The winter of our discontent

I was in the field today at our Southwest Michigan Research and Extension Center (SWMREC) so just a quick post and a couple of pictures.  Today is the last official day of winter but you’d never know to look outside. Our current temperature in East Lansing is 78 deg. F.  Our late winter warm up has officially reached historic proportions as we have blown by 1945 as the warmest winter in record in lower Michigan.  To give you an idea of how messed up things are the current temperature in Minneapolis, MN (77 deg.) is 21 deg. warmer than Los Angeles (56 deg.). 

While I hate the be the messenger of doom as Chicagoans enjoy fun and frolic at the beach, for many segments of horticulture what we’re watching unfold is a slow motion disaster.  Phenological development (bud-break, flowering etc.) is currently running almost a full month ahead.  Many important fruit crops such as plums and peaches have started to flower and the rest aren’t far behind.  Based on long-term records it is virtually certain that we will have several hard freezes before the weather warms up for good, meaning that many of these crops will be severely damaged if not destroyed entirely. So, if you’re in the Midwest or East, make the best of the good weather but recognize all good things must come to an end…


Plum crazy.  Plum blossoms at MSU SMREC, March 19, 2012


Just peachy.  Peach tree in bloom. MSU SWMREC, March 19, 2012.

A Good Potting Soil

On this blog we get mad at lots of things.  Sure, anger is fun, but sometimes you’ve got to suck it up and say something nice for a change.  So today I thought I’d point out a product that, while it comes from a company that I’ve had issues with in the past, is, itself, a good product.  I like Miracle-Gro Moisture Control potting mix.  The reason is that it utilizes coconut coir, a waste product from coconuts which holds lots of water and which can still maintain good aeration.  That means a reduced amount of peat.  I also like that the fertility present in this product (so you don’t need to fertilize right after you plant) is 3-1-2 which is appropriate for most situations.  Now, could you mix up you own coir potting mix more cheaply?  Sure, if you can find it.  You could also fertilize with a renewable organic fertilizer.  Still, I think Miracle-Gro got this one right.

The Cold Truth

Last week I decided to continue my discussion on cold hardiness and so now, of course, temperatures are forecast in the mid-70’s for this week.  Oh well, I’m still convinced we’ve got one more blast of winter to go and some of this will still matter to someone.

One of the questions posed in response to last week’s post was how much cold hardiness changes during the winter.  Before I get into that, it’s good to review how cold hardiness can be quantified.  Cold hardiness is essentially how much cold a plant can withstand before it suffers damage.  There are two common ways by which this can be measured.  The simplest and most straightforward method is through a whole plant (or whole shoot) freeze test.  In this test, entire plants, usually seedlings, are placed in freezer that is programmed to drop the temperature progressively colder, say from 3 deg C to -36 deg. C

At set intervals, often 3 deg. C, a group of plants are removed.  The plants are allowed to slowly thaw and are then examined for needle damage or bud kill.  At the warmest temperatures, plants are undamaged.  As we examine plants subjected to colder temperatures, we’ll begin to find some with damage.  Eventually we’ll find a temperature where all the plants are damaged.  When we plot the percent of damaged plants versus temperature we can identify an LT50, or lethal threshold where 50% of plants are damaged.


Examples of determining bud damage during whole shoot freeze tests.

The second common assay for cold hardiness is termed Freeze-induced electrolyte leakage or FIEL.  FIEL testing is similar to the whole plant freeze test except that instead of freezing the entire plant or shoot, just a small portion of tissue, such as a conifer needle segment is needed.  The FIEL test is based on the fact that plants can withstand inter-cellular ice (ice between cells) but not intra-cellular ice (ice within cells).  When intra-cellular ice forms it disrupts the cell membranes and cell contents are released into solution.  The amount of leakage of cell contents into solution can be easily measured using a standard conductivity meter.  Again, we can estimate an LT50 by plotting the amount of damage versus exposure temperature.

By assessing cold hardiness periodically through the winter, we can assess changes in hardiness associated with acclimation and de-acclimation processes.  A classic study by Karen Burr and her colleagues demonstrates how quickly acclimation can change.  In their study they tracked cold hardiness of conifer seedlings that we exposed to acclimating conditions (short days and progressively colder temps) and then de-acclimating conditions (longer days and warming temps).  The resulting chart demonstrates how dynamic cold hardiness can be.  When we describe plans based on Hardiness zone we’re talking about their maximum hardiness or the temps they can stand in the mid-winter period.  But note how quickly the lethal temperature rises during de-acclimation.
Seasonal trend in phases of cold hardiness: Acclimation, Maximum hardiness, and De-acclimation

Typically, our most common winter injury problems occur during the de-acclimation phase as temps warm and hardiness is lost.  We saw a dramatic example of this several years ago in western Michigan when an early March warm-up with temperatures in the 50’s F was followed by nights with temps as low a -5 deg.  This resulted in widespread bud-kill in conifer plantations.  With a week of highs in the 60’s and 70’s forecast, it’s easy to see why our current warm-up has everyone nervous.

Maximum and minimum temperatures from a west Michigan weather station

Should I trust Dr. Earth?

Most of us were taught from an early age to trust doctors (I mean the medical kind).  They’re supposed to be smart, committed, and loving, and most of the doctors I’ve had over my life have fit that mold.  And Earth, what an awesome name!  It makes me think of dark, warm, rich soil in the spring.  Damn it makes me feel good!  So it’s no wonder that some clever marketer thought up the name Dr. Earth and slapped it on a bunch of organic products, because hey, if you can’t trust Dr. Earth who can you trust?  When I see a Dr. Earth package I want to buy it!  I mean look at it:

How can you not trust this guy?  But as most wise shoppers have learned over the years, whenever you purchase a product you should look at the ingredients to see what you’re buying.  This product includes Probiotics — microbes which are probably dead when you buy the fertilizer — or which may not even be compatible with your soil.  It is a “balanced” fertilizer meaning it has equal parts nitrogen, phosphorus and potassium — which means too much phosphorus and potassium.  And finally, while it does have a number of good renewable ingredients, it also contains bat guano and rock phosphate, two ingredients which are non-renewable and which damage the earth when they are mined.

You can’t judge a book by it’s cover, or, apparently, a fertilizer, by the cute farmer-looking guy on the front of the package.

Hot enough for ya?!

Ok, ‘Hot’ might not be exactly the right word, but winter in the Midwest has certainly been warmer than average this year.  I did a little trolling around on Michigan State University’s Automated Weather Network website, which has been logging temperatures and other weather variables around the state for the past 15 years and compared our current winter here in East Lansing to recent years.  Since the middle of December our average daily temperatures are 5.2 deg. F above the previous 15-year mean.  The departure from the 15-year mean is even greater (+5.6 deg. F) when we look at minimum temperatures. 


15-year average Minimum daily temperature and Current-winter daily minimum for East Lansing, MI.

Minimum temperatures are especially important when discussing winter injury to landscape plants since extreme low temps (and the conditions immediately preceding them) are often responsible for many of our winter injury problems.  With a generally mild winter and only a few, brief temperature dips below average, one might expect that we will see few winter-related plant problems this spring.  However, prolonged exposure to temperatures above average means that plants are beginning to deharden early.  We see several signs of this already; such as witch-hazels blooming in protected locations and sap in maple trees running 2-3 weeks ahead of normal http://www.michiganradio.org/post/michigan-maple-syrup-producers-say-season-extra-early-year


February 28, 2012. Witch-hazel in bloom on MSU campus.

While other trees and shrubs may not provide the same outward signs, they are progressively becoming less cold-hardy by the day.  Unfortunately, temperatures, like the stock market, rarely move in a straight line. Here in mid-Michigan, temperatures in the single digits are possible throughout the month of March.  Given the preceding mild conditions, a sudden, severe cold snap still holds the potential to cause considerable damage to developing buds on trees and shrubs.  This type of late from damage may be evidenced by shoot die-back, bud-kill or death of newly-emerging shoots.  As always with winter injury, the final result won’t be known until late May or early June. 

Moving from tree planting to tree performance

I ‘like’ American Forests page on Facebook so I receive their periodic updates.  One item that caught my eye recently was a profile article on Dr. Greg McPherson, who is an urban forestry researcher with the USDA Forest Service in Davis, CA.  Even if you don’t recognize the name, if you have even seen any statistics on the economic and environmental benefits of trees in cities (energy conservation, carbon sequestration, etc), they probably cited information for McPhereon’s studies, either directly on indirectly,

http://www.americanforests.org/magazine/article/forest-frontiers-greg-mcpherson/

What really made me say “Amen, brother!” in the American Forest piece was McPherson’s response to the question, “What’s the biggest issue in urban forestry today?”  His reply, “Moving from the tree-planting paradigm to the tree-performance paradigm.”  Let’s face it, tree planting, for want of a better term, is sexy.  It’s relatively easy to raise money or get politicians to show up for a tree planting event and throw a few scoops of dirt with a ceremonial silver-plated shovel while the local media cameras are clicking.  

Image: Stephen Simpson/London News Pictures

But who is going to get excited about maintenance pruning? Or developing workable tree ordinances?  Or a pest management program?

Image: Susan Lesch

I’ve participated in various tree planting programs and it always gives me mixed emotions to hand out tree seedlings to second graders.  I’m glad they’re excited about getting a tree but also realize most of the seedlings that those 7-year-olds are running with will have the same lifespan as a goldfish that comes home in a plastic bag from the county fair.  Does this mean we should ban tree giveaways or planting events?  Of course not. Even if only a few seedlings survive the grubby hands of second-graders, that’s a plus and building their awareness of trees and their environment is the bigger issue.  But we also need to build public awareness of what it takes to maintain the urban forest and accrue all those benefits on the long term.  And most of those activities don’t make good photo ops or video clips for the local TV news.

In some places, we’re starting to get the message.  Here in Michigan our Department of Natural Resources awards Community Forestry grants.  The program will fund various activities but many grants are for tree planting.  If the application is for tree planting, the applicant must include a description of the maintenance practices that will be used to ensure the long-term success of the planting – forcing applicants to think about what happens after the trees are planted.  In addition the program also requires that applicants plant a diversity of species to help reduce issues with monocultures.  Small steps, but the ones we need to take to move from the tree planting paradigm to the tree performance paradigm. 

Going Overboard with Paul Tukey

According to a post by Paul Tukey on safelawns.blog, a recent French study which was published in the Journal of Applied Toxicology shows that corn which has been genetically modified to produce the caterpillar toxin Bt is poisonous to humans.  Furthermore, so is roundup.

Ladies and Gentlemen, we’re screwed.

The rapture is coming.  The true believers who shun conventionally produced food and eat only organic, non-GMO will be saved.  Those who don’t, well, they’re all as good as dead so don’t even bother worrying about ‘em.  Brothers and Sisters, change your ways now while there’s still time!

The end will come, not in the form of fire or water, but instead kidney failure and it will come as punishment for playing with Nature.  By messing around with that which Nature has wrought we have inadvertently created a subtle beast that now lies quietly in our bloodstream poised to destroy us.  We are the architects of our own doom and can only hope that those who survive the destruction mend their ways to bring this world back to its GMO and pesticide-free ways.  It’s our only hope.  

OK, the above statement is more than a little over the top.  Hopefully you realized that as you were reading it.  Here’s the real story.  Let me start with Paul Tukey.

I’ve read a lot of what Paul Tukey has written.  He’s a guy who’s very concerned about the amount of poison that we spray on our crops and our lawns and, to be honest, I admire his resolve, and I agree that we overuse pesticides – and to go a step further it’s people like him who are going to get people excited about reducing pesticide use and are going to make a difference in the backyards of America.    

BUT (you knew there would be a but didn’t you?) he has a habit of over-interpreting what the studies say and/or passing along information that does the same.  Usually it’s not too bad.  For example, this article about Round-up is a bit over the top and is based more on the beliefs of one scientist who is considered an extremist rather than on our best scientific data, but at least it acknowledges the fact it might be wrong.  It’s the kind of article that I don’t like, but not one I’m going to get up in arms about because then I’d be constantly up in arms and probably end up suffering from chronic migraines – there’s just too many articles like this for me to worry about all of them.

The article that I began this post discussing is different because it says, and I quote “genetically modified corn containing the genes for Bt (Bacillus thuringiensis) is toxic to humans” and then goes on to say the same thing about Round-up.  The implication is that the study which was conducted shows without the shadow of a doubt that we’re killing ourselves by eating genetically modified crops which have the Bt toxin and/or have Round-up used around them – at least I think that’s the implication.  If any of you think I read it wrong please let me know.

The idea that this study shows that we’re hurting ourselves with genetically modified crops is ridiculous (please be aware that I’m talking about this particular study — there certainly could be others in the future that change my mind).  Why you ask?  Let me count the ways.

  1. We eat Bacillus thuringiensis all the time.  It’s a naturally occurring bacterium which is often present in food and is cultured as an organic pesticide which is likely to be present at some concentration in organically produced crops sprayed with it.  If you think that avoiding genetically modified foods will keep you away from it you’re sadly mistaken.
  2. This study tested the effects of Bt and Round-up on a strain of kidney cells.  Hardly any Bt and Round-up gets to kidney cells even if you eat or drink them – there are just too many barriers to cross before reaching the blood stream (But it is important to note that some certainly does – just very, very little – One article I found showed a level of about 0.2 nanograms Bt/milliliter blood and about 75 nanograms Round-up/milliliter blood in a population in Canada). 
  3. This study artificially placed Bt and Round-up in with kidney cells in a test tube.  Obviously nothing like a natural environment.  Try the same thing with coffee or dish soap at the same concentration and I bet you’ll see worse damage to the cells.         
  4. Just to get picky, kidney cell line 293 was used.  Look it up on Wikipedia (look up HEK 293) this IS NOT an appropriate cell line to be testing poisons on.

Long story short — the article cited really doesn’t reveal much abo
ut how safe or dangerous genetically modified crops are.

Milky Spore

There are a lot of great products out there for controlling insect pests without using pesticides.  Some of the best include insect diseases or predators which will attack the pest and not beneficial.  For example, there are wasps that kill mealybugs and nematodes that attack grubs.  Both of these products are pretty effective.  That said there are also some products that just don’t work that well.  One of them is known as milky spore disease.

Milky spore disease is a bacteria that infects a variety of different scarab beetles – of which the Japanese beetle is one.  It isn’t a disease that we imported from Japan – it’s actually one that was found here.  Because this disease affects the Japanese beetle and it isn’t a pesticide per se people get very excited about it.  The problem is that it just doesn’t work that well.  Sure, it will offer some control, but not much.  Probably somewhere less than 20%.  Furthermore, most people use it in hopes of reducing their adult beetle population, but adult beetles come from all over, perhaps even miles away, so killing the beetles in your soil doesn’t in any way guarantee that you’ll be controlling the adult beetles eating your roses.

Now if you want to encourage your township to try milky spore disease that might work.  Spread over larger areas milky spore will have more of an effect for obvious reasons.  But placed on one yard, it’s just not going to do that much.

Why don’t landscape trees respond to fertilization?

As part of my ‘other duties as assigned’, I have taken on an assignment to develop fertilizer prescriptions for landscape trees and shrubs based on soil samples submitted by homeowners to the MSU soils lab.  This has gotten me immersed in two sets of conflicting literature. 

On one hand is a raft of extension bulletins and ISA guidelines on tree fertilization, which typically suggest adding 2-4 lbs of nitrogen (N) per 1,000 sq ft of ground area – in some cases up to 6 lbs of N per 1,000 sq ft (Rose 1999).  To put that last number in perspective, that works out to 262 lbs of N per acre.  A typical recommendation for corn in Ohio is 150 lbs of N per acre.  Landscape trees need more fertilizer than a field of corn?

On the other side are numerous landscape studies, and even some nursery field studies, that suggest landscape trees simply don’t respond to fertilization (Day and Harris, 2007; Ferrini and Baietto, 2006; Harris et al., 2008; Robbins, 2006; Werner and Jull, 2009). 

So, what gives?  I mean, we know trees need nitrogen to make proteins, enzymes, chlorophyll, and all that good stuff.  We rake up leaves and haul them away each fall; short circuiting the natural nutrient cycle.  Urban trees should be starving for nutrients and begging to be fed, yet don’t grow any better when we fertilize them?  There are likely several factors at work.  First, many of the widely circulated recommendations are based, at least in part, on rates that might be applied in production forestry or nurseries where maximizing growth is a primary objective.  Also, as Dan Struve (2002) noted in his review, some recommendations were based on poorly designed studies.   Or, as Dan Herms (2002) hypothesized, trees may be allocating more resources to defensive compounds. 

Another answer may be found in some of the papers cited above.  In many cases, foliar N levels of the control (unfertilized) trees were already in sufficiency ranges.  In other words, even without fertilizer the trees had enough nutrients.  Part of this is a recent emphasis on the question of fertilizing at transplanting.  Trees coming in from a nursery are likely to be pretty jacked up with fertilizer – often referred to as a ‘nutrient loading’ effect.  Trees can be pretty efficient at internal nutrient re-cycling, so this effect can persist for a few years after transplanting. 

So where does all this leave me on my homeowner recommendation?  For some elements, like potassium and phosphorus, we can base a recommendation on the standard soil test included in the program.  Unfortunately there is no simple indicator of soil N availability (see Scharenbroch and Lloyd (2004) for a thorough discussion).  Foliar samples would be the best bet but aren’t part of our testing program.  At this point, I’m leaning toward a simple visual assessment – Do the trees/shrubs look healthy and have acceptable color? (check yes/no).  If ‘yes’, don’t fertilize.  If ‘no’ add 1-2 lbs N/ 1000 sq ft.

Your thoughts?   

References

Day and Harris. 2007. Arboric. and Urban Forestry 33:113-121.

Ferrini and Baietto. 2006. Arboric. and Urban Forestry 32:93-99.

Harris et al. 2008. Urban Forestry and Urban Greening 7(3): 195-206.

Herms. 2002. Environ. Entomology 31:923-933.

Robbins. 2006. So. Nursery Assoc. Proc. 51:113-117.

Rose. 1999. HortTechnology 9(4):613-617.

Scharenbroch and Lloyd. 2004. J. of Arboric. 30:214-229.

Struve. 2002. J. of Arboric. 20:252-263.

Werner and Jull. 2009. Arboric. and Urban Forestry 35:252-262.

Mulch: Just Do It

A follow-up to Linda’s post about a recent study in Arboriculture and Urban Forestry that indicated mulch may not reduce evaporation of water from soil as we generally assume and which suggested that landscapers may want to re-evaluate their mulching practices.  As Linda noted, we have some real concerns about this conclusion and believe that proper mulching of landscape trees and shrubs has well-established benefits.

First, I don’t question the results present in AUF article.  As my grad students frequently hear me say, the data are the data.  But we need to bear in mind the paper is looking at one aspect of one of the impacts of mulching.  As Linda notes there are plenty of data to suggest that mulching does conserve soil moisture and she included some data from one of my studies which demonstrated this.  But there are other benefits to mulching beyond improving soil moisture.  I’d like to mention two here; one is a practical observation, the other is based on data from another study.

Preventing lawn mower blight and string trimmer trauma
From my observations and experience, one of the biggest and perhaps least appreciated benefits of mulch is keeping mowers and weed whips at bay.  I’m not aware of specific data, but damage by trimmers and mowers has to be near the top of the list of causes of mortality and long-term damage of new landscape trees.  A mulched zone around trees provides a buffer and simplifies maintenance operations. It’s an easy, simple and effective way to eliminate a major cause of tree distress.  A no-brainer.

Young, thin bark is no match for mowers and trimmers


Mulch protects trees and simplifies maintenance operations

Reduced soil temperatures
We conducted a trial a few years ago to look at the impacts of plastic mulches to improve establishment and early growth of Christmas trees. http://www.hrt.msu.edu/assets/PagePDFs/bert-cregg/cregg-et-al-2009.pdf  In a bit of serendipity we added a treatment at the last minute because our research station had some leftover wood chips from another project.  The trees mulched with wood chips were not irrigated but grew almost as much as trees in the plots that were irrigated.  What was especially impressive was the insulating effects of the wood chip mulch.  We installed probes to measure soil temperature 2” below the soil surface that we logged continuously.  During a July heat wave we found that soil temperatures were up to 10oC (18oF) cooler on the wood chip mulch plots than on the bare-ground plots.  Reducing soil heat load has profound implications for reducing root respiration and improving overall root function.

Soil temperatures were continuously logged on bare ground plots (foreground) and plots with wood chip mulch (background)


Soil temps peaked at around 38C (100 F) on bare ground without mulch (green dots);  max. soil temps were about 28C (82F) with wood chips (purple squares).

As Linda noted in her comprehensive review article, mulching has a myriad of benefits for landscape trees and shrubs.  It is important that we continue to look at all the various aspects of mulching and understand how to maximize the benefits (or reduce negative impacts) of mulching but in doing so it’s important to not lose site of the bigger picture.  While individual studies may yield conflicting data, on the whole, the preponderance of evidence and practical considerations come down strongly in favor of mulching