Category: Cool Research

Bounce – it’s not just a fabric softening sheet…

…it’s an Integrated Pest Management tool!

[Note added after-the-fact: this was a  tongue-in-cheek bit of  hyperbole – kind of like “it’s not just a Job, it’s an Adventure.” Did not mean to imply that it actually IS an IPM tool. Very badly worded. Hence the beating I took in the comments. Live and learn.]

Fungus gnats (Bradysia spp.) are a pain in the bottom for commercial greenhouse growers. The adults are more of a nuisance than anything else –it just looks bad when a customer picks up your 6” pot of pansies and a bunch of little black gnats take flight.  It’s the larvae that are problematic. Adult females lay the eggs in especially damp growing media, and the newly-hatched larvae feed on the roots. There’s both direct damage and also speculation of easier infection of root-borne pathogens, of which there are plenty. 

 
Fungus gnat larvae, just making a living…

Standard control measures include insecticide drenches, biological controls including a specific strain of Bt (Bacillus thuringiensis – sold as GnatrolTM), nematodes, etc.  One of the easiest control measures is the one I teach my students: to not over-water, i.e. “grow dry”. But that can be difficult in a big greenhouse range with many different-sized containers, all which drain/dry out at different rates. Propagation houses also have high humidity levels and have to stay moist for rooting/germination purposes and are thus favored by fungus gnats.

Entomologist Dr. Raymond Cloyd of Kansas State University and his group were intrigued by Master Gardener anecdotes of dryer sheets repelling mosquitoes, though no research had been done. Could your common Bounce sheet also repel other pests? And, to take it a step further, what, exactly, repels them?  The answers are “yes” and “lots of volatile compounds.”

Their study was published last month in the journal HortScience. Honestly, I’ve never seen descriptors like “controls static cling” and “gives clothes a fresh scent” in a Horticulture journal. Hee! Plus the researchers made it clear this experiment specifically used Bounce Original Outdoor FreshTM. Still kind of humorous, but really good science and the part that’s usually overlooked in the translation to a News Story. Do NOT extrapolate results to include Bounce Spring Fresh, Fresh Linen, and certainly not Downy or Snuggle brands. 

The study had a simple design, releasing lab gnats (ha!) into a  many-chambered container and observing to which chamber the gnats gravitated to (or away from).  There were five different variations on this theme, including an alluringly soggy media sample; when the sample of fabric softener sheet was introduced, they stayed away in droves. All five experiments showed a fairly drastic aversion to the sheet. To determine what was fending off the gnats, they did a steam extraction on sheet samples and ran the condensate through a gas chromatograph – mass spectrometer to measure the volatiles.



Figure from Bounce® Fabric Softener Dryer Sheets Repel Fungus Gnat, Bradysia sp. nr. coprophila (Diptera: Sciaridae), Adults. Raymond A. Cloyd, Karen A. Marley, Richard A. Larson, and Bari Arieli, HortScience Dec 1 2010: 1830–1833

Well, there you have it. Linalool is a monoterpene alcohol found in lavender, basil, and coriander, and is known to be toxic to mites and insects.  Citronello is another monoterpene and lends lemony-freshness to lemon balm, pennyroyal, and rose geranium and has short-term “repellent activity against mosquitoes.”  Benzyl acetate, though not specifically mentioned in the results, is another natural fragrance compound, found in jasmine – and is also an industrial-strength solvent. One man’s solvent is another man’s perfume. Or fabric softener. I bet their lab smelled GREAT, by the way.

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Potted plants…really potted

A week or so ago my new friend Doug wondered about some gardening advice on the radio: would adding vodka to paperwhite narcissus make the flowers less “floppy?” The explanation he’d heard was that alcohol would burn the roots and reduce stem growth. Then today I received an email newsletter with the same intriguing information. This newsletter referred to a 2006 article that appeared in HortTechnology as the source of this information.

The study by Miller and Finan has generated a lot of interest in the gardening community, especially this time of year as people get ready to force bulbs for indoor blooms. Unfortunately, that enthusiasm isn’t evident among researchers. Neither the original authors nor any other researchers have continued this work; the HortTechnology paper has never been cited in any subsequent publication.

This is unfortunate – because inquiring minds want to know WHY alcohol causes narcissus stems to be shorter. Miller and Finan hypothesize that it’s simply an osmotic effect and allude to preliminary data that support this, “but additional work will be needed for confirmation.”

So I’ve looked into other scientific articles about ethanol and roots for insights into this phenomenon. There’s nothing on narcissus, but others have studied trees, forsythia, tomato and barley reactions to root-zone ethanol. In all of these cases, exposure to ethanol resulted in reduced root growth, decreased water uptake, and reduced leaf transpiration.

How does this translate to shorter stems and leaves? A reduction in water uptake and movement through the plant – that is, from roots through the stems and out of the leaves – can reduce movement of growth regulators like cytokinins from roots to stems and leaves. It can also mean that the plant contains less water and is less turgid as a result. Both growth regulators and cell turgidity are important in cell division and elongation. Reduced cell expansion will cause stems and leaves to be shorter and/or smaller as a result. This same phenomenon can be seen in plants grown under saline or droughty conditions: these plants are always smaller than their normal counterparts.

So what your grandmother used to warn you about is true – alcohol WILL stunt your growth!

Ignorance and the so-called “bogus” bee study

I’m angry.  Really, really angry.  And it’s all Kenny’s fault.

Kenny S., one of our long-time blog followers, alerted me to a blog posting dismissing a new study on colony collapse disorder (CCD). The post was devoid of any evidence of bogusness, other than a link to “great reporting” by New York Magazine. Aside from the general snarkiness of this article, we’re breathlessly informed that Fortune magazine (a hotbed of scientific inquiry) uncovered an unholy connection between the lead author (Dr. Bromenshenk) and Bayer.  That article recounts Dr. Bromenshenk’s sins, which include (1) accepting research money from Bayer, (2) not serving as an expert witness in a legal case against Bayer and (3) not studying every single possible cause of CCD.

Next I looked at the contested study, which is in an online journal.  Apparently none of the reporters/bloggers have bothered reading this, because they could easily discover the following:

1) there are 18 authors from many institutions, not just Dr. Bromenshenk and “Army scientists”;

2) the methodology was specific for protein analysis (not for pesticides nor any other nonliving factor);

3) funding was not provided by Bayer or any other corporation;

4) competing interests, such as Dr. Bromenshenk’s company, are openly acknowledged;

5) the article does not suggest anywhere that pesticides are blameless in CCD.

The body of the article is pretty technical and I’m not an entomologist. Still, this is in a peer-reviewed journal (albeit online rather than print).  You can see the review process and the list of academic reviewers if you were so inclined (as anyone who writes about science should be). Thus, qualified scientists (in addition to the 18 authors) find this to be a legitimate study.

Let’s look at Dr. Bromenshenk’s research history.  (For the record, I don’t know him and had never heard of him until yesterday.)  He’s published at least 26 scientific articles (in journals including Science) on various aspects of bee biology for the last 27 years.  To do these studies, he needs funding.  Guess what?  Universities don’t provide funding.  Magazines don’t provide funding.  Bloggers don’t provide funding.  Other than a handful of relevant government agencies (like NSF or USDA), most big grants come from corporations.  Like Bayer.

Now this is why I’m mad. There’s widespread perception among nonacademic types that corporate grant money “buys” results. That’s insulting. Most scientists do what they do because they love the thrill of discovery. There’s no thrill if you’ve rigged the results. Moreover, if you rig the results you’re going to be found out…eventually. A scientist with 27 years of credible, scientifically reviewed research is hardly a data rigger. And he’d have to convince 17 coauthors to go along with the scam.

Near the end of the Fortune article (and ignored by subsequent articles and blogging) was Dr. Bromenshenk’s efforts to get Bayer and the beekeepers to talk to each other. Though he was able to get Bayer to appoint a beekeeper advisory board (to assist with experimental design) in an effort to increase “trust and transparency” with the public, it hasn’t been terribly successful.

So here we have a man who’s devoted more than a quarter of a century to studying bees, who has published extensively in the peer-reviewed literature, who is trying to shed light on why bee colonies are dying, and who has tried to bring the pesticide industry and environmentalists to the same table.  You tell me why he’s being pilloried.

Why I like science (our visiting professor returns)

I like science.  I see it as a way to figure things out.  It creates a combination of a) things we’re pretty sure of (facts about the shape of DNA, the optimum pH for certain plant species, and theories consistent with such facts, for example) and importantly, b) questions we can ask next.  When research is designed to answer those new questions, the results will either support the things we’re pretty sure of and lead to an expanded understanding and new questions, or they won’t support what we thought we knew and the results will lead to a different understanding and new questions. 

Scientists do research, but it’s only useful if others find out about it.  Imagine what more Darwin might have come up with had he known about Mendel’s work on inheritance of traits.  And when a researcher shares his or her research results at a meeting or in a publication (like many colleagues got to do in Portugal last week, lucky dogs), they are opening their research up to critique from others.  Thoughtful critique is exciting.  It may feel like an attack on the researcher, but it is usually an attack on the borders of what is known. 

Stay with me, this relates to professors AND gardens.

One of my favorite papers full of criticism is about ‘Talking Trees’.  This idea emerged in the early 1980’s (and given a catchy name) when research was suggesting that trees with damaged (manually torn) leaves could cause chemical responses in nearby plants.  It was concluded that maybe, just maybe, one tree was acting as a beacon, sending out signals when damaged by a herbivore.  Then a tree fortunate enough to receive the signal could begin to mount a defense against herbivores before being damaged itself.  A paper published in 1983 (Baldwin and Schultz, Science, 221:277–279) showed evidence for this kind of communication.  But then an article published in 1985 [Fowler and Lawton, American Naturalist, 126(2):181–195] called into doubt the conclusions of the 1983 paper.  As the authors of the 1985 paper lay out, the statistical design and analysis of the 1983 paper was flawed.  We shouldn’t trust the conclusions without more research.  And one thing I really like about the new research detailed in the 1985 Fowler and Lawton paper, they clearly lay out potential shortcomings of their own work, and even consulted about these pitfalls with an author of the 1983 paper (which they thoroughly criticized!).  This is where the “what questions to ask next” are generated, and the authors did some of the heaviest lifting for us there.  Such discussion and disclosure helps to expand knowledge in the field, but I like it in this particular instance because it also gives a sort of narrative about thoughtful criticism in science.

So this does relate to gardening, because there is a lot more going on out there than just ‘growing’.  There has been a lot of research since 1983 on inter-plant signals, and it does seem to happen in the lab, but also at close distances in nature with some plants (the sagebrush-tobacco relationship is best-studied).  The research has also shown this signaling can reduce herbivore damage on undamaged plants.  For brief reviews, see Dicke et al. [Trends in Plant Science, 2003, 8(9):403-405] or Baldwin et al. (Science, 2006, 311:812–815).  And as an added bonus, the chemicals released by herbivore-damaged plants can attract carnivores that EAT herbivores (predatory mites and parasitoid wasps, for instance).  Some of the chemicals that may be involved in these responses?  Methyl jasmonate (smells like jasmine) and methyl salicylate (wintergreen oil).  Your garden is doing a whole lot more than you realize just under your nose, and I haven’t even MENTIONED all the plant and invertebrate sex, or the kinky inter-kingdom pseudocopulation that might be going on out there.  Plants and science are awesome. 

Need a lift?

One of the topic groupings for our posts is titled ‘Cool research’.  The subject of today’s post has actually been around for a few years but I still think it’s pretty cool.

 

When we think of interactions between plants we usual think of negative interactions such as competition for water and nutrients or maybe allelopathy.  But there are cases where plants can benefit each other.  One of these is a phenomenon known as hydraulic lift.    Hydraulic lift is the passive movement of water from roots into soil layers with lower water potential, while other parts of the root system in moister soil layers, usually at depth, are absorbing water.  In essence, plants will large, deep root systems (usually trees) bring soil water from depth to the surface where it can be used by other plants.  Hydraulic lift has largely been observed in arid and semi-arid ecosystems, though it can occur in wetter systems as well.  For me, the research that went into discovering hydraulic lift is as fascinating as the process itself.

 

One of the key lines of evidence for hydraulic lift comes from studies of stable isotopes.  As you may recall from college or high school chemistry, atoms of each chemical element have a certain number of protons and neutrons, which give it its mass.  A small portion of each element has extra neutrons resulting in a ‘heavy isotope’.  In the case of hydrogen, approximately 1 in 6400 atoms is heavy hydrogen or deuterium (2H).  Interestingly, the amount of 2H in water can vary depending on the source of the water; this ratio is termed an isotopic signature.  By comparing the isotopic signature of ground water and rain water in a given location, researchers can actually tell where certain plants are getting their water.  One of the classic studies in this area was conducted by Todd Dawson at Cornell in the early 1990’s.   Dawson analyzed isotopic signatures of groundwater, rainwater, and water in various plants around sugar maple trees and determined that many herbaceous plants contained a high proportion (up to 60%) of groundwater.  But how do shallow-rooted plants obtain groundwater?  The neighboring maple trees bring it to the surface from ground water as they are hydrating overnight.  An efflux of water from the maple roots results in a localized increase in soil, which can be utilized by other plants: hydraulic lift.

 

How important in hydraulic lift in most landscapes?  Probably not very.  Demonstrating significant hydraulic lift requires the proper hydrology (shallow ground water accessible to trees or shrubs but not smaller plants) and limited rainfall.  But the importance goes deeper (no pun intended!).  Prior to the advent of stable isotope techniques, many would have been dismissive of the concept of hydraulic lift.    Since 1993 over 100 papers have now been published on the subject.  To me, the ultimate value of Dawson’s work and related studies is showing the importance of keeping an open mind and being receptive to new ideas. 

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Restoration ecologists – you need us!

Restoration ecology – the science of restoring degraded ecosystems – is another branch of applied plant sciences.  Oddly enough, very little plant science makes it into the scientific literature of this field.  This has driven me nuts for a number of years after reading an endless stream of papers where no mention is made of how plants are selected, installed, and managed.  Or worse, some ancient horticultural practices are used – like amending the backfill with organic material rather than using just the native soil.  Here’s what that will lead to:


Native soil discarded in favor of “lite-n-fluffy” amendment

The whole story

Restoration failures like this are often attributed to more esoteric causes, like lack of local plant gene pools in the plants used.  Believe me, even local populations aren’t going to survive poor installation techniques.

Thus, one of my recent graduate students conducted a meta-analysis of the applied restoration ecology literature to analyze it for horticultural content.  The results were not encouraging.  In Kathleen’s thesis abstract, she states:  “…careful selection and handling of planting stock, site and soil preparation, and rootball preparation, essential to increase survivorship of planted seedlings, are infrequently discussed in peer-reviewed restoration publications…Findings from this review support that restorationists either do not understand or are not providing important information to their peers, stakeholders, or the public on significant horticultural aspects of the restoration process.”

Now I know most of you are not restoration ecologists…but I’ll bet many of you are interested or actively involved in planting or maintaining native plant habitats, public greenspaces, degraded urban lots, etc.  The science behind gardening is just as applicable to these “wilder” areas as it is to home landscapes and gardens.


Failure of entire installation.  Note suckering from the roots – an attempt by the tree to establish a shorter crown.  (It’s easier to transport water to a short crown than a tall one, and suckers are often a symptom of root failure)

Organic farming study at – gasp! – a research university

There is a common misperception among some that university researchers are in the pocket of Big Ag (see June 11 and 13 posts). So here’s a link to an article in today’s Seattle Times about the benefits of organic farming from a study at Washington State University.  The research was published in Nature (one of the most revered of the scientific journals).

The Approach Graft

Seeing as this blog is called “The Garden Professors” it has been far too long since we’ve given you a lecture on a useful practice for your garden, so this week I thought I’d give you a little how-to demonstration on something called approach grafting.  Approach grafting is a technique that you could use to graft a tomato to a tomato (good if you want to use a disease resistant root with a non-disease resistant top — common in heirloom tomatoes), a tomato stem to a potato root (just a fun project), or an eggplant root to a tomato shoot (good for wet locations).

So here we go.  First, you need two plants that are about the same size, and you need to plant them in the same container as demonstrated below with a potato and tomato.  You will also need to strip off lower leaves as they may get in the way of the graft.


Above we have a young potato and tomato plant to be grafted.


In the above picture the potato and tomato plant have been planted in the same container and their lower leaves have been stripped off.

After the two plants are in the same container a small slice is made on each plant at the same height.  This slice will be, ideally, just a little bit deeper than the cambium into the center of the stem (you’ll be able to see the plants pith — in the center of the cut — it’s tough to see in the image here).


In the above picture the stem of both the tomato and potato are cut so that they can be joined together.

After making the required cuts on both plants the cuts are pushed together and wrapped.  We used parafilm to wrap this graft, but saranwrap, or even an elastic band would also work.


In the above picture the cuts are being joined.


Here the cuts are wrapped.

The next step is to wait until the graft “takes”.  This could take 3-5 weeks.  After a good strong union is formed the top of the potato and the bottom of the tomato plants are cut off.  Wait a few days to make sure everything’s working properly and plant the result in your garden.

Lunar control? Or lunacy?

Yesterday one of my dear skeptical colleagues sent me a link to a new article on lunar influences on plants (you can find it here).  Briefly, the authors argue that scientific evidence supports the concept of a lunar cycle influence on plants.  Interspersed within the discussion are references to seasonal and daily plant cycles, along with legitimate references to these verifiable phenomena.  (Had these references to circadian and diurnal rhythms been left out, the literature citations would have been rather paltry.)  Plants depend on these daily and seasonal cues for a variety of physiological and behavioral activities; lunar cycles have little obvious relevance to plants.  Nevertheless, “planting by the moon” is a belief system that has existed since ancient times.

This article is a great example of how pseudoscience insinuates itself with legitimate science.  Many of the references used as evidence for lunar effects on plants are of nebulous quality as they haven’t been reviewed by the scientific community; these include self-published books or lectures.  Furthermore, for every article that claims a lunar effect, I can find another discounting it entirely.  That being said, there are some legitimate papers indirectly linking lunar cycles with plant biochemistry.  Coincidentally, the lead author of one of these articles is a close friend and colleague whose research credentials are impeccable.

Here’s where the fascinating and complex nature of species interactions helps explain conflicting data.  Lunar cycles do affect certain species, including some herbivorous insects which are dependent on moonlight for feeding.  During the full moon, such insects feed more heavily and affected plant populations retaliate by altering the digestibility of their tissues. It’s likely that these biochemical changes have been erroneously attributed to direct lunar influence rather than herbivore defense.

To demonstrate direct lunar influence, one would need to study plants in an herbivore-free, controlled environment so that the only variable under consideration was lunar cycle.  Under such controlled conditions, would the same changes be noted over time if plants weren’t eaten by moon-managed insects?  Would you see changes if you modified the lunar cycle to make it longer or shorter (again without insects)?  Positive and repeated results would be necessary to establishing a role for lunar control.

As with so many other mystical explanations of natural phenomena, the real story is infinitely richer and more satisfying.

UPDATE: A peer-reviewed literature review on this topic has just been published. It’s well worth reading.

Baffling Daffs

It is daffodil season in the Northern Hemisphere, hurrah!  May their blooms shoo away the gray of winter! It is also the season where everybody and their mother writes something about the wonders of the genus Narcissus, so figured I’d join the fray, but with a bit of a chip on my shoulder…


Miss ‘Barrett Browning’ in the Hahn Horticulture Garden at Virginia Tech

I recently read YET ANOTHER article warning against mixing daffodil stems in with other cut flowers due to “harmful effects from the sap”. If stems are conditioned, that is, placed in warm water on their own for 12 to 24 hours, it’s supposed to be o.k. This is repeated in everything from floral arranging manuals to gardening articles, but they never say what exactly causes the problem. So I’ve combed through many resources, to find a specific study backing this up and identifying what compound is responsible.

Known:

1) There is such a thing as “daffodil picker’s rash” which has been reported in the journal of Contact Dermatitis  (Julian and Bowers, 1997).  The authors attribute this rash to the “crystals of calcium oxalate in the sap, in conjunction with alkaloids, [which] act as an irritant, and also cause the characteristic sores.”  Duly noted.

2) Said calcium oxalate crystals are found throughout the daffodil, in the bulb, stem, sap, flowers, etc. Micrographs show that these crystals are needle-sharp, and apparently very painful (I have not gotten up the nerve to give them a nom).  This is why deer and bunnies will not eat your daffs.

3) The list of alkaloids is fairly extensive (as with many other members of the Amaryllidaceae family), including masonin, homolycorine, and a real nasty one, narciclasine- which disrupts cell division (meiosis) much like colchicine.

4) Are daffodils poisonous? Yes. If you (or your cat) hunkered down and consumed an entire bulb, problems would ensue. But the calcium oxalate crystals are, perhaps, nature’s way of convincing you (or Mr. Twinkles) that this is not a good idea.

So is there really an effect and if so, what makes daffodil sap deleterious to the other flowers in the vase?  The study “Effects of Daffodil Flowers on the Water Relations and Vase Life of Roses and Tulips” by W.G. van Doorn appeared in the Journal of Horticulture Science. Dr.van Doorn found the mucilage (sap) was indeed to blame, with just one daff shortening the vase life of both the tulips and roses by almost half.  But what component?

He split out the alkaloid fraction and the sugar fraction of the sap, and then added them as individual components to the vase water.  He drew different conclusions as to the cause: the research indicated that the effect in roses is mainly due to the sugar and polysaccharide fraction of the mucilage stimulating bacterial growth. This clogged the rose’s vascular system resulting in bent neck. You’ve seen this before – the bud, yet to open, flops over, never to recover.

These same sugars didn’t impact the tulips negatively but the alkaloids sure did. Even touching the sap to the tulip foliage produced a yellow spot.  He was not able to distinguish which of the six alkaloids detected were responsible, but at least narrowed down the cause ( sounds like a job for a grad student!).

So there you have it. I feel better. Am off to pick a few daffodils (very carefully) to brighten my office.