Imprelis damage to landscape conifers

Herbicide issues seem to be dominating my life these days. Over the past several weeks reports have surfaced around the Midwest of landscape conifers – primarily spruces and pines – that have developed rapid and severe die-back. While there are a host of insect pests and pathogens that can cause die-back in conifers, the recent cases are noteworthy in the speed with which trees expressed symptoms.


Photos: Andy and Carol Duvall

In many cases that have been reported the common thread appears to be the use of Imprelis, a turf herbicide developed and marketed by Dupont.  Imprelis (active ingredient: aminocyclopyrachlor) is a synthetic auxin designed to control broadleaved weeds in turf.  Ostensibly, one of the advantages of Imprelis is that has root activity in addition to foliar activity.  It appears, however, that it may have too much root activity and the internet is abuzz with photos and posts of Imprelis-damaged conifers.


So what’s going on?  Well there are lots of blurbs coming out and lots of things being reported second and third-hand.  I suspect a few things we ‘know’ about Imprelis right now will turn out not to be the case in a few months.  Dupont has tried to shift blame to the applicators, suggesting that their rates may have been off, they applied when there was potential for drift, or that the material was mixed with other herbicides.


Given that reports of damage showing similar symptoms have come from Kansas, Iowa, Indiana, Michigan, and Ohio it seems unlikely that everyone is mis-applying the product.  I suspect one of a couple things may be going on.  Dupont may have underestimated the lateral extent of tree roots, especially for conifers that often have shallow, extensive root systems.  It’s also possible that Norway spruce and white pine are more sensitive to this product than whatever Dupont tested it on.


In the meantime stay tuned.  In case people haven’t figured it out for themselves, Dupont now recommends that applicators not use Imprelis near spruces or pines (see letter linked above). Landscapers or lawn service operators that have applied Imprelis should keep in touch with their state Department of Agriculture and their professional turf and landscape association.  Might be good to fasten your seatbelts, this could be a bumpy ride…

Warning: This blog may be hazardous to your health

Following up on Jeff’s post last week regarding blue spruce.  Jeff noted, and several posters agreed, that even though blue spruce will eventually have a host of pest problems, for the first 10 years or so it’s a darn good looking landscape conifer.  Jeff went on to draw the analogy that choosing a blue spruce is like choosing sexy sports car or gas guzzler over a boring, high MPG sedan.  To a certain extent the libertarian in me agrees.  If I want to plant a blue spruce in my Michigan backyard or buy a Nissan Titan to commute back and forth to work , by Gawd, that’s nobody’s business but my own.  Of course the difference in these situations is that I have EPA reporting to tell me the Titan only gets 12 MPG in the city; for the spruce, people like Jeff, me, and our highly intelligent readers know what we’re getting into from experience and training.  But what about the public at large?  Maybe what we need are government warning labels for plants.  We have them for cigarettes: “Warning: Smoking Causes Lung Cancer, Heart Disease, Emphysema, And May Complicate Pregnancy”, though the European warning, “Smoking kills” is more direct and to the point.  We also have warnings for side effects of prescription medications; “may cause nausea, vomiting, headache, hearing loss, oily discharge, an erection lasing four hours, and thoughts of suicide”.  Think I’ll take my chances with the disease, thank you.  


So what kind of labels do plants need?


Blue spruce:  Warning this plant will look great in your yard for 10 years and then fall apart when it becomes a magnet for gall adelgid and loses half its limbs to cyctospora.


Eastern white pine:   Caution: This little guy looks like a cute little Christmas right now but in 10 years it can devour your house.


Silver maple:  Warning:  Don’t blame us when this tree comes crashing though your house during windstorm.


Sweetgum:  Caution: Be sure to retain a good attorney for when your neighbors start tripping over gumballs on the sidewalk.


That’s a start. What plants do you think need warning labels?

Porsche 911 or Toyota Camry

Earlier today I was in a meeting with some other professionals from across Minnesota (and a few from Wisconsin and other areas) to discuss the disease problems of conifers.  Our discussion quickly became focused on the use, and overuse, of Colorado blue spruce, a tree that just doesn’t do well in Minnesota — Or Michigan from what Bert has written!  Everyone in the meeting was yammering on about how we need to educate nurseries and consumers about how terrible the Colorado blue spruce is in our environment — you’re lucky if you can get 10-15 years out of the thing before it succumbs to one disease or another.  But, though academics, arborists, and most tree care professionals (including nurserymen) talk about how lousy this tree is, customers want Colorado blue — and if a nursery doesn’t sell it, well then that nursery has lost some business.

I support the idea of warning people away from Colorado blue.  Still, during our meeting I couldn’t help but have this thought running through my mind:

Colorado blue spruce is a unique and beautiful tree — it is bluish in color, tends to have a good form, and is a relatively fast grower (until it succumbs to whatever disease it dies from!).  There are certainly other trees that are also beautiful — but there is no denying that Colorado blue has a distinctive look.  If I were walking through a nursery this would be the tree that I’d want.  If a nursery person told me that the tree was going to have a short life — 10 – 15 years of looking good — I just might be OK with that because there just aren’t that many trees which look as attractive as a Blue spruce in a nursery.  Sure, I could have something that would look OK for 30 years, but, if I’m like most Americans, I won’t even be in the house that I’m living in now in 10 years, never mind 30.

To draw an analogy, You know that a Porsche 911 isn’t the best car to buy — it is a gas guzzler (for it’s size) — it doesn’t have much luggage space (or room for passengers), and it’s less reliable than your typical compact car.  A Toyota Camry is better in all of the areas that I just mentioned.  Still, if I were looking for a car and if they were the same price I have to admit that the Porsche would be too cool to pass up.

Landscape conifers: The Good, the Bad, and the Underused

This week is our annual Great Lakes Trade Expo, the main trade show and education venue for Michigan nursery and landscape industry. One of my talks was for the Arboriculture track on landscapes conifers. The theme this year was “The Good, the Bad, and the Underused.” Hey, you try giving a dozen talks a year for 10 years and see if you can come up with an original title!


The selections were based the following, admittedly subjective, criteria.

The Good:  These are the all-around good guys.  Conifers that are well-adapted, good growers with good form and few pest problems.

The Bad:  The problem children of the conifer world.  Pest magnets, spoiled prima donnas, or incessantly overused.

The Underused:  Trees that have the virtues of ‘The Good’ but that tend not to attract attention.


Here are three of my selections for each of the categories.  I’m interested in nominees from other sections of the country and the world.


The Good:

Eastern white pine Pinus strobus This one flirts with the overused designation but I’ll give it a nod since it’s the state tree of Michigan and figured prominently in the state’s history when Michigan was the lumbering capital of the US in the late 19th century.  A fast growing tree that improves with age.


Eastern hemlock Tsuga canadensis   The answer to the age-old question, ‘What conifer to you recommend for shade?’  A little finicky on site, prefers moist but well-drained – who doesn’t.  But a great elegant looking tree.  The main down side is the specter of hemlock wooly adelgid looming to our south.


Alaska false cypress Chamaecyparis nootkatensis (Xanthocyparis nootkatensis).  Lot of confusion over the nomenclature but no question this is a great landscape tree.  Graceful, weeping habit; good growth rate; and few pests in this area (knock on wood).


The Bad.

Scots pine Pinus sylvestris  Is there a pest that doesn’t affect this tree?  Our Forest Entomologist, Dr. McCullough, had a grad student count up all the pests that affect Scots pine and they lost count after 30.  Borers, tip moths, needlecasts… the hits keep coming.  The problems are exacerbated around here because of abandoned Christmas tree plantations that serve as insect breeding grounds and fungal infection courts.


Austrian pine Pinus nigra  Austrian pine is a frustrating tree.   In some respects it is the perfect conifer for our region. A great looking tree with dark green needles.   Good growth rate, cold hardy, drought hardy, tolerates road salt.  Everything you could want in a tree and then some.  Then the trees get about 15 years old and the wheels fall off.  Diplodia tip blight, dothistoma needle blight…  Austrian pine is the ugly duckling in reverse; looks great when young and then, blechh…


Colorado blue spruce  Picea pungens  The tree everyone loves to hate, yet we keep planting it.  I suppose it’s the allure of the blue that people can’t resist.  It’s like that bad boyfriend; you know he’ll do you wrong but…  He’ll lure you in with those baby blues then start hanging out with those low-life Cooley adelgids, then hook up with rhizosphaera needlecast.  And by the time the cytospora cankers start hanging out you know this relationship is going nowhere.


The underused

Swiss stone pine Pinus cembra  Renowned conifer aficionado ‘Chub’ Harper used to remark, “I never met a cembra I didn’t like.”  Cembras are great trees, good growers with consistently good form.  Underused but worth looking for.


Korean fir Abies koreana  I wrote about Korean when in discussion alternative Christmas trees but it also makes a good landscape tree.  In our area we can expect about 1’ of height growth per year.   Symmetrical form; short needles with silvery undersides, and conspicuous cones.  Lot to like about Korean fir.


Dawn redwood Metasequoia glyptostaboides  A fast-growing deciduous conifer with wonderful pyramidal form.  Dawn redwood is also an interesting botanical story.  Only known to science from fossil records, an isolated population was discovered in China in the 1940’s.  Seed were imported into the U.S. and the tree has been found to be broadly adapted.

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What fir?

OK, it’s the middle of December so I get to indulge my passion for Christmas trees.  One of the most interesting projects I’ve gotten to work on during my time at Michigan State is a study to look at alternative species of firs (Abies spp) for Christmas trees and well as for landscape conifers.  Firs are fascinating trees that are distributed throughout temperate regions of the northern hemisphere.  There are about 50 species, many of which are important for timber, landscaping or Christmas trees.


For those of you that put off your Christmas tree shopping until the end (or want to start thinking about next year’s tree) here are three trees to keep an eye out for.


Korean fir Abies koreana We have several growers in Michigan that are now growing Korean fir.  It has relatively short needles that have a bottle-brush arrangement on the stem.  The color is often described as dark green, but I’d say the needles tend more to a true green or Kelly green with a silvery underside.


Concolor fir also makes a great landscape conifer

Conolor fir Abies concolor  I grew up in the Northwest so I always knew this tree as white fir until I moved to the Midwest.  In any case, it’s a great tree.  Long, soft-blue needles.  Depending on the seed source they can be as blue as a blue spruce.  The main draw-back here in Michigan is that concolor tend to break bud early, which makes them susceptible to frost damage in the spring.  Their citrus-like scent is hard to beat.


Danish growers compete for the best Nordmann fir in the “Fight for the Golden star” at their annual tree fair.

Nordmann fir  Abies nordmanniana  Denmark is the leading producer of Christmas trees in Europe and Nordmann fir is their principle species.  The Danes like Nordmann because of its deep, dark green color and natural form and symmetry.  Europeans don’t like their Christmas trees sheared so they rely heavily on genetics and selection to find trees that naturally have good form. We’re starting to see more Nordmann in the US, both here in the Midwest and in the Northwest.  Growers complain that the trees are slow-growing to start but I think some US consumers are looking for a more open, natural-looking tree and Nordmann can fill this niche.

A lawn alternative we can support: Conifers!

As many of the blog readers are aware, I do a lot of writing about conifers.  In the process I mingle with members of the American Conifer Society or ‘ACS’ for short -although some wag has suggested that ACS actually stands for Addicted Conifer Syndrome, such is the devotion of these enthusiasts for their beloved conifers.  A couple weekends ago I was privileged to attend the first ever ACS ‘Illinois Conifer Rendezvous’ hosted by Rich and Susan Eyre, owners of Foxwillow Pines nursery in Woodstock, IL.  Rich and Susan are a wonderful, enthusiastic couple and conifer addicts of the first degree.  Their nursery boasts one of the largest assemblages of rare and unusual conifers anywhere in the country.  The program for the ‘Conifer rendezvous’ included speakers and tour of the nursery.  The highlight for me, however, was the tour of a couple of local homes featuring outstanding conifer gardens; including the home of Rich’s 92-year-old mother Margaret Eyre.  Margaret is an incredibly energetic woman with a passion for hostas and philanthropy (see the Heifer International link on the Foxwillow Pine website  Margaret decided years ago to dispose of her lawnmower – no small feat since her house sits among homes with vast expanses of lawn typical of the sprawling suburbia that radiates from Chicago.  What to do without a lawnmower? Plant plastic turf?  Margaret had other another idea…

Margaret Eyre’s conifer haven sits like an oasis in the Chicagoland suburban sprawl

I didn’t get an exact count, but I’d estimate Margaret has about 80 to 100 specimens tucked away on a standard-sized city lot.  Most are dwarf or unusual conifers, though several are full sized trees.  No need for a lawn mower here.

Pseudolarix amabilis Golden larch

Abies lasiocarpa Subalpine fir off of Margaret Eyre’s back deck

Mixing forms, textures, and colors provides a study in contrasts

In addition Margaret Eyre’s place we toured the home of John and Margaret Havlis.  The Havlis’ landscape is quite large – a couple acres – and shows what conifers and a little creativity can accomplish.

Conifer border around the Havlis backyard.  Note the winter deer protection for new specimens.

Recurved needles on Abies koreana ‘Silberlocke’

Microbiota decussata Russian cypress.  Conifers in this part of the garden are set of by hardscaping that imitates a dry creek-bed.

Love in Broom

Recently, Rebecca Finneran, an MSU Extension Educator from the Grand Rapids area sent me a cool photo.  The tree is a large Norway spruce near the Kent country Extension office.

This is a great example of witch’s broom.  Witch’s brooms are growth anomalies that occur on various trees, most commonly conifers,   Brooms can be caused be a variety of factors including diseases, aphids, environmental stress and random mutations.  In some cases the growth defect is only present when the casual agent, say, a pathogen is present.  In others, however, the growth mutation can be propagated by grafting scion wood from the witch’s broom onto a regular rootstock.  In fact, this is the origin of many forms of dwarf and unusual ornamental conifers.  Because of this, brooms are often a prized commodity and ‘Broom hunting’ is an active past-time for conifer enthusiasts such as members of the American Conifer Society.  ACS members that find their first brooms are sometimes referred to as ‘Baby broomers’.  Broom hunters are a focused lot and have been known to screech to a halt on major interstate in their relentless pursuit of conifer conversation pieces.  So keep an eye out for brooms – and broom hunters!

With the late Chub Harper and the ‘Merrill broom’ tree at Hidden Lake Gardens, Tipton, MI

A rose by any other name…

This past week I got to spend three days doing one of my favorite things; talking about conifers.  Wednesday I was a last-minute guest lecturer for a landscape design class and Thursday and Friday I did my ‘Conifers for Connoisseurs’ talk for our MSU Extension ‘Plants of Distinction’ program.  One of my favorite conifers and one I often recommend as a large specimen tree is Alaska yellow-cedar (the name I learned in Mr. Chance’s Botany class at Olympia High School) or Nootka false cypress (the usual common name for the tree in this part of the world).  Notice that I didn’t give a scientific name, like a good garden professor should.  The reason?  I’m not 100% sure what the scientific name for Alaska yellow cedar is any more.


Xanthocyparis nootkatensis at Daisy Hill Farm, DeWitt, MI

Prior to 2000 it would have been easy: Chamaecyparis nootkatensis.   Then a team of international scientists including members of the Kew Royal Botanic Gardens and the Missouri Botanical Garden discovered a rare conifer in northern Vietnam, which was previously unknown to science. The new species was described in a 2002 article by Farjon et al as Xanthocyparis vietnamensis.  A conifer still unknown to science at the end of the 20th Century, that’s pretty cool.  But, in addition to describing and naming the new species, the authors’ also reclassified Chamaecyparis nootkatensis with the new species as Xanthocyparis nootkatensis.  While this news was mildly disappointing to those of us who love the tree and thought Chamaecyparis nootkatensis was about the coolest scientific name ever, the name change was not entirely surprising.  Within the genus Chamaecyparis, nootkatensis was always the proverbial red-headed step-child.  At one point the species had been grouped in the genus Cupressus.  The change to Xanthocyparis also required a change for Leyland cypress, an intergeneric hybrid between Alaska yellow cedar and Monterey cypress (Cupressus macrocarpa).  Under the new nomenclature ×Cupressocyparis leylandii becomes  × Cuprocyparis leylandii. 

Now, as if all this weren’t confusing enough, subsequent work by Damon Little based on molecular markers groups all of the Cupressus species in North America and the two Xanthocyparis species under one genus, Callitropsis.  Little et al’s re-classification and rejoinder by Mill and Farjon (2005) demonstrate the schism which has developed between taxonmists that rely heavily of cladisitcs and molecular tools and those that rely on morphology and evolutionary relationships.  Their debates are far testier than any barbs traded between Linda and the Brothers Horvath.  Check out this link for a taste of the action:


Xanthocyparis nootkatensis at MSU Horticultural Gardens

So what about us poor horticulturists and foresters who just want to know what to call the damn thing?  I suspect the taxonomic battle lines will deepen before anyone offers a peace offering.  And this will extend far beyond Xanthocyparis (syn. Callitropsis).  Get used to seeing lots of synonyms next to scientific names in the future.  Remember when you took your first Botany class and learned we used scientific names to eliminate confusion over common names?  Sigh… Alaska yellow-cedar sounds pretty good to me.

Farjon, A., N.T. Hiep, D.K. Harder, P.K. Loc, and L. Averyonov.  2002.  A new genus and species in Cupressaceae (Coniferales) from northern Vietnam, Xanthocyparis vietnamensis. NOVON 12:179-189.

 Little, D.P., A.E. Schwarzbach, R.P. Adams, and C.-F. Hsieh. 2004. The circumscription and phylogenetic relationships of Callitropsis and the newly described genus Xanthocyparis (Cupressaceae). American Journal of Botany 91(11): 1872-1881

Mill, Robert R. and Farjon, Aljos. 2006. Proposal to conserve the name Xanthocyparis against Callitropsis Oerst. (Cupressaceeae). Taxon 55(1):229-231


And now for something completely different…

From this week’s e-mail file…

“Dear Dr. Cregg:

As I’ve done for many year, this year I harvested my “wild” Christmas  tree from the Huron-Manistee National Forest. I cut the tree at ground level. Soon after I brought it home, it started sprouting new light green clumps of needles at the tips of many branches. Is the tree actually growing? It doesn’t seem possible that it’s still alive, but it seems to be thriving and I hate to toss the tree to the curb if it’s fighting for life. I am tempted to leave it in the tree stand to see what happens….”

Pat M.

Midland, MI


Dear Pat:
The tree is dead, it just doesn’t know it yet.  Depending of the species, some Christmas trees will break bud and begin to grow once they are brought indoors.  The tree is still alive in the sense that its needles are still carrying out photosynthesis and water is still moving up the trunk to the needles.  But since the tree has no roots and no way to produce any new roots, it has no prospect for long-term survival.  The phenomenon you’re observing is common in some spruces and other conifers adapted to cold regions.  Before you cut the tree, the buds were exposed to enough cold to meet their chilling requirement to overcome dormancy – the only thing that keeps trees in wild from growing at this point are cold temperatures.  Once you brought it indoors, the tree ‘thought’ is was spring and started to grow.  If you or a family member want to do a little science project you could keep the cut end in water and see how long the tree lasts.  Eventually, however, the conducting elements at the cut end will begin to plug with resins and the tree won’t be able to move enough water to meet its needs and will expire.

Bert Cregg


O Tannenbaum!

Twas the blog before Christmas…  My last chance to post about Christmas trees for another year.  I’m always surprised when I troll around the web or do interviews how many myths about Christmas trees still abound.  So in the spirit of the season, a little Christmas tree myth-busting.

“Good grief.  I’ve killed it.”

Using a real tree hurts the environment
Here’s a real post from the website:

“Its so not fair to cut down all those baby trees, use them for a few weeks and then toss them by the curb for garbage removal. Everytime, i pass by a house and i see those poor trees just shoved out like that it breaks my heart. they belong in the forest or backyard where they were meant to be, growing old and improving the air and atmosphere. i used to like real Christmas trees but not anymore.”

Yes, Virginia, there are still people out there that think Christmas trees are cut from forests. The U.S Forest Service and some state forestry departments do offer permits to cut Christmas trees but this is a tiny fraction of the trees used in the U.S.  Virtually all Christmas trees sold at tree lots and stores are grown on Christmas tree farms for that purpose.  For each tree cut, growers plant two or three more.   Moreover, many communities have programs for re-cycling Christmas trees into mulch or compost.

Christmas trees are a fire hazard.
The key here is water.  Fresh Christmas trees that are properly watered are not a fire hazard.  Trees that are allowed to dry can be a fire hazard.  These are the ones your local TV station uses for their annual dramatic Christmas tree fire video.

Fire retardant sprays make Christmas trees safer.
Research by Dr. Gary Chastagner, a colleague of Linda’s at WSU-Puyallup, has shown that some fire retardants can actually increase tree moisture loss.  Maintaining tree moisture is the key to making trees safer and improving needle retention.  Making sure the tree stand never dries out is much more important than a fire retardant spray.

Injecting water directly into the stem is the best way to maintain tree moisture content.
This is a case where a little knowledge can be a dangerous thing.  Since water moves up the tree through the xylem elements in the stem, wouldn’t injecting water right into the stem be the best way to water?  That’s the logic behind the Tree I.V.  As the name implies, this device is like an I.V. drip for your tree.  Drill some holes in the trunk, attach some tubes to a jug a water, and voilà, a self-watering tree!  We can thank Gary Chastagner again for busting this myth.  He and some colleagues found that displaying a tree in a regular tree-stand with water maintained higher tree moisture levels that the I.V. technique.

So, if arborists can use trunk injection to apply pesticides and fertilizers to trees, why wouldn’t the Tree I.V. work?  Actually, the tree I.V. does work in the sense that the tree will take up water from the jug.  The problem is that the tree may not take up enough to meet its total water need.  In a normal stand, the entire stem cross section is exposed to water.  With the tree I.V. only a portion of the stem will be translocating water.  Plus, conifers contain resin ducts which clog injection ports.  This is one of the reasons why arborist’s trunk injections don’t work as well as on conifers as they do on most hardwoods.

Bottom-line, keeping your Christmas tree hydrated is the key to retaining needles and keeping the tree safe.  A good rule of thumb is that a stand should hold a quart of water for each inch of tree caliper at the base.  For most trees this means a stand that will hold at least a gallon of water.   Check water in the stand daily and never let the tree go dry.

Have a very merry Christmas!