Friday Can O’ Worms

I was pleased to see that at least two of you dug into the literature over the weekend to read these papers!  (I can still remember the first time as a Master’s student when I was assigned a journal paper to review.  I had NO idea what, exactly, I was supposed to be doing.  It took a long time to figure it out.)

In any case, kudos to Jimbo and Diana for their thoughtful comments – and for zooming in on the problems.  Indeed, Jeff and I conclude there is likely a fertilizer effect on the plants – and a healthy plant is better able to resist insects.  Secondly, the speculation at the end of the paper regarding root uptake of phenolics from the vermicompost – compounds that weren’t even measured, much less monitored for uptake – is totally unsubstantiated and in fact is not feasible, given root physiology.  I’ve pasted my draft to the journal editors below, which explains this a bit more.  (Jeff also has some choice things to say, and I’ve added his comments as well.)

From LCS:  “I recently read the article by Edwards et al. entitled “Suppression of green peach aphid (Myzus persicae) (Sulz.), citrus mealybug (Planococcus citri) (Risso), and two spotted spider mite (Tetranychus urticae) (Koch.) attacks on tomatoes and cucumbers by aqueous extracts from vermicomposts” (29(1): 80-93).

“The article presents evidence that the use of vermicompost teas increased the resistance to damage from these pests.  As the authors state “there are many reports in the literature of organic nutrient sources decreasing numbers of pest arthropods.”  This seems a logical conclusion given that the authors have provided an additional nutrient source to their treated plants (vermicompost extract) that was not available to the control plants (which were drenched with water).  The treated plants were better able to manufacture anti-herbivore compounds as a result.

“Yet the authors then venture into unsupported speculation that this resistance was due to the uptake and transport of water-soluble phenols by the roots and into the leaves of these plants.  In the authors’ words:  “these diverse results all point to the probability that water-soluble phenols, extracted from the vermicompost during aquatic extraction, taken up into plants from soil receiving drenches of vermicompost aqueous extracts, could be the most likely mechanisms by which vermicompost aqueous extracts can suppress pest attacks.”

“Not only are there no data or other direct evidence to support this speculation, but the likelihood of such uptake is highly unlikely if not impossible.  The water/nutrient uptake mechanism in plant roots is cellularly regulated, particularly at the endodermis, where all solutes must pass through cell membranes prior to entering the vascular tissue.  No such transport has ever been documented in the literature, though the authors report “There have also been suggestions of these effects being due to the uptake into plants of phenols from organic manures (Ravi et al., 2006).”  This latter paper, however, measures the presence of phenols and their associated enzymes in the plant tissues, not the uptake of soluble phenolics.  Plant physiologists and biochemists have long known that plants are capable of synthesizing a wide variety of phenolic compounds used to ameliorate abiotic and biotic environmental stresses.  I am surprised that the authors did not discuss their theory with plant scientists at their institutions.

“It is disappointing that the authors were not discouraged during the peer-review process from making unsubstantiated, fantastic claims about the mechanisms underlying their research results. ”

From Jeff:  “Though we do not discount the possibility that compounds may have been present in the vermicompost that could have been taken up by the plant’s roots, we think it much more likely that there was a fertilization effect which caused the plants to grow more rapidly and/or which allowed the plant to defend itself more effectively using its own defensive mechanisms. The authors of this paper discount this effect by stating that “It could not be caused by uptake of soluble nutrients since all of the experimental treatments were supplied regularly with all the nutrients that they needed from Peter’s Nutrient Solution, which was applied to the experimental plants three times a week.” but do not include any evidence to back this statement up. This is a fatal flaw. In fact, the authors don’t even provide any data regarding the concentration of nutrients that were added. Simply stating the analysis of the Peter’s fertilizer which was used provides us little data as they could have mixed this up at any concentration before applying. Was nitrogen applied at 10ppm? 600ppm? Likewise, though the authors tell us the concentration of nutrients in the vermicompost used, no indication of the amount of nutrition in the compost extracts is given. If these analyses of nutrient content turned out to be too expensive the authors could simply have grown additional plants without exposing them to the insect pests. By then comparing plants which had been grown with extracts to those grown without the effects of the extracts on growth would have been made obvious. Another significant problem with this paper was the lack of information regarding the variety of tomato which was grown. Tomatoes have various resistance mechanisms to defend themselves from insect pests including, but not limited to, both glandular and non-glandular trichomes. Many papers over the years have shown that the density and chemical composition of these trichomes is affected by both the plants parentage and by nutrient concentration.

“In short, it is difficult to believe that even a novice researcher would provide the paucity of information and experimental data that these researchers did which might elucidate the presence or absence of a fertilization effect. The fact that the first author of this study is a seasoned researcher gives the impression that the objectivity of this research has been compromised. This impression is only strengthened when we discover, at the end of the paper, that this research was funded as a subcontract to a grant for small businesses, in this case the Oregon Soil Corporation. It seems logical to assume that this paper was published as a gimmick to promote the business interests of a producer of vermicompost rather than for any furthering of science. You have done your journal a great disservice by publishing it.”

Friday puzzler revealed!

Lots of discussion about the mysterious white streaking on the hedge.  The pictures below show a little more detail than those on Friday:

As you can see, Jimbo was on the right track when he suggested the hedge might be near a parking lot.  But it’s the heat escaping from the engine compartments that’s been causing the damage. 

(I am now committed to find some good photos of urine damage by dogs, donkeys, or drunken frat boys!)

Friday puzzler addendum

OK, I know we gave you a tough assignment for the weekend, so I want to post something fun as well.  (Think of this as dessert after your healthy meal!)  Take a look at the photos below:

This hedge is regularly sheared and no one part of it has been maintained any differently than another part.  Both sections of the hedge face east, and the damage is anywhere from 2 to 4 feet from the ground.  What do you think has caused the damage?

Explanatory photos reveal all on Monday!

Friday puzzler: Opening a can of worms

Part of being a Garden Professor is evaluating, interpreting, and passing on good science to the rest of the gardening world.  I was recently made aware of two articles soon to be published in Crop Protection and Pedobiologia, both peer-reviewed, scientific journals.  (You can download these articles just by clicking on the highlighted journal names.)

Briefly, what one expects from a scientific article is (1) a statement of the research question (the hypothesis) to be investigated, (2) a clear description of the materials used and procedures followed, (3) a listing of the results, along with their statistical significance, and (4) a discussion of the results, including whether they supported the hypothesis.

    

Both articles focus on the use of vermicompost teas as a way of reducing pest damage on greenhouse grown crops.  If you’re not familiar with this product, it’s made using worm castings and water in an aerated system. The researchers conducted one large experiment and divided the results into two parts for publication. Therefore, the materials and procedures were the same for both articles, and you’ll also see that the conclusions are likewise the same.  (My point – you really only need to read one of these articles.)

 

I sent these articles and my evaluations to my GP colleagues; at least two of us will be sending letters to the editors of both journals expressing our concerns.  Jeff thought these articles provided a great opportunity for our blog readers to look over our shoulders and see what we do.  We don’t question the results that the investigators got, nor do we have any argument with the statistical analysis.  We do question the authors’ interpretation of the results.

So here is your assignment for the weekend:

(1)  Read the methods section carefully to understand the differences between the treatments (the vermicompost tea addition) and the control. Can you think of an alternative reason for the results the researchers found?
2)  What additional flaw do you see in the discussion section in terms of the proposed mechanism of protection conferred by the vermicompost tea treatment?

On Monday, I’ll post the draft of the letter that we’ve drafted to the journals.

Oh, and if you have any questions, please post them!  We will answer them the best we can.

Autumn color puzzler

Here’s a photo I took in Buffalo about 20 years ago.  Buffalo, like many places in the northeast part of the country, has fantastic color changes in the fall.  This maple seems to have changed its mind part of the way through the process:

What do you think caused part of this tree to retain its green leaves?  Answer and another photo on Monday!

Mysterious tree failure…

Here is this week’s plant puzzler.  This mature tree just fell over one summer day.  There had not been any significant wind, the soil was well-irrigated (but not overly wet), there had been no construction work or other root-zone disruption.  There were no significant pest or disease problems.  I’ve posted two photos from different angles, and will show one more photo on Monday.  Why do you think the tree failed?

Epicormic mystery solved!

Good morning (at least it is in my time zone)!   And welcome to those of you who found us through Blotanical or another blog site.  We love seeing the increased participation on our blog.

Since I am a teacher at heart, I was glad to see so much thoughtful discussion over the weekend.  Many of you suggested that pruning for vehicular traffic was the trigger for this growth, and it’s true that removing large limbs or heading back branches will result in vigorous epicormic growth.  But I cheated on the photo and cropped it above the point of interest.  Here’s the entire photo of this tree:

You can doubtlessly see that dark line encircling the trunk just above the two branches with the shoots.  Here it is close up:

Venturing around to the back of the tree, we can see the source of this line – neglected staking wire that has now been enveloped by the trunk.

What this wire has done is to girdle the phloem elements, which as you’ll remember from basic plant science, are directly below the bark and the cork cambium.  Without functional phloem, nutrients from the crown can’t reach the roots.  Since the two lower branches were spared this girdling, they can still transport sugar to the roots, so the tree hasn’t died.  But now it’s directing resources (water and nutrients) into the lower branches, where the new epicormic shoots are forming a new, functional (albeit ugly) crown.  In time, the original crown will probably fail; there’s already evidence that the trunk is dying:

What could be done with this tree?  If the wire were removed or at least cut so that the trunk could pop it apart, there is the possibility that the crown could have been saved.  But since the upper trunk already looks severely compromised, it’s probably too late.

As a sad update to this set of photos, the owners had a tree “service” (I use the term loosely) to remove all the epicormic shoots from the lower limbs!  I will let you know when and if the whole thing fails.

Oh, and gold stars to all who participated in the quiz!

Quiz time!

One of the things we Garden Professors can do is give tests!  And the nice thing is you don’t get penalized for being wrong.  So this will be my inaugural Plant Puzzler.

Below is a photo of a tree with epicormic shoots on its two lower branches.  Epicormic shoots are vigorous, upright branches that have more of a juvenile than mature appearance.  They often appear when a plant has been stressed, perhaps by overpruning, or maybe the roots were damaged by construction:

So here is your test question.  Why are these epicormic shoots primarily (if not exclusively) on the two lower branches, and not elsewhere in the crown?  (You can’t see the top of the tree, but I promise there are no epicormic shoots up there.)  And what evidence would confirm your diagnosis?  While there is only one correct answer for this particular tree, let’s see how many possibilities you can come up with.

Answers and more pictures next week!