Deconstructing the cornmeal myth

Back in June of 2010, I wrote about an online column that recommended applying cornmeal as an antifungal soil amendment. (Important note: we are not talking about corn gluten meal. Just cornmeal.) The upshot of the post was while some gardening personalities extol the use of cornmeal to kill soil pathogens like Rhizoctonia and Sclerotinia, no published science supports the practice.  The post was effective in encouraging the author of the referenced online column to update her information, but the controversy didn’t die. In fact, new comments have been added to the original post on a fairly consistent basis, mostly in the form of personal anecdotes or angry rebuttals. Some commenters, however, have tried to carry on rational discussions, so today we’re going to look at cornmeal from a slightly different angle: what effect does it have on microbes in general?

To start, let’s look at the Stephensville, Texas research that’s most often highlighted by cornmeal proponents.  There’s no peer-reviewed work published on this specific research, but in an online copy of the Texas Peanut Production Guide I found a paragraph referring to "Biological Control of Soil-Borne Fungi." Here it is in its entirety:

"Certain fungal species in the genus Trichoderma feed on mycelium and sclerotia of Sclerotinia minor, Sclerotium rolfsii and Rhizoctonia spp. All peanut fields in Texas tested to date have natural populations of Trichoderma. For several years, tests have been conducted in Texas using corn meal to stimulate Trichoderma development as a way to control the major soil-borne disease fungi. When yellow corn meal is applied to fields in the presence of moist surface soil, Trichoderma builds up very rapidly over 5 to 10 days. The resulting high Trichoderma population can destroy vast amounts of Sclerotinia, Sclerotium and Rhizoctonia. This enhanced, natural biological control process is almost identical to the processes that occur when crop rotation is practiced. The level of control with corn meal is influenced by organic matter source, soil moisture, temperature and pesticides used. Seasonal applications of certain fungicides may inhibit Trichoderma. Testing will continue to determine the rates and application methods that will give consistent, economical control."

And that’s all there is on the topic. Most scientists would conclude that further testing was inconsistent and the researchers abandoned their efforts without publishing anything further. But this summary is at least a starting point, though it contains no data, references, or even authors.

First, there’s no argument that Trichoderma is a powerful antagonist of some nasty pathogenic fungi. Likewise, cornmeal most certainly can encourage the growth of Trichoderma, both in the lab and the field.  But cornmeal also encourages the growth of many other fungi – in fact cornmeal agar is commonly used for culturing fungi in the lab. So what about those three pathogenic fungi mentioned in the Texas peanut guide? Do they like cornmeal?

Indeed they do! Published research (about 20 or so articles) shows that cornmeal (not cornmeal agar) has been used to enhance growth of Rhizoctonia fragariae, R. repens and R. solani, Sclerotinia sclerotiorum and S. homoeocarpa, and Sclerotium rolfsii. In some cases the pathogens became more virulent in the presence of cornmeal.

Cornmeal is nothing more than a carbohydrate-rich resource that can be used by many microbes. If you happen to have a lot of beneficial fungi in your soil, cornmeal will feed them. If you happen to have pathogenic species in your soil, cornmeal will feed them too. So it depends on what fungi are already living in your lawn, vegetable garden, or rose bed on whether cornmeal will help, or just make disease problems worse.

The best thing to do – as the paragraph from the peanut guide suggests – is to mix things up a little in your landscape. Use mixtures of lawn grasses rather than growing a monocultural turf. Rotate plant placement in your vegetable garden every year. Add a microbe-rich organic mulch to your rose beds. Natural methods will keep pathogens in check much more effectively than a hyped-up home remedy that’s anything but antifungal.

5 thoughts on “Deconstructing the cornmeal myth

  1. I went point by point over the issues I have with this point until I realized I was just repeating the same comments I made last time so I deleted them. Summary as I see it.
    1. Someone on an internet content mill misquoted the Dirt Doctor video about cornmeal being an antifungal (I saw the video and I remember him talking about trichoderma and not claiming it was an antifungal. I don’t follow his site or videos don’t know what he said in others.)
    2. You wrote an article trying to dispell the myth that cornm
    19e0
    eal is an antifungal. You win. Those of us that use cornmeal don’t consider it an antifungal. I might say use cornmeal to treat plant disease when I’m too lazy to spell out the mode of action but I wouldn’t claim it was a fungicide.
    3. People like me came here trying to correct some of the things you said which were caused by you arguing points against an article on about.com that had a lot of errors.
    4. Your updated post continues to try and show cornmeal has no potential for application when it comes to plant pathogens which is not the same thing as proving it’s not a fungicide.
    I’ve previously posted links to other published and unpublished articles that shows there is at the very least there’s some potential.
    You said that trichoderma exists in all soil.
    You understand that trichoderma has been shown to control and/or prevent other fungal pathogens.
    You agree that cornmeal can stimulate the growth of trichoderma.
    Instead of coming to what I would consider a more reasonable conclusion that there might be some merit in cornmeal that could use further study but there isn’t enough basis for you to recommend it… you just want to argue against cornmeal being an antifungal.
    Compost is frequently used for bioremediation as well as for the control of plant pathogens. There have been many studies on the subject. Compost is not an antifungal agent. I’ve applied hundreds of lbs of compost to my lawn and it helped with disease. Cornmeal did too and it only took 10′s of lbs.
    If you had a dish with cornmeal agar and 50% volume R. Solani and 50% volume of trichoderma I would expect at some point that the tricoderma population would have increased in relation to the R Solani. Wouldn’t you? Seems like the most likely outcome. Fill an aquarium with 100 sharks and 100 sea lions you’d wind up with a tank of some fat sharks.
    I just don’t understand how you can post what you did and keep arguing that cornmeal isn’t an antifungal. It seems to miss the whole point and you imply there’s no scientific basis for the role of cornmeal in treating plant disease which seems disingenuous at this poing.
    I thought we were having a reasonable discussion last time. I’m not so sure now. I’m not sure if we will after the next thing I say but I have a bad habbit of being blunt and direct if I think the ultimate result is beneficial for most involved.
    In one of your comments you mentioned how sometimes researcheers/academics will let a paper/study fade away rather than update it to show there were errors. I think that’s what you’re doing here. Your last post on the subject was just plain wrong on so many levels. A ton of misinformation. Likely because it was directed at that about.com post which was also very wrong. Garbage in, garbage out.
    That last post maybe was very popular on the site, it got a lot of comments compared to other posts on here. Maybe that contributed too. You don’t want to say there were parts of that post that were wrong so you keep defending it. You jump to quite a few conclusions above trying to do so.
    I don’t think there’s any point going through it line by line pointing it out.

  2. In response to my original posting, Howard Garrett (aka the Dirt Doctor) states on his blog “Dr. Joe McFarland ran the research station in Stephenville that discovered the anti-fungal properties of cornmeal due to the impressive control provided by the tricoderma fungus in the cornmeal. That cornmeal works is irrefutable.” It’s pretty clear to me what he’s claiming, and it’s nonsense.
    You can read it for yourself here: http://www.dirtdoctor.com/Cornmeal-Controversy-Newsletter_vq4042.htm.
    While there may be “some potential” for cornmeal applications as you suggest, there is no demonstrable, consistent effect in treating plant pathogens. University faculty, especially those of us in Extension, will not recommend any product or practice which does not have some solid basis in published, peer-reviewed science. Cornmeal doesn’t meet that standard.
    Along these same lines I need to point out that in Washington state, at least, cornmeal is not registered as a pesticide. In any state, it’s illegal to apply unregistered products for pesticidal purposes on other people’s property (you of course can do so in your own landscape).
    Cornmeal is a nutritional resource for Trichoderma, which has demonstrated antifungal properties. That makes Trichoderma a biological control agent. It doesn’t make cornmeal a biological control agent. This would be analogous to suggesting the agar used to grow Bt controls mosquito larvae.
    Cornmeal is also a nutritional resource for all kinds of fungi, including the plant pathogenic species that Trichoderma can control. So applying cornmeal might make the pathogens grow better, or the Trichoderma – just like applying fertilizer to your lawn can make both weeds and turf grow better. Application of cornmeal depends on a lot of different variables, including what fungal populations are in the soil. The results are a crapshoot.
    Compost contains many microbes, some of which are antifungal. It’s a living system. Cornmeal is not. It’s simply a carbohydrate-rich organic material.
    Looking at my original post as well as this newer one, I can’t find anything I said that constitutes misinformation. Since none of my colleagues have corrected me publically or privately, I’m continuing to stand by what I said. If and when the science changes on cornmeal as a fungicide, you can be sure I’ll update my recommendation.

  3. All I know is after reading an article in Bottomline about a Texan man listening to a discussion somewhere along these lines on a radio gardening show, and him getting the bright idea to soak his toenails in warm water and cornmeal and it curing said fungus that he’d had for 27 years, when I tried it on my toenail fungus, it worked for me too.

    I believe the original suggestion was for fighting powdery mildew on roses….

  4. There is an antifungal protein in corn seed, zeamatin. I do not know its specificity as a fingucide, but perhaps works nicely o
    n some people’s toes. It then is curious about corn meal agar used as a substrate for fungi growth. Perhaps zeamatin does not survive autoclaving intact or is preciptiated and filtered out.

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