Does native matter?

We’ve had lots of lively discussion on my post regarding the Mark Davis et al. comment in Nature on natives and exotics. I have been traveling and otherwise occupied and have not had a chance to comment so I feel a little like the kid that kicked the anthill and then ran away. Fortunately, Holly was gracious enough to forego her post today (I promise to return the favor, Holly!) so I can chime back in.

Obviously there are lots of layers to the debate but one of the main items in the discussion is whether there is an inherent ecological advantage in planting natives over exotics.  At this point the focus always seems to shift to herbivory and the question of whether native insects will eat non-native plants.  There are certainly examples each way; some insects are generalists while others are highly specific.  More importantly, however, plants fill many other roles in the environment beyond serving as food for insects.   Moreover, species composition is just one aspect of diversity.  The ecological function of landscape is also determined by how we manage other factors such as structural diversity and age class distributions.  In his book “Bringing Nature Home” Doug Tallamy shows a picture of a bland, sprawling suburban landscape ( p. 24) and notes “this highly simplified community is made up of a few species of alien ornamental plants that provide neither food nor shelter for wildlife.”  OK, I’ll buy that.  But would the situation change if the blue grass was changed to a native grass kept mowed to 2” and the two widely spaced shade trees were changed to natives?  Doubtful.   The structural complexity; that is, the number and arrangement of grasses, annuals, shrubs, and trees, is likely a bigger driver of ecosystem function than whether the plants are native or exotic.

In his thoughtful comments on the blog post Vincent Vizachero sums up, “I stand by my view that the general heuristic of favoring native plants over alien plants is better than the alternative of not caring about origin at all.”   I can buy that as well, but with the caveat that other factors are equal.  The rub, of course, is that other factors are rarely equal.  And I suppose this is where the pragmatic approach discussed by Davis et al.  resonates with me.  In my position I do a lot of programming on trees for urban and community forests.  I go through a list of criteria to consider for tree selection.  Here are some of the key factors I usually discuss:

Adaptation There is no argument that there are well-documented environmental, economic and social benefits to trees in urban and suburban areas.   But in order to fulfill these roles trees must be able to survive where they are planted.  This means being adapted to abiotic and biotic environmental conditions which are often adverse.  In this region of the country there are some native trees that fit the ‘tough trees for tough places’ bill, such as swamp white oak, bur oak, and honey locust.  Many other natives, especially understory species, are much more difficult to site.

This street planting in Lansing alternated green ash and Norway maple.  

Available space This seems like a no-brainer, but it’s amazing how often this gets overlooked and we end up with too much tree and too little space.  Again, we have some great small native trees; Carpinus, redbud, striped maple.  But these can be limited in their site adaptability.

Ash stumps

Diversity  In Michigan some communities have lost 30% of their tree cover to the emerald ash borer.  Have we learned our lesson about improving species diversity?  Not really.  But we need to keep trying.  Exotic pests are here and here to stay.  Does anyone believe that global trade will decrease in the near future?  Does anyone believe that there will be quantum leap in our ability to detect and intercept hitch-hiking pests?  In order to continue to accrue the benefits of urban and community forests we need to continue to diversify our portfolio; this includes a mix of natives and exotics.  I doubt there will ever be sufficient data to prove one way other, but it seems reasonable to me that an urban and community forest balanced among 20-25 native and exotic species will be better able to withstand the slings and arrows of weather and pests better than one made up of 8-10 natives.

Getting to the root of the problem

After getting off to a cool and soggy start, summer has come with a vengeance to Michigan, with heat indices expected to push 100 degrees by Wednesday.  Along with warmer temperatures, summer also means our research season is getting into full swing as well.  One of our biggest efforts these days involves our project to look at pre-plant storage and handling on shade tree liners.


As many GP blog readers are aware, emerald ash borer (EAB) has dominated the conversation regarding shade trees in the Midwest for the past 6-8 years.  Ashes made up 20 to 30% of the shade tree cover in many urban and community forests, so their loss has been devastating.  A major thrust of our extension programming during this time is to promote a wide range of ash alternative to increase species diversity.  One of the challenges we find in making this pitch is that many of the species we recommend (oaks, hackberry, baldcypress) are trees that nurseries often find difficult to grow from standard bare-root liners.


My graduate student, Dana Ellison, is in the second year of a project to look at some of the practices that growers use on the difficult to transplant species and some of the underlying causes of poor transplanting.  Dana is looking at a variety of attributes including plant water relations and carbohydrate status, but the order of business these days is roots.  Specifically we’re evaluating root growth potential of oak, baldcypress, and hackberry.  We’ve also included white ash, which transplant easily, as a positive control.

Graduate research assistants Dana Ellison (right) and Brent Crain (left) and undergraduate assistant Arriana Wilcox (center) pot up shade trees for root growth potential testing.

Root growth potential (RGP) is a common parameter in evaluating quality of reforestation seedlings but is measured less often on larger liner material.  The logic is pretty straightforward; a plant’s ability to initiate root growth after plating and re-establish root-soil contact is one of the biggest determinants of its ability to survive and grow.  A variety of systems have been used to evaluate RGP for seedlings – most involve growing seedlings for a set time (3 weeks is standard) in an aeroponic system and then counting or measuring new root growth.

Growing the trees in pea gravel makes it easy to get a look at new roots.

For Dana’s shade tree liners (5’-6’ whips) we’ve adapted a system based on the Missouri gravel bed system (which I first got to see in person at Jeff’s research nursery in Minnesota – thanks Jeff!).  Dana and her helpers pot the trees up in pea gravel in 25-gallon containers.  The trees are grown on for three weeks in a greenhouse while the roots are kept moist with spray stakes operated by a mist system timer.  After three weeks, we dump out the gravel, wash the root systems, and carefully count the number of new, white root tips.

Dana washing roots.

So what have we learned?  Well, the work is still on-going but some trends have emerged.  Baldcypress may experience some transplant issues but they don’t appear to be related to producing roots.  We had several baldcypress trees that produced 400 or more new roots during the RGP test – and, yes, we counted them all!  Red oak and northern pin oak, on the other hand, are very slow to put out new roots.  For hackberry trees, our other measurements suggest their transplanting issues may be related to their inability to re-hydrate after lifting, storage and transport.  These insights should help us provide some guidelines to growers to help them produce a wide pallet of trees for the landscape market and increase species diversity in the wake of EAB.

Counting roots.  Almost as much fun as it sounds…

The defending champion baldcypress: 614 new roots.

Mortal Kombat – garden version

Soil solarization is regarded as an environmentally friendly alternative to pesticides for controlling nematodes, weeds and disease.  Sheets of plastic (generally clear) are spread over the ground and solar energy heats the soil underneath to temperatures as high as 55C (or 131F).  Since the soil environment is usually insulated from temperature extremes, the organisms that live there are unlikely to be resistant to heat stress.

This is a practice best suited to agricultural production, where monocultures of plants have attracted their specific diseases and pests.  Decades of research have shown success in controlling pests in greenhouses, nurseries, and fields.  But there’s a down side to this chemical-free means of pest control.

It shouldn’t be surprising that beneficial soil organisms, in addition to pests and pathogens, are killed by solarization.  Studies have found that soil solarization wipes out native mycorrhizal fungi and nitrogen-fixing bacteria.  One expects that other beneficial microbes, predacious insects, and parasitoids living in the soil (but so far unstudied) would be eliminated as well.

This may be an acceptable loss to those who are producing crops; soil can be reinoculated with mycorrhizal fungi, for example.  But for those of us caring for our own gardens and landscapes, this is literally overkill.  (And consider that most of us probably have trees and shrubs whose fine roots extend over our entire property.)

So this spring, instead of solarizing your soil, consider some less drastic measures of pest and disease control. Minimize soil disruption to preserve populations of desirable microbes. Plant polycultures (more than one species) in your vegetable garden, or at least practice crop rotation.  Protect and nourish vegetable gardens with compost.  Use coarse organic mulches, which provide habitat for beneficial insects and spiders, in landscaped areas.  Above all, try to treat your soil as the living ecosystem it is, rather than a war zone.

Off-label Use of a Chicken*


[Extremely] Preliminary research results from the University of Maryland indicate
chickens may be of interest in the fight against Halyomorpha halys, the brown
marmorated stink bug. 

There are good stink bugs and bad stink bugs. The brown marmorated stink bug is a bad one. A relatively new introduced pest, it is piercing, sucking, and generally ruining vegetable and fruit crops (as well as some ornamentals) across a good part of the U.S.  There are apparently few natural predators for this imported species and they reproduce like mad, thus the potential for this to become a very serious economic issue. USDA funding has appeared, and scientists are working against the clock on every angle of the problem.

Dr. Stanton Gill, Extension Specialist in IPM for Nurseries and Greenhouses at the UM Central Maryland Research and Education Center, is among them. He is not only a great entomologist, but a total hoot, just like several other bug people I know.  He’s doing plenty of conventional research as well as loads of critical Extension service spread out over several states. As an orchard and nursery owner, he also has a personal stake in the issue.

I had the pleasure of hearing about Dr. Gill’s latest work at a recent nursery association meeting. He related the severity of the problem as well as several stink bug-related research projects he’s involved with, but the one that really caught my attention was his work with chickens.

On a tip from a gardener/hen owner, Dr. Gill decided to explore further. In a nutshell: the stink bomb hidden in the thorax of Halyomopha species is a terrific defense mechanism against bird and reptile predators. But chickens seem to be immune (and unconcerned about their breath). Actually, not a big surprise – I’ve caught my hens eating some pretty amazing/disgusting things.  His preliminary study consisted of a few borrowed hens in a couple of nice little fresh-air pens, free to scratch about. A request to some battle-weary local gardeners yielded tupperware containers full of brown marmorated stink bugs. Through some feeding trials, he found… a hen’s capacity for stink bugs knows no bounds.

The hens had access to their regular feed, but gobbled up all the stink bugs offered. I can’t recall the exact quantity, but it was A LOT.

Stink – it’s what’s for dinner.
Action photo courtesy of Dr. Stanton Gill, University of Maryland

The hens would only go for the stink bugs if they were active.  Dr. G. put some in the freezer (stink bugs, that is), rendering them immobile, and the girls turned their beaks up. Once thawed and moving (!!!), they became dinner.

Finally, he worked with a food scientist to answer what should now be a burning question – did the eggs taste funny?  Blind taste tests found that participants preferred the eggs produced by the stink bug-eating hens versus controls. I believe further studies may be in the works, as well as some publications relating his findings.

* Ha, ha, I kid!!! This post is neither an endorsement nor recommendation of the research described within. There is no MSDS available. No REI. No PPE guidelines. No EPA approval. No acronyms at all, actually. You’re on your own.

An Early Valentine’s Story

In honor of Valentine’s day I have a story about love and betrayal to share….OK, maybe not….perhaps something more along the lines of branches and ants.  Same difference right?

There was once a tree that was much loved.  It was planted in a cute little corner of a street next to a historic building and was well cared for by its owners. Its many limbs rose to the sky in a seething mass which made the tree look vigorous and robust…and those who planted the tree were very happy.

Over time, however, the people who planted the tree neglected it.  The street where it was originally planted changed from a bustling center for traffic to a lonely, out-of-the-way road.  As it was ignored its branches grew together and made a mess — and nobody noticed this mess — except for a little horticulturist who had to walk by the tree every day on his way into work.

The little horticulturist was fascinated by the tree.  Not because the tree was a particularly fine specimen, no, that wasn’t it at all.  Instead the little horticulturist was fascinated by the tree because its limbs grew together so closely that they actually appeared to be grafting with one another, something that the little horticulturist would often spend hours contemplating (what can the little horticulturist say — sometimes he liked to avoid real work).

Two limbs apparently grafted together!

Then one day something terrible happened.  An evil green insect invaded the street where the tree lived, and all of the ash trees on that street had to be cut down.  Even though the tree couldn’t be infested by the insect (it was a hackberry), it was still on the list.  The little horticulturist pleaded with the groundskeepers to keep the tree, but orders were orders and the tree had to go.

But unbeknownst to the groundskeepers the little horticulturist knew one of the people cutting down the tree and asked the tree cutter to save him some of the trees limbs where they appeared to be grafted together.  And the tree cutter did, and delivered them to the little horticulturist.

But alas!  The grafts that the little horticulturist had seen were not truly grafts at all!  They were rotted out sections of trunk which had grown around each other!  The little horticulturist was crestfallen!  How could this be?  He left the decaying limbs in his office as he considered what to do next.

Hmmm…There’s no graft after all –what a mess!

Days stretched into weeks and the limbs continued to sit in the little horticulturists office.  And then, one day, from the depths of the limbs sprouted new life!  Winged carpenter ants flew around the room and into neighboring rooms!  Colleagues shouted curses and obscenities!  Graduate students were afraid to use the drinking fountain because of the masses of ants which alighted there!  The custodians took to wearing dust masks!  And, despite incessant pleading by almost everyone, the little horticulturist would not part with the limbs because he wanted to have props whenever he told the story of the day the ants took over the 4th floor.

The moral of this story is that you shouldn’t hold onto things once you figure out that they’re worthless.

Scrambling for Answers

Yesterday a good friend of mine who works for a well respected tree company in town asked me whether I would be willing to talk about  tree conservation as it relates to the emerald ash borer.  Specifically he wanted me to make people aware of a statement produced by a group called the Coalition for Urban Ash Tree Conservation which you can find here which was produced by a number of well respected industry people and academics.  This statement basically says that we shouldn’t cut down all of our ash out of fear of the emerald ash borer but that we should, instead, treat some with various insecticides to conserve our ash.

I don’t have any major disagreement with the article, but it’s important to remember that every situation is different and that, while chemical treaments might be appropriate for one ash, another should hit the chipper.  As the emerald ash borer moves across the country we’ve got to assess what our ash are worth to us and decide when and where it’s appropriate to save them.  This is an extremely daunting task without easy answers.  The statement by the Coalition for Urban Ash Tree Conservation is good and very appropriate, but what would be even better is a guide to help people decide whether to leave trees alone, to cut them down, or to treat including all of the costs and consequences.

UPDATE:  As you might have expected, there is already a cost calculator out there — I just wasn’t aware of it.  Fortunately Katie was and left details in the comments section.  If you are interested in a calculation to figure out the cost of treating vs. removing ash go here and then click on EAB cost calculator — it’s on the left hand side.  It’s a very nice little tool!

Bounce – it’s not just a fabric softening sheet…

…it’s an Integrated Pest Management tool!

[Note added after-the-fact: this was a  tongue-in-cheek bit of  hyperbole – kind of like “it’s not just a Job, it’s an Adventure.” Did not mean to imply that it actually IS an IPM tool. Very badly worded. Hence the beating I took in the comments. Live and learn.]

Fungus gnats (Bradysia spp.) are a pain in the bottom for commercial greenhouse growers. The adults are more of a nuisance than anything else –it just looks bad when a customer picks up your 6” pot of pansies and a bunch of little black gnats take flight.  It’s the larvae that are problematic. Adult females lay the eggs in especially damp growing media, and the newly-hatched larvae feed on the roots. There’s both direct damage and also speculation of easier infection of root-borne pathogens, of which there are plenty. 

Fungus gnat larvae, just making a living…

Standard control measures include insecticide drenches, biological controls including a specific strain of Bt (Bacillus thuringiensis – sold as GnatrolTM), nematodes, etc.  One of the easiest control measures is the one I teach my students: to not over-water, i.e. “grow dry”. But that can be difficult in a big greenhouse range with many different-sized containers, all which drain/dry out at different rates. Propagation houses also have high humidity levels and have to stay moist for rooting/germination purposes and are thus favored by fungus gnats.

Entomologist Dr. Raymond Cloyd of Kansas State University and his group were intrigued by Master Gardener anecdotes of dryer sheets repelling mosquitoes, though no research had been done. Could your common Bounce sheet also repel other pests? And, to take it a step further, what, exactly, repels them?  The answers are “yes” and “lots of volatile compounds.”

Their study was published last month in the journal HortScience. Honestly, I’ve never seen descriptors like “controls static cling” and “gives clothes a fresh scent” in a Horticulture journal. Hee! Plus the researchers made it clear this experiment specifically used Bounce Original Outdoor FreshTM. Still kind of humorous, but really good science and the part that’s usually overlooked in the translation to a News Story. Do NOT extrapolate results to include Bounce Spring Fresh, Fresh Linen, and certainly not Downy or Snuggle brands. 

The study had a simple design, releasing lab gnats (ha!) into a  many-chambered container and observing to which chamber the gnats gravitated to (or away from).  There were five different variations on this theme, including an alluringly soggy media sample; when the sample of fabric softener sheet was introduced, they stayed away in droves. All five experiments showed a fairly drastic aversion to the sheet. To determine what was fending off the gnats, they did a steam extraction on sheet samples and ran the condensate through a gas chromatograph – mass spectrometer to measure the volatiles.

Figure from Bounce® Fabric Softener Dryer Sheets Repel Fungus Gnat, Bradysia sp. nr. coprophila (Diptera: Sciaridae), Adults. Raymond A. Cloyd, Karen A. Marley, Richard A. Larson, and Bari Arieli, HortScience Dec 1 2010: 1830–1833

Well, there you have it. Linalool is a monoterpene alcohol found in lavender, basil, and coriander, and is known to be toxic to mites and insects.  Citronello is another monoterpene and lends lemony-freshness to lemon balm, pennyroyal, and rose geranium and has short-term “repellent activity against mosquitoes.”  Benzyl acetate, though not specifically mentioned in the results, is another natural fragrance compound, found in jasmine – and is also an industrial-strength solvent. One man’s solvent is another man’s perfume. Or fabric softener. I bet their lab smelled GREAT, by the way.


Saving your ash

My earlier post regarding plans to replace the monoculture of ash trees at the Gateway Arch Monument in St. Louis, MO with a monoculture of Lindens prompted a question about options for treating ash trees for emerald ash borer.  This is a complex topic so I wanted make sure I had time and space to respond completely.


First, the best and most current source of information regarding treatments for EAB is the Multi-state bulletin “Insecticide Options for Protecting Ash Trees from Emerald Ash Borer” which is available as a full-color .pdf on the website.  Anyone who lives in or near EAB-affected areas and is considering treating their ash trees should take the time to download and read this bulletin.


Here are some key points to consider if you want to save you ash:

It is possible to protect ash trees from EAB with insecticides.  There are several examples in and around the original core infestation area in Detroit where arborists have successfully protected trees since EAB first was identified in 2002.  There are two general options; protective cover sprays and systemic applications.  For most trees, protective cover applications will require professional application with specialized high-pressure spray equipment.  Most systemic application will also need to be applied by professional applicators, except for small trees that can be treated with soil drenches of systemic insecticide.  To date, the most effective systemic product is emamectin benzoate, sold under the trade name TREE-äge.  In various tests, emamectin has shown the highest level of control among products tested and is also the only product that consistently provides more than one year of control.  Imidacloprid is also effective as a systemic but will need to be re-applied annually for the best level of control.


The likelihood of successfully treating an ash tree declines rapidly once trees begin to show noticeable crown-die-back.  In certain cases, researchers have been able to save EAB-infested trees showing some crown die-back, but once 50% of the crown is affected the tree is likely a goner.


Once started, treatments will need to continue in perpetuity.  To me, this is the biggest factor homeowners need to consider if they’re thinking about treating their ash trees.  To the best of our knowledge, EAB is here to stay.  EAB populations may begin to decline once most of the ash trees in a region have been wiped out, but trees in woodlots and forests that have been killed will continue to sprout, providing host material to maintain an endemic population of beetles for the foreseeable future.  Systemic applications can provide control but the products will need to be re-applied every year (imidacloprid) or every other year (emamectin) to be effective.


Effectively treating trees larger than 4” in diameter will require applications by a certified pesticide applicator and may cost several hundred dollars per tree.  Homeowners need to carefully consider the cost of on-going treatments versus removal and replacement.


Mention of trade names does not imply in endorsement.  Read and follow label directions when applying pesticides.

Are Fertilizer and Insecticide Spikes a Good Idea?

One of the products that I often hear gardeners raving about are their fertilizer / pesticide combination spikes which are supposed to not only feed your plants, but also kill all of the insects which attack them.  I, personally, have not used these products, but I’m generally the kind of person who says “If it works for you then keep using it”.  Still, these spikes bug me a little.  Here’s why.

First of all I should point out that I’m not opposed to fertilizer spikes by themselves.  I’m a little concerned that fertilizer should be spread out instead of concentrated in one place, but still, I don’t consider them that bad.  The insecticides used for these spikes is where I have the problem.  Once upon a time these spikes were made with a chemical called disulfoton (aka disyston) which is bad news.  It’s a water soluble chemical which is highly toxic to people.  If you have an old package of fertilizer / insecticide spikes around there’s a good chance they were made with this chemical.  Do yourself a favor and get rid of them.  This stuff is really toxic and not to be messed with.  On the other hand, if you’ve purchased fertilizer / insecticide spikes recently, then the active insecticide in those spikes is probably imidacloprid.  Imidacloprid is a mixed bag when it comes to safety.  It’s not nealy as toxic as disulfoton, but it’s not non-toxic.  It has been banned in Europe for a variety of reasons, the most important of which seems to be that it was implicated in the collapse of bee hives (imidacloprid is systemic insecticide so it will get into a plants pollen where honey bees could eat it).  At this point it hasn’t been ruled out as having something to do with hive collapse here in the states — though if it does have a role it does not seem to act alone.  It can also affect other beneficial insects who feed on pollen.  Additionally, it has been known to control some pests while allowing mites to go crazy — in fact, it may even increase the rate of mite egg laying.

But imidacloprid is an effective insecticide which works against a wide range of insects which you that you might find on your plants.  It is much safer than many of the older systemic insecticides, and it isn’t readily translocated to fruits (a problem that many people are concerned about with systemic insecticides is the movement of these insecticides into the fruit itself where it can’t be washed off — Imidacloprid is translocated to fruits –just not that much — it moves in the xylem and fruit takes up mostly phloem).

So these spikes are one of those things that I’m wary of.  Not to say you shouldn’t use them, but be aware of what they are and what they could do before you buy them.