wooded areas left.

The committee proposed an alternative site a few hundred yards away, with the new facility replacing some tennis courts and a roller-hockey rink. 

This suggestion was not met with great enthusiasm by the Athletics department.

Two possible sites for indoor practice facility, adjacent to practice field where 200-300 year old trees are, or along Washington Street on top of some tennis courts (also possibly 200 years old).

At that point, an immense hoo-ha began that would stretch over a year.  I’m going to leave out the ensuing committee/administrator/athletics blow-by-blow, but in a nutshell, some of the Forestry faculty determined this was not just “woods” but a rare stand of old-growth forest, and the Athletics folks were insistent “this is absolutely the best place for the facility!”   Football is huge at Virginia Tech, thus anything described as giving an edge in recruiting gets maximum priority.  In the event of a thunderstorm, having the student-athletes run an additional 150 yards from the practice field to the alternative indoor facility location was just not acceptable. Other issues included digging up a ton of infrastructure (steam lines, electric, etc.) that runs along the road, plus the height of the proposed building does not conform to the campus Master Plan (since it’s for football, it has to be be tall enough to kick a field goal in. We really do need a lot of practice at that.) Guesstimates are around $1million increase to account for the infrastructure issue (added to the $15 million estimate for construction).

A community group “Save Stadium Woods” was formed, complete with a (very nice) website and a letter-writing campaign to the local newspaper. There were petitions, resolutions from everybody and their mother, and more.  The local coverage was intense plus there was a letter to the editor in nearly every newspaper issue for the past three months. CNN even covered the story, which was great, as no campus shootings were involved for the first time in a
while.  One of the 300+ year old white oaks was named “Stephen Colbert” in an effort to raise awareness (?!?).  

An ad-hoc committee of university administrators, both Athletics and non-, plus interested parties from both the faculty and the community was charged by the President to come up with a solution. 

And of course, a third-party consultant was brought in, because we apparently don’t have enough smart people here on campus.

Yes, quite the head-scratcher… place the building and site footprint on top of 3 acres of steeply-sloped, old-growth forest? Or remove some aging and underused tennis courts, which could be relocated to the intramural athletics area on the fringe of campus. Yet Athletics continued to argue, and University administration was silent.

The committee weighed in a week ago, coming to the logical conclusion of protecting the woods and utilizing the tennis court site.  I guess the weirdest part of this is that something so no-brainer-ish was allowed to drag on and on, giving our beloved Virginia Tech and so-called “Green University” (complete with TreeCampus USA designation) a black eye. 

Groundcovers for gaps

I promised on last week’s post that I’d mention some other low-input methods of keeping weeds out of the gaps between paving stones.  Here are a few photos of my own yard, where we’ve been installing flagstone pathways and terraces.  (Money-saving hint: check out craigslist and/or freecycle for free pavers and other types of stone.  We got all of ours free – just had to pick them up.)

We bought flats of groundcovers, such as woolly thyme, Irish moss, and blue star creeper.  In sunny areas, these plants thrive and spread quickly. But in shadier, moister areas they haven’t done so well.  Instead, we’ve allowed nature to fill the gaps for us.  Naturally occurring mosses, ferns, and other small plants keep out annoying weeds yet are small and attractive in their own right.

You can jumpstart the process by making a moss “milkshake” to spread between pavers.  There are recipes on the web, so I won’t bother repeating them here.  I prefer to let nature take its course (or maybe I’m just lazy).

Hot new method of weed control?

There’s a new report out from University of Copenhagen on killing weeds between paving stones. What they recommend is burning or steaming the weeds lightly and repeatedly. Boiling water, steam, even flamers can be used to wilt the leaves over the course of several treatments (six was recommended). This process damages the leaves beyond repair, slowly starving the roots to death.

I’m not sure exactly how I feel about this study (which is getting a lot of attention on the internet). On one hand, it is a chemical-free way to kill weeds…but on the other hand, it’s pretty labor intensive and requires energy inputs for generating heat. Moreover, what does one do once those weeds are gone? Those bare patches of sterilized soil are just going to be recolonized by new weeds.

Several years ago I had a Master’s student look at different methods of killing English ivy. She also tried the steam treatment.  Ivy laughs at steam. Aggressive perennial weeds like English ivy or blackberry or Japanese knotweed are unlikely to be much affected by blanching, and certainly not by half a dozen treatments.

But most of us probably don’t have big, woody-rooted weeds amongst our paving stones.  In my own garden, it’s a mixture of species that fill these gaps and some of them – like mosses and some smaller ferns – I actually enjoy.  So I pull out the things I don’t like, leaving the desirable species to fill in the gaps.  It’s simple and requires no special equipment.

Am I missing something here, or is this really much ado about nothing?

How open-minded are you? No, really.

Admitting you’re wrong is difficult.   For exhibit A see the recent discussion between me and Jeff over alternative nursery containers.  We all like to think we’re open-minded but  when push comes to shove we all end up like the Fonz on Happy Days when it comes time to say ‘I was wrrrrr… I was wrrrr….  I was not exactly right.”  http://www.youtube.com/watch?v=uwkU8-d1gIk   As scientists we’re supposed to be objective and base our judgments on verifiable data and careful and repeatable observations.  But, as humans, we all have biases and preconceived notions that are hard to get around.

So here’s a challenge for our Garden Professors readers (and my fellow  GP’s too).  Give an example of a case where you’ve changed your mind about a landscape or gardening practice or product.  And what did it take to change your way of thinking and make you say, “Ya know, maybe I was not exactly right.”

I’ll start.  I have long been dubious about is the use of plant growth retardants (PGR’s) on landscape plants.  PGR’s are chemicals that reduce plant growth, usually by inhibiting shoot elongation.  There are a variety of PGR’s on the market but most work by inhibiting plant growth hormones such as gibberilin or auxins.  PGR’s have long been used by bedding plant producers to make plants more compact and easier to handle and ship.  One PGR, paclobutrazol, has been heavily marketed in recent years to control growth in landscape trees and shrubs.  The effectiveness of paclobutrazol at controlling plant growth has been well established in the literature, though there are some exceptions.  My long-held skepticism toward the landscape application of PGR’s stems from a couple factors.  First, the marketing claims are pretty fantastic: Not only does it control growth but it improves drought tolerance, heat tolerance, insect resistance, and disease resistance (no word on how it does on getting spots out of rugs).  Second, just because something works on containers of annuals in a greenhouse doesn’t mean it will work on trees and shrubs in the field with variable soils, weather, etc.  Third, why bother?  If something is growing too fast; back off the fertilizer, head it back with the Felco’s, or take it out and put something more appropriate there.

What changed my mind.  I’ve seen a couple of effective applications of PGR’s on trees and shrubs that have made me re-evaluate my opinion.  One was at a program at the Indiana Arborists Association a couple years ago.  The study tracked pruning cycles following utility line clearance pruning.  They found that treating trees with paclobutrazol following pruning reduced re-sprout growth and extended the cycle time between pruning by 2 to 3 years – which is a big deal to utility arborists.  More recently, I’ve been observing shrubs here on campus that our landscape service group has been treating with paclobutrazol after pruning.  Typically many shrubs are rejuvenated after pruning and put on a big flush of growth.  The PGR application was effective in keeping this in check.  (Some examples with burning bush appear below). Even to my highly skeptical eye, the treated plants just looked a heck of lot better than the untreated.

Do I believe all the marketing claims made about PGR’s for landscape plants?  No. But for extending pruning cycles and keeping plants in check, I have to admit I was not exactly right. 

Burning bush with PGR app.

Burning bush without PGR app. (Note treated and untreated were growing in same bed)

By controlling growth after pruning PGR application can help keep these shrubs in line and lengthen the time between pruning cycles.

Are Goodies Bad?

I can’t decide if I like the fact that various companies read what I write or not. On the one hand, it’s kind of nice to know they care, but on the other, I kind of like to think that I can talk to people without them hanging over my shoulder.

How do I know they’re there over my shoulder?

They send me stuff.  Sometimes it’s a nasty or "educational" e-mail after I’ve published something about their product that they don’t like, and sometimes it’s a gift bag (or an offer of a gift bag) if I mention that I like something.

I never respond, with one notable exception.  Once I wrote a little something on bees for a newspaper and a small honey operation went out of their way to drop off some honey for me at the front desk.  I thought that was really nice so I wrote them a quick thank-you. 

I wrote something nice about Milorganite recently and they sent me a ballcap, some pens, and samples — along with some literature.  That was nice, but I feel like it wouldn’t be appropriate for me to write back.  I do like Milorganite, but if I start to think of them as my "friends" I don’t know how impartial I’ll be able to be if I find something out that changes my opinion.  I will use the free sample though.

On the boo-hiss side I had the lawyer from company in town call a newspaper where I published a story recently to tell them I got my facts wrong and that they needed to publish a retraction.  The company was wrong though — so no retraction was published, but it was still odd to have a lawyer get involved like that.  Will I think twice about talking about that company’s product in the future?  Not consciously.  But subconsciously?  Who knows (shoot — subconsciously it might make me talk about them more — I don’t know).