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Let It Snow!

Here in Minnesota one of the things that we need to worry about is the cold.  Over the winter we can see temperatures down into the -30s (even the -40s in the Northern part of the state) and it can damage many of the plants that we grow.  The tops of the trees are usually able to handle these types of temperatures — though a good heavy snowfall can cause a limb to collapse now and again.

The bigger problem is with roots which aren’t able to handle the cold like the top of a plant can.  Once you get 10 degrees or so below freezing you’ve killed the roots of most plants.  Fortunately the ground is a great insulator and doesn’t get nearly as cold as you’d think.  Once you get two or three inches under the surface of the soil temperatures will hover right around freezing for most of the winter.  The plants that are most susceptible to cold are those that are in containers because their roots are above the soil’s surface.  Nursery growers usually protect containers from the cold by consolidating them (pushing them together as in the picture below).

These containers are then covered with a layer of polyethylene fabric, about 6 inches of straw, and then another layer of polyethylene fabric.  Temperatures under the fabric rarely go below 26 degrees or so — even when outside temperatures stay around -20.  Most plants come out fine — our biggest problem is that sometimes voles and mice will take up residence under the tarp and eat the plants — which isn’t a big deal unless its a research project — in those cases we will often use poisons or, more frequently, repellents.

The only thing better than this method is snow.  If we could count on snow every year we wouldn’t bother covering the plants at all.  Snow is the best insulator that we have.  Under snow temperatures rarely go below 29 degrees or so.  So, despite the traffic problems that snow causes, nurserymen and landscapers are always happy to see snow on the ground before the really low temperatures hit.

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.”

Soap and Deer

Short post today — Linda appears to have transmitted her illness electronically over a couple of thousand miles — Thanks Linda!

I was reminded yesterday that it’s almost time for gardeners to start worrying about winter deer damage. With that in mind I thought I’d share with you my favorite research article on the subject.  It’s a little paper by Michael Fargione and Michael Richmond and published about 18 years ago.  You can find it here.

This paper attempts to establish how repellent bars of soap are to deer and comes up with some very interesting conclusions.  The first thing you should know is that no one type of soap appears to be better than another.  The second thing you should know is that soap does appear to stop deer from feeding around the soap — but the best you can hope for is a radius of protection of about a meter from the bar of soap itself — Can you imagine what that would look like if you were trying to protect the lower limbs of a large tree?  And finally, bar soap appears to attract voles.  Based on my reading, and my limited experience, I’ve found that almost everything that people say repels deer does repel deer — human hair, peeing around a tree, predator urine, dried blood — the issue is how long these repellents stay effective and how effective they are when the deer get really hungry.  The most effective commercial deer repellents tend to have “putrescent egg solids” in then (rotten eggs) — I once had a graduate student who needed to protect some hazelnuts from deer and she found that a mixture of a few eggs (2-4) mixed in a quart of water and sprayed onto the trees worked pretty well — and no, the eggs weren’t rotten.  This mixture should be sprayed about once every two weeks if possible.