The ins and outs of trunk injection

I am serving on a Ph.D. committee for a student working in Entomology and Plant Pathology who is defending his dissertation tomorrow morning. I’m taking a break from trying to plow through the longest dissertation in history: A 465 page tome on the use of trunk injection in tree fruit crops. A lot to wade through but a fascinating topic. Trunk injection, of course, is not a new topic. Some of the earliest references to injecting compounds into trees date back to Leonardo daVinci, who also suggested the ‘pipe model’ theory of tree architecture; the notion that total cross-sectional area of a tree is constant as you move up to higher and higher levels of branching.

daVinci's notes on branch architecture
daVinci’s notes on branch architecture

Trunk injection can be useful in lots of applications. We have done some research in my lab on the use of trunk-injected imidacloprid for treating ash trees for emerald ash borer. The compound is highly effective against the beetle but using C-14 radio-labeled imidacloprid we were able to demonstrate the flow up the trunk of ash trees can be ‘sectored’, potentially resulting in ‘hot’ and ‘cold’ spots in the crown where the adult beetles feed on leaves.

Injecting 14C-labeled imidacloprid into ash trees.
Injecting 14C-labeled imidacloprid into ash trees.

On the MSU campus our arborists have been successfully using trunk-injected fungicide applications to protect our remaining elm trees from Dutch elm disease (DED). Prior to the arrival of DED the MSU campus had about 3,000 elm trees; today we have less than 300. Under the current program the trees are treated with propiconazole in a three-year rotation; 100 trees each year. We still lose a tree or two each year but the program is largely effective.

Elm trees used to be a dominant feature of the MSU campus, now they are specimens.
Elm trees used to be a dominant feature of the MSU campus, now they are specimens.

One application of trunk injection of which I am dubious is for treatment of nutrient deficiencies. It’s not that trunk injection is not effective for this purpose; in fact, it is often highly effective. The problem is treating nutrient deficiencies with trunk injection just treats the symptom rather than the underlying cause. Here in the Midwest a common scenario is iron chlorosis in pin oaks. The fundamental problem is that alkaline soil conditions limit iron uptake. The solution? First, right tree – right place. Don’t plant pin oak if you have alkaline soils. Second, if it’s an existing tree, work on lowering the pH with sulfur or ammonium sulfate. Remember, trees have evolved or God designed them – take your pick – to take up nutrients through their roots. Dealing with that end of the equation is the best solution in the long run.

Trunk injection can be used to treat iron chorosis but can sometimes cause more problems.  Injection of ferric ammonium sulfate burned leaves on this tree.
Trunk injection can be used to treat iron chorosis but can sometimes cause more problems. Injection of ferric ammonium sulfate burned leaves on this tree.

Brace yourself

The photo below (graciously sent to me by former MSU Extension Educator Jennie Stanger) graphically illustrates the importance of removing ALL staking and supporting materials from trees once they are established.



Just a matter of time (Photo: Jennie Stanger)

In this case the stakes were removed but the strapping material was left around the tree.  Since this is a spruce, Jennie supposes no one wanted the prickly job of wading into the center of the tree to take off the strap.  Eventually the trunk was girdled and when the area recently experienced some heavy thunderstorms, the weak spot on the tree was exposed.



Stately evergreen to mangled mess (Photo Jennie Stanger)

As a general rule we recommend that all staking and support materials are removed within two years, preferably one year.  This type of damage is one of the prime reasons: after two years who is likely to remember that there is still strapping left on the tree?

The heartbreak of ‘Carrot-top’ syndrome

The perk of participating in a blog is you get a platform to vent on your pet peeves.  Recently I’ve seen several classic examples of ‘Carrot-top’ syndrome.  No, I’m not talking about the red-headed comic; though he tends to annoy me too.

Annoying Carrot-top #1.

The ‘Carrot-top’ I’m referring to occurs when white pine trees are sheared as Christmas trees but then planted as landscape trees.  The typical result is that the side and lower branches remain suppressed while the terminals go crazy.  I’m not sure why syndrome occurs in white pines and not other trees; it may be related to vigor of white pines and how hard the growers have to shear them to keep them in shape.


Annoying Carrot-top #2.

I love my friends in the nursery and Christmas tree industries and they work hard to grow quality trees, but this is one practice I’d like to see end.  And, to be fair, they are giving customers what they want.  If we set up a survey at a garden center and placed  a 7’ sheared white pine next to a 7’ white pine that had been minimally pruned, 19 out of 20 people would take the tree that had been sheared to look like a Christmas tree.  However, this is truly a case where less is more.

Going off half-cocked

The good news about being a landscape extension specialist is you get to comment on a variety of landscape tree problems.  The bad news?  You get to comment on a variety of landscape tree problems.  In an average week I probably get 10-15 tree-related calls or e-mails from homeowners, landscapers, growers, extension educators, lawyers, newspapers, and on and on.  Sometimes the problem is routine and obvious like tar spot on maples; “I have these spots that look like tar on my maple leaves…”  Sometimes the problem looks routine and turns into something else entirely different like the Imprelis herbicide debacle.  With the number if problems I respond to, invariable I sometimes end up shooting from the hip – and miss the mark.

Red maple with sparse canopy (right foreground).  Maple in left-center of picture across the road was planted at the same time.

A few weeks back I noticed some red maples on campus that were struggling as they were starting to leaf out.  There were planted about three years ago following a road-widening project.  They are located on a tough site between a parking lot and a busy 4-lane road.  My immediate diagnosis was they were weakened due to the aftereffects of last year’s sever heat and drought.  I even included a photo of them in an article I did for our on-line extension news.  Then this morning I happened to talk to a friend from our campus landscape services.  “Boy, those maples sure took a beating from the drought last year”, I volunteered.  My Landscape services friend replied, “Well, that and we hit them with Shortstop last year…” Uh oh, now the conversation was going in a different direction.  Shortstop is a plant growth retardant, the active ingredient is paclobutrazol, which inhibits GA synthesis in plants and is being widely used by arborists to reduce the need for tree pruning.  In this case it worked a little too well and the trees ended up being stunted.

Leaves of paclobutrazol-treat maple (left); untreated leaves on right.

In my defense, I was partly right.  Under normal weather patterns paclobutrazol applied at the labeled rates (as was done here) would have reduced shoot growth and leaf growth but clearly the drought exaggerated the effect.  So, another lesson learned (actually re-learned) never assume anything about trees until you talk to the people who actually take care of them.

You don’t have to be crazy to work here, but it helps

Recently I spent a week in Oregon working on a Christmas tree genetics project along with my colleagues Chal Landgren( Oregon State University), Gary Chastagner ( Washington State University), and John Frampton (North Carolina State University).  The objective of the project is to identify superior seed sources of Turkish fir and Trojan fir for use as Christmas trees around the United States.   We refer to the project as the Cooperative Fir Genetic Evaluation or CoFirGE – remember, the most critical step in any experiment is coming up with a catchy acronym.    CoFirGE began with a trip by my colleagues to Turkey where they collected seed from 100 fir trees across a range of sites in Turkey

Turkish fir growing in western Oregon

Why are we interested in these species? Both Turkish and Trojan fir are closely related Nordmann fir, which is widely used as a Christmas tree in Europe.  These species make wonderful Christmas trees due to their symmetry and needle color.  In addition they may be resistant to diseases, particularly Phytophthora root rot, that plague Christmas tree growers from Washington State to North Carolina.

So, what was going on in Oregon?  After the seed were collected in Turkey they were sent to Kintigh’s nursery near Eugene, Oregon, where the seed were sown to produce seedling plugs.  The next step of the project will be to send the seedlings out to cooperators in five locations (Pacific Northwest, Michigan, North Carolina, Pennsylvania, and Connecticut).  This is tree improvement on a grand scale.  In each region there will be two test plantings and each planting will include 30 reps of 100 seed sources or 3,000 trees.  Multiplied by 5 regions and 2 plantations that’s 30,000 trees total that we will collect data on for the next 8-9 years.

30,000 seedlings ready to be sorted and shipped

Each seedling is individually labeled with a bar code for identification

Sorting into to boxes to send to cooperators around the country

But step one is getting the seedlings from the nursery to the out-planting sites.  That means lots of tagging, sorting, and bagging.  With help from technicians and students from WSU, OSU and NCSU and staff from Kintigh’s we were able to get all the seedlings sorted and bagged by mid-day on Thursday and start them on their journey to their new homes.  Next  step: Planting…

What’s a view without trees?

A while back I wrote about a Seattle-area neighbor dispute over a tree partially blocking their view.  Sadly, the tree lost out in this case, which was decided a few weeks ago.

Now a second tree vs. view dispute was reported this week.  You’ll have to read the story to see how many things are inaccurate/indefensible/infuriating about the “trimming” of this 90 foot western red cedar (a native species).  My personal favorite: “the tree violated neighborhood bylaws ensuring no house’s view would be blocked.”

I wonder how they got the tree to agree to the bylaws in the first place?

A western red cedar (Thuja plicata), maybe 60 feet tall.  People in my neighborhood like their big trees.

Selection and Protection: Preventing the heartbreak of splayage

We’ve had considerable discussion over on the FaceBook site concerning snow damage to columnar arborvitae.  This is a common phenomenon resulting in a condition Holly has dubbed ‘splayage’.


The question, of course, is what to do about it?  My standard response to addressing most problems related to winter injury is there are two options: selection and protection.


Selection means putting the right plant in the right place.  For columnar arbs this means not planting them in areas prone to wet heavy snow.   Here in mid-Michigan we get a wet snow about once every other year.  Last winter we had a 10” of snow in Nov. 30 that resulted in a lot of tree breakage, including arbs.  The problem is the branch structure of columnar cultivars such as ‘Holmstrup’ or ‘DeGroots spire’ cannot bear up to the snow weight.  Remember these are cultivars that were specifically selected for their upright branch habit, this is not the natural branch pattern of the species (Thuju occidentalis or Thuja plicta depending on the cultivar).  There are, however, some narrow trees that are adapted to sloughing off heavy snow.  For example, most forms of Alaska false cypress (Cupressus nootkatensis) will do well under heavy snow loads.  Also, weeping white spruce (Picea gluaca ‘Pendula’) is a good narrow conifer for snowy locations.


Alaska falsecypress (right) is adapted to heavy snow. Notice how snow hangs on other conifers on the left.

But what do you do if you already have a row of columnar arbs and you live in an area prone to heavy snow? Protecting trees from bending over by tying up the upper 1/3 is often the only reliable option.  Note that the all ties or wrap need to be removed in the spring.  Yes, it’s a lot of work.  Makes the ‘right tree right place’ thing sound better.  Note that you only need to provide enough support to keep the branches together, you don’t need to wrap the entire tree like a mummy.


I want my mummy…  Does this work?  Probably.  Question is do you want to look at it all winter?

What about repairing damage after trees have splayed?  Some arborists I’ve talked to about this problem have had success tying up tops after the fact provided the trees are tied before any new growth occurs and the branches are bent, not broken.  It is important to remember that this  is similar to situation with standing and  guying up trees after a windthrow event.  Yes, you can stand the tree back up but how are you going to stop it from happening again?  In the case of splayage, you’re into a cycle of tying or wrapping every year.

Happy New Year

As trite as it sounds, I try to slow down and enjoy the simple things around the holidays.  We are starting to get some more seasonal weather, which means cold temperatures and occasional snow flurries.  Once we get our first real snow cover I pull out my birdfeeder from beneath the shop-bench in the garage, fill it up and set it in a beech tree outside our kitchen window.  No one in our family is a birder but it’s interesting to see how nearly everyone takes time to linger over their morning coffee or tea to watch the steady parade of chickadees, nuthatches, cardinals, and jays at the feeder.   The feeder itself has some sentimental meaning as well. I bought it at an auction for the Arboriculture Society of Michigan meeting several years ago and it was handmade by Dan Kurkowski, longtime city forester for Detroit.  Dan was a tireless tree advocate for the Motor city who passed away, much too young, six years ago but I always remember his passion for people and trees.  And every time I set out the feeder he built I remember how he closed every e-mail with the line for the Lorax, “I speak for the trees for they have no tongues.”

I hope everyone enjoys a quiet and restful end of their holiday season.

What would YOU do?

Once in a while we end up flicking around the dial on Friday evenings and land on a show called “What would you do?”  It’s a hidden camera-type set up where viewers get to see the reaction of everyday folks faced with awkward or contentious situations like an overbearing customer berating a waitress over a minor mistake in their bill.  The scenarios are played out by actors but the people responding are not.  Personally I find the premise of the show slightly annoying because it smacks of entrapment but it seems to lure in the rest of my family.

Today we’ll do our own version of “What would you do?”  In this case, however, the situation is real.  Here’s the deal.  Michigan State University has begun work to complete the Facility for Rare Isotope Beams or FRIB across the street from the Horticulture building.  This $615 million dollar project will enable physicists to study rare nucleotides, the kind of elements that only exist for fractions of seconds.  It’s definitely big science stuff and can lead to all kinds of exciting discoveries.  In looking at some of the plans for the FRIB, however, some of my colleagues discovered that the FRIB completion will require removal of several large mature oak trees that close to 100 years old.  The initial effort to save the oaks focused on re-locating the portion of the FRIB that conflicted: No dice.  The next option was to move the oaks.   Due to various factors, only one tree, a bur oak about 3 feet in diameter, can be moved.  The price tag: approx. $150,000.  The move date is currently set for Dec. 10.  Now another option has surfaced: remove the mature oak and use the $150k to plant new trees around campus.  Our landscape services typically plants 2” caliper shade trees and 6’-7’ conifers so we’re probably talking 400-500 trees.  I am part of a group that will try to hash things out on Wednesday.

So, what would YOU do?  Save one large mature tree or plant 400+ new?

Here’s a look at the oaks through the years…

Today. Oaks trees are located in median in center of the image.

1980 during construction of the Wharton Center for Performing Arts



Finding agreeable things not sought for

As a graduate student at the University of Georgia many years ago I took a course in research methods.  One of the discussions that stuck in my mind all these years centered on the word ‘Serendipity’.  The classic definition of the word is “the faculty or phenomenon of finding valuable or agreeable things not sought for.”  As scientists we rely heavily on the scientific method as a systematic method of inquiry to make new discoveries.  But we also need to need to keep our eyes and minds open to serendipitous discoveries along the way as well.  

So what got me thinking about serendipity?  A few weeks back I visited a Christmas tree grower in northern Michigan with Jill O’Donnell our state-wide Christmas tree educator.  The grower called us in because he had some questions about some unusual trees in one of his Fraser fir plantations.  And, not only were the trees unusual, they were gorgeous.  The only question was; what were they?  The plantation originated from seed the grower had collected himself from some older Fraser fir trees he kept as a seed orchard.  He sent the seed to a large forest nursery in the Northwest, which grew the seedlings and sent them back to him.  The grower wondered if seed of another species could have been introduced in the process.  Possible, I told him, but not very likely.  Nurseries that are serious about contract growing are meticulous in keeping seed lots separate – few things are worse in that business than sending the wrong seedlings.  Plus, I’ve worked with many species of fir and this was one I didn’t recognize. The trees had many characteristics of Fraser fir but also had attributes of concolor fir; long bluish needles and a slight hint of citrus scent when the needles were crushed.  Many fir species can hybridize and all I could think was these trees had to be hybrids.  “Are there any mature concolor firs near the seed orchard?” I asked.  The grower brightened, “Actually there’s a group of older concolors about a half mile up the hill from the Fraser fir orchard.”  We jumped in his pick-up and visited the concolor firs.  Many of the trees had cone stalks indicating they were reproductively mature and could produce pollen.  Conifer pollen can travel for miles so it’s reasonable to expect that some of the concolor pollen could reach the Fraser firs, which were downhill and downwind based on the prevailing winds in the area.

Excellent tree form of the mysterious hybrids

So what’s next? There are several reasons to follow up on this serendipitous discovery and try to make some additional crosses.  First, as evidenced by the photos, the trees look fantastic.  Second, Fraser fir and concolor fir are each great trees but they also have some liabilities.  A downside of concolor is that they break bud early and often suffer late frost damage – Fraser’s break bud late.  Fraser fir need acidic, well drained soils – concolor fir can grower on a broader range of sites. It’s possible that the hybrids will have intermediate characteristics that would make them ‘the best of both worlds’. 

Foliage close up

The only thing left is to decide what to call the hybrids.  Nurseries like to combine common names. So, Craser fir?  Froncolor?