Research that gardeners should appreciate!

Today I received my November 2012 issue of Arboriculture and Urban Forestry.  This is one of the few peer-reviewed journals that generally has information of immediate value to gardeners and landscape professionals as well as academics.  This issue contains an article entitled “Evaluation of biostimulants to control Guignardia leaf blotch (Guignardia aesculi) of horsechestnut and black spot (Diplocarpon rosae) of roses.” (And before you ask, no, I can’t attach the article or link to it.  You’ll need to read it in the journal itself or wait for a year when the organization makes it available to everyone.)

Anyway, this study looked at eight different self-identified biostimulants, including Superthirve (which every gardener must have heard of by now).  In addition to Superthrive, the other products tested were Maxicrop Original, Resistim, Bioplex, Fulcrum CRV, Redicrop, Crop Set, and Systhane. Purported active ingredients within this group include seaweed extract, molasses, vitamin B, and Lactobacillus fermentation product.

And the $64,000 question – did they work?  Here’s the authors’ summary: “Irrespective of pathogen or concentration applied, none of the biostimulants used in this investigation provided a significant degree of Guignardia leaf blotch or black spot control compared to water-treated controls.”  In other words, you can expect the same results by spraying your black spot-infested roses with water compared to any of these biostimulant products.

The authors end their article with a caveat sure to warm the cockles of every Garden Professor’s heart: “Results of this study indicate that where independent scientific data are not available to support the pathogen control claims of the manufacturer, then using an unevaluated biostimulant for this purpose is not recommended.”

(I’m glad this article is finally out. I was one of the peer reviewers for it, and I’ve been wanting to share the results on the blog ever since I read it.)

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Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and a Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - "The Garden Professors" Facebook group - Books:

6 thoughts on “Research that gardeners should appreciate!”

  1. This is unsurprising, but interesting nonetheless.

    On an unrelated note, I do wonder about something I’ve often seen in your posts: identifying yourself as a peer-reviewer. I was under the impression that this is a confidential process. Maybe I am mistaken?

  2. That’s a very good point and well worth explaining. AUF has a double blind process for manuscript review. Reviewers don’t know the authors and the authors don’t know the reviewers. Once an article is published, however, that confidentiality is no longer necessary (though of course you could keep it secret). I’ve had colleagues tell me post-publication that they were reviewers, and as far as I know this is not a problem. (If it IS a problem, I’m sure I’ll hear about it now!)

  3. Interesting info and I’m surprised folks try to use such things other than what they were originally intended for. Of course in your list the only one I know of is Super-thrive for which has been round forever it seems.

  4. Interesting link Linda. I haven’t used Superthrive since the late 1970s, but when I did I found that using just a couple drops to a gallon of water (or whatever the instructions said for transplant shock prevention) seemed to work and stimulate plant growth, but it you used too much, the plant would stay stuck in neutral. However I stopped using it in 1981 when I found out more about mycorrhizal & beneficial inoculents , though there were’nt many producing such things for the public back then. I haven’t used any transplant B-1 miracle whatever for years.

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