Diagnosing plant problems

As an Extension Specialist working with nursery and landscape issues, I’m frequently called upon to troubleshoot problems with trees and shrubs in various settings.  Sometimes it’s residential or commercial landscapes, sometimes nurseries, sometimes Christmas trees.  So naturally I was intrigued when the most recent issue of American Nurseryman featured a cover story on diagnosing nutrient deficiencies in plants.  The article was written by Dr. Gary Gao, Extension specialist with Ohio State University.  The article http://www.amerinursery.com/article-7428.aspx is good and does a good job on covering the basics.  However, the introduction of the article also hit on one of my pet peeves – and what is the Garden Professors for if not to vent on our pet peeves.

The intro states:

"If you have a good understanding of the function of plant essential mineral elements and a familiarity with common symptoms, common mineral nutrient disorders can be diagnosed quite easily."

Maybe I’m just trying to justify my own existence, but I find diagnosing nutrient disorders anything but easy.  This article and countless extension bulletins and factsheets imply that you can diagnose nutrient problems simply by matching leaves from your tree or shrub to a photograph showing the same symptoms.  To which I have three words: Ain’t gonna happen.  For the upper Midwest, I can think of exactly two landscape nutrition problems that I would be comfortable diagnosing by visual symptoms; iron chlorosis in pin oak and manganese deficiency in red maple.  Beyond those two I would want information from foliar samples and soil tests, as well as some site information before concluding the cause of a plant problem.

The main issue, of course, is that plant problems rarely come gift-wrapped.  Nutrient deficiencies (or, rarely, toxicities) are often confounded with other site issues; poor drainage, excessive drainage, too much sun, too much shade, insect damage, diseases, salt exposure.  As I’ve said many times, it’s much rarer to find a ‘smoking gun’ than not.  Usually it’s process of elimination with a best case scenario where you can compare symptom and foliar analyses of  ‘good’ and ‘bad’ plants.  But I think we do a disservice to landscape and nursery professionals and homeowners to imply that identifying the cause of a problem is as simple as picking the right suspect out of a line-up. 

Green candles identified

Not many guesses this week – too many Halloween parties?  In any case, Hap was correct – this is a closeup of the growing edge of Euphorbia lactea ‘Cristata.’  The "candles" on the edge are tiny leaves that appear whenever water is abundant but shed quickly during dry periods:

Thanks for playing, and Happy Halloween!

The Wrong Message

Every once in awhile I’ll see a new garden product that really speaks to me.  Something that promises spectacular results on some garden problem that I’ve had to deal with before and attacks it in a novel way.  Then I’ll read the advertising materials for the product and be let down before even trying it.  Such is the case for a new product called Liquid Ladybug (which, by the way, is one of the niftiest product names that I’ve ever seen — so there’s a win for the company!).

According to the manufacturer Liquid Ladybug is a spray-on product which kills spidermites, evaporates quickly from the plant, and which has organic plant oils as its main active ingredient.

So far so good — and even believable.  Plant oils can kill spider mites.  Of course simply wiping the plant with a cotton swab soaked in isopropyl alcohol can do that too — or you could easily make up a soapy spray to spray on the plant which can do the same thing.  Still, the claims don’t seem too bad so far.

Here’s the part that I have a problem with — you can, and are all but encouraged to, spray this stuff with no protection (like gloves).  See the website here .  Is this a bright thing to advertise?  Many plant oils don’t agree with eyes, mucous membranes, or beneficial insects, and let’s not even get started with allergies!  In my opinion this is reckless, foolish advertising.  Pesticides, organic or not, need to be respected.  Without that respect we inadvertantly put ourselves into bad situations. Another problem with this products is that it is likely to kill any predatory mites or other soft bodied beneficial insects just as readily as it kills bad mites.

And check out the price of this stuff!

My advice, skip this product and use insecticidal soap, or, if you’re anxious to try something new, try a beneficial insect such as the big eyed bug or minute pirate bug.

Today in Cucurbit News…

Cucumbers are one of the most widely-grown vegetables in the world.  Baker Creek Heirloom Seeds (a great place to buy unusual and international veggie seeds) lists 51 varieties from North America, Southeast Asia, China, India, Mexico, and Europe.  Dark green ones seem to be in the minority – yellow, white, orange and red skins in shapes round to elongated dominate.

Cukes traditionally have a few nutrients including some Vitamin A from carotenoids and beta carotene, but have never had the reputation as nutritional power house. Watery and gas-inducing, yes.

Researchers with the USDA have recently released a cucumber high in beta carotene.  No "frankencuke" this; all the crossing was done by traditionally breeding methods (including bees and self-pollination).  Lots and lots of crosses with a warty, round-ish chinese cuke (Cucumis sativus var. xishuangbannanesis) and some standard pickling cukes has resulted in a stable cultivar that has the smoother skin and proper proportions of marketable pickling cucumbers (there are lots of marketing standards associated with most fruits and veggies).  But the big news is the orange interior, specifically the endocarp (the jelly-like stuff around the seeds) and the mesocarp (the fleshy part that is the whole point). It’s orange because it’s full of beta carotene  (mesocarp is 2.7 micrograms per gram of fresh fruit compared to 0.02 micrograms per gram with a traditional white-fleshed variety.  Even more impressive is the jump in endocarp beta carotene – from 0.16 micrograms per gram to 7.5 micrograms per gram).  I don’t believe the USDA is going to release this particular line directly to the public, rather they’re offering the genetics (two recessive genes control the beta carotene content) to other breeders.  This means other breeders can use it in their own breeding program to bring more nutritional value to their specific lines, at which point varieties will become available to growers/gardeners. Orange tzatziki!!!

from Staub, J.E., P.W. Simon, and H.E. Cuevas.  2011. USDA, ARS EOM 402-10 High β-Carotene Cucumber. HortScience 46:1426-1427.

(Linked, but my guess it won’t work if you don’t have a HortScience subscription or institutional access, sorry) 

A little about bugs

I’m not much of an entomologist.  (Okay, I’ve never had a single bug-related class.)  But I do appreciate insects in all of their bewildering shapes and behaviors.  And after this weekend I’ve become a little more entomologically educated.

I spent the weekend in Prescott, Arizona at the annual MG conference.  Besides meeting lots of great Master Gardeners (and Extension educators) in that state, I also met Dr. Whitney Cranshaw from Colorado State University.  He gave a keynote talk called “Gardening for Insects – or not!”  This was a seminar that presented positive and negative aspects of gardening for butterflies, honeybees, and other favorite insects.

Here are just a few of the nifty things Whitney had us consider:

  • Not all butterflies are nectar feeders; some prefer rotting fruit or dung.  Hmmm.  I might have to limit my varieties.
  • The caterpillars of some striking butterflies might need you to share some garden greens.  Larvae of black swallowtail butterflies eat parsley, fennel, and dill, for example.  Accepting damage on these plants will ensure a healthy population of adults for your viewing pleasure.
  • It’s best to accept some degree of pest insect presence, like aphids, to provide food for beneficial insects.  Insecticides are not part of a successful garden for insects.
  • The first bumblebees of the season are always small; they’re produced by overwintering queens whose resources are limited.  These new workers help gather more food, so that those produced later are larger.

Whitney has a fantastic collection of photos of insects, up close and personal.  Some of these are also in his book Garden Insects of North America (Princeton Press). It’s over 600 pages of full-color photos and engaging text.  Instead of being organized by family, it’s organized by feeding habit, so you can quickly look up and identify whatever weird bug you’ve found snacking on your snapdragons. There are sections on how to manage pest insects, and a chapter dedicated to beneficial bugs. 


Amazingly, this book is only $29.95.  I bought one.   

Finally, I have to recognize Dr. Cranshaw as one of an unusual breed of faculty.  He is passionate about educating adult audiences like Master Gardeners, and indeed his book is dedicated to entomology educators and the nationwide Extension system.  What a great resource for gardeners everywhere!

The people have spoken…

OK, the results are in for our reader poll to design a landscape tree transplant study here at MSU next spring.  And the winner is…er, I mean, winners are: Root ball manipulation and Fertilization at the time of planting.  Root ball manipulation drew 74.3% of the responses, Fertilization was chosen by 63% (voters could chose more than one favorite topic).  All other proposed topics were under 40% (Mycorrhizae – 37%, Crown reduction- 31%, Cambistat – 11.4%, Bioplex – 11.4%).  I will put pencil to paper and survey the trees and space available for a trial.  My initial thought is that we can do a 3 x 2 factorial experiment with 3 types of root-ball manipulation and 2 levels of fertilization.  Root-ball manipulations will include two popular recommendations: 1 – ‘shaving’ the root-ball to remove circling roots; 2 – ‘teasing’ the root-ball to untangle circling roots; and 3 control e.g., planting the root-ball as is.  The two fertilizer treatments will be 1 – 400 grams Osmocote and 2 – control, no fertilization.  The goal is for this to a long-term study – hopefully at least 5-years.  The principal response variables will be survival and growth.  If time and resources allow we will collect water relations data such as water potential and stomatal conductance during the transplant year. 

I was a little surprised that Cambistat did not rate higher.  This product has been heavily marketed to arborists and has been touted to reduced transplant stress.  The active ingredient, paclobutrazol, is a well-known plant growth retardant.  The theory is that it reduces stress by limiting crown expansion and reducing stomatal conductance while roots continue to develop.  I’ve actually been a bit intrigued and may set up a little side study to satisfy my own curiosity.

Thanks to all who took the time to vote.  I look forward to keeping you all posted on the trials! 

Any PR is good PR…I think…

Virginia Tech (my institution of employment) does a good job of bringing newsworthy research and outreach stories to the university’s home page.  With a huge college of engineering, robotics seems to be the dominant theme (no matter how lame the robot is) closely followed by solar-powered cars etc.  So it’s a rare and thrilling event when a news items with a horticultural topic is featured on the VT web site!

As I read it yesterday, my heart sank a bit. A little less drama and a little more fact-checking would have gone a long way (the demise of which is a re-occurring gripe here on Garden Professors). I do seriously appreciate that something horticultural made the news,
and the efforts of the writers to make it interesting. I also realize a
great majority of the readers will not split hairs like I have.

If you’d like to read the brief and pleasant article, click on the link. My carping will make much more sense.


In a nutshell, a lab associated with Virginia Tech has developed a tissue culture protocol for the propagation of an Icelandic poppy cultivar at the behest of a cut flower grower.

Hurrah, right? Absolutely. But the article mucks it up a bit.

(On with the hairsplitting!!!)

1) Icelandic poppy (Papaver nudicale) is in no way endangered or about to go extinct. You can buy seed by the pound. The cut flower grower mentioned  (a fabulous grower and just as wonderful a person) has a favorite cultivar. ‘Temptress’  is a selected, named variety of P. nudicale – of which there are many (20? 30?).  Cultivars are lost all the time, but they do not "become endangered" or  "go extinct" – this terminology implies it is found in the wild. Which ‘Temptress’ is not, because it is a man-made selection.  If ‘Temptress’ is indeed a hybrid, the parents could possibly be crossed to hopefully the same end. Extinct…is forever. 

It may be rare, it may be difficult to propagate by the usual means of seed or cuttings, and micropropagation has apparently worked to sustain the variety. Micropropagation has been used to save many heirloom fruits and vegetables.  But back to our poppy.  True, it may not continue to exist if a viable method of propagation is not found, as the grower notes.  But the authors incorrectly interpreting the quote.  The world is not losing a species; rather, one cut flower grower is losing his favorite color of poppy.

2) Though fine scientists in their own right, the two faculty named in the article did not (nor did they claim to) "pioneer a technique known as micropropagation."

I think I just heard Dr. Toshio Murashige have a cow.

Micropropagation (a form of tissue culture) has been around since the 30’s and is now a HUGE industry around the world.  For example, nearly every orchid and fern sold at Home Depot is a product of micropropagation.  

Micropropagation involves many variations on and combinations of plant hormones, growth regulators, minerals, etc.  The researches mentioned (and their staff) formulated a successful protocol (recipe) for this particular species. It was indeed a challenge, and it’s great that they came up with the correct combination of the umpteen variables required to generate root and shoot growth. This is often called "cracking the code" and would have been the correct angle for the article authors to take.  Finally, microprop is NOT a “plant breeding method” as stated in the photo caption. And since the Icelandic poppy is not fragrant, there will be no "fragrant scent wafting." No. Wafting.

Though it sounds lovely.  Thanks for listening.

The Genetically Modified Kentucky Bluegrass Problem (The Anger As Promised)

One of the nice things about my job is that I get to work with a lot of other researchers who work in a lot of different areas.  One of these areas is molecular biology and I certainly know people who have genetically engineered plants to do one thing or another.  Maybe it’s because I know so many people who work with them, but I’m not fundamentally opposed to genetically  engineered crops. Which isn’t to say I’m not concerned about certain genetically modified crops, but in general I think that the systems we have in place to review them have done a decent job of making sure that nothing too terrible is released.

Until now.

A few years ago a grass called creeping bentgrass was genetically modified to be resistant to Roundup.  This grass was never released to consumers, but it was released for testing, it escaped, and now this grass, though not widely distributed, has made a pest of itself in various spots – and we can’t use Roundup to control it. 

The above is obviously a problem, but not the problem I’m concerned about.

This past July APHIS (Animal and Plant Health Inspection Service — a department of the USDA) confirmed that a new genetically engineered Roundup resistant Kentucky bluegrass was not subject to regulation because it had been made without using organisms that are considered pests (Most genetically modified plants are).  So, for the first time, the government is actually saying that a genetically modified crop is exempt from oversight.  The other two governmental entities that usually look at genetically modified organisms, the EPA if a plant produces a pesticide and the FDA if a food is being produced, don’t need to look at this grass because it doesn’t produce a pesticide and it isn’t a food.

This, in my opinion, is insane.

This non-native grass is a known invasive across the Midwest where it fares pretty well out on the plains.  In fact, according to the USDA (which includes APHIS) it is listed as an invasive weed in the Great Plains States and Wisconsin.  The USDA also lists one of the preferred controls for this grass as glyphosate (Roundup).


Look, I know this is kind of a tricky thing what with the way that this grass was made and all.  But it seems to me that if APHIS wanted to consider this a potentially noxious weed it could, thereby mandating some review. 

What it comes down to is that I am very scared that the company which made this grass – Scotts Miracle-Gro — might actually release it and cause some problems similar to those caused by the Roundup resistant creeping bentgrass – but at a much larger scale.  Sure, there are other pesticides which can be used on Kentucky bluegrass if it gets out of hand, but losing one that is so effective and so safe (on a relative scale of course) seems crazy.  I guess you could argue that using this grass might reduce the use of other, scarier, chemicals in yards, but jeepers crimeny, wouldn’t you like some non-partisan governmental organization to at least look at it?

In my opinion this whole thing is just nuts.  And let’s not lose sight of something that is potentially even scarier: By figuring out how to avoid government regulation, Scotts Miracle-Gro has drawn a map for other companies to avoid regulation with their genetically modified crops.

Reader input wanted for new book

(Note:  I’ll be doing another blog posting later today.  Just want to be sure I get this out.)

I’m writing a new book on plant physiology for gardeners – a book that explains how plants work and why they sometimes do weird and unexpected things. I’d like to hear what kind of “how” or “why” questions you’d like to see answered in this type of book.  Please add your comments to this post, or send them to me directly. And if there are other gardeners you know who might want to send suggestions, be sure to send them the link!