The Garden Professors™

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. 

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.

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.

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.