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!