Update #2 - Re: Using cornmeal as a plant fungicide

nandina(8b)April 10, 2003


Many of you have been following the various postings on GardenWeb regarding our experiment using cornmeal/ground corn as a plant fungicide. Let me stress that this is still an experiment which is showing promise and needs further testing. Please report your successes, failures, observations, etc. on this thread.

Here are a few guidelines that may help you:

1. Please use only grocery store purchased cornmeal in vegetable gardens.

2. This experiment uses only cornmeal/ground corn. I have no idea if other corn products such as masa harina, grits, etc. will give the same results. Your reports/results on the subject will be of great interest, especially to those gardening in other countries.

3. How to use cornmeal as a fungicide? It is easy. Just scatter a handful of it lightly around any plant which is prone to fungus or mildew problems beginning in the early spring. Repeat this treatment once a month. Try it on roses for blackspot, tomatoes, hostas, zinnias, hollyhock rust, lawn problems such as Red thread, Brown patch, Southern blight, etc.

4. DO NOT USE cornmeal as a fungicide on young seedling growth to prevent damp-off. Recent reports indicate that this use of cornmeal is harmful to the very young seedlings.

Wait until the plants have grown strong enough to be planted in the garden and then begin a cornmeal treatment, if needed.

If you post your observations would you please give the name of the closest large city near you.


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Thank you, Nandina. But could you cite some sources for the information that cornmeal is harmful to very young seedlings? I wonder if that isn't corn gluten meal, rather than ordinary cornmeal.

    Bookmark   April 10, 2003 at 4:10PM
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I have been trialing cornmeal every which way. This winter several posts appeared on one of the Forums stating that young seedlings treated with cornmeal to prevent damp-off...died off. So, this year (Note: I have some 50 years of growing and nursery experience) I divided my seedlings into two lots, treating one lot with cornmeal. At least 60% of the seedlings died and the rest very slowly developed true leaves and are still only about 3-5" tall. The untreated lot of seedlings matured easily and are planted in the garden showing good growth. It is on this basis that I suggest not using cornmeal on young seedlings to prevent damp-off. Perhaps others have had a different experience and hopefully will post. That is the purpose of this thread....to exchange information and learn from each other's experiments with cornmeal.

    Bookmark   April 10, 2003 at 8:03PM
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Thank you for the information. I asked my question in all seriousness because, in my 65 years of gardening experience, I had never come across any information that indicated that common old cornmeal was anything but good stuff for young seedlings. And there are plenty of people who recommend it for use against dampoff.

    Bookmark   April 11, 2003 at 2:45PM
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I used cornmeal on my roses - scattered half cup around each rose a month ago, may be 5 weeks ago. Almost all of my roses have black spot, even those that usually get black spot much later. So far this experiment proved to be very disappointing for me.

    Bookmark   April 14, 2003 at 12:05AM
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Some corn products may inhibit or prevent seedling growth.

It is thought that if the cornmeal contains corn gluten, it can retard or prevent root development in seeds or seedlings. This is a useful discovery if used for weed control.

Here's a link to some research on the reason that some cornmeal may prevent germination or be harmful to young seedlings.

Happy gardening......and may all your weeds be wildflowers!

Here is a link that might be useful: Research on corn gluten

    Bookmark   April 15, 2003 at 10:31AM
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dchall_san_antonio(8 San Antonio)

Micimacko, your experience is interesting. Have you used compost around your roses in the past? Are you experiencing other pest problems this year? Have you fertilized or sprayed anything this year?

I had to run out and look at my neighbor's roses just now. She throws corn meal at everything from a distance of about 10 feet. So her rose leaves are covered with corn meal. Last summer she bought 20 roses for $20 thinking she couldn't go wrong. 19 of them survived and many are blooming right now. Some have grown considerably since the last corn meal application. Interestingly, some of them have powdery mildew on the new growth since the last corn meal application. I did not see any PM on any of the leaves with CM on them, but from there up, every leaf had it on one plant. I did not see any black spot on any of the plants. We're figuring she got rose varieties that everyone (except her) knew were highly susceptable to PM.

So I came back to look at my roses. One (of 5) has PM on about 6 leaves. I'm not going to do anything right away. I don't see any black spot except the black spot leaves I left on the plants when I pruned (as an experiment). I've been scattering corn meal under the roses monthly since mid Feb. Next scattering is due May 1st.

Another interesting observation is that one rose did not grow at all last year. It leafed out after pruning but stayed at the height of pruning. This year I did not prune it at all leaving the black spotted leaves on it. It is now almost as tall as the tallest of the roses on one cane of new growth.

I'd also like to update my aphid/cornmeal report. To summarize, ever since I started with corn meal (Feb, 2001) I have not had any aphids on my roses. In the 8 years prior, my roses were blanketed with aphids like everyone elses. Now I've been claiming zero aphids for 2 years. This year I watched extremely closely and found one stem with about a dozen aphids on it a couple weeks ago. Within a week they were all gone, so I'm still declaring victory over aphids with the corn meal treatments. I realize there is no simple explanation for the aphids being gone having anything to do with the corn meal on the dirt. Still, that's my observation. In the two previous years, I applied corn meal in Feb. This year I'm doing it monthly, as I said above.

    Bookmark   April 22, 2003 at 1:40PM
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If your looking to kill everything I have found that vinegar does just that.I put it in a spay bottle and spay where needed.Just make sure it aint going to rain for a couple of days.

    Bookmark   June 16, 2003 at 8:10AM
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I had some lawn customers on Long Island with terrible fungus problems last summer. Tried curative chemical app.Bayer fungicide
with poor results. I plan to try cornmeal app.this spring.
I will post results.Hopefully it will work,I am looking foreward to trying this.

    Bookmark   February 7, 2012 at 7:07AM
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I have liriope crown rot which did not respond to either Kphyte or Bayer fungicides. I did try the cornmeal with skepticism. but within weeks it was under control. I would really like to know how this works - all I can say it worked for me on liriope.

    Bookmark   September 20, 2013 at 11:36AM
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To wild acres: First, it has been interesting to review the sudden reappearance of the discussions re using 'cornmeal as a plant fungicide'. Thanks for your Liriope report and your desire "to really know how this (cornmeal) works"? To answer this question is to refer back to the original university studies with peanuts for a possible answer. They reported that cornmeal encourages the growth of Trichoderma fungus which feed on mycelium and sclerotia of Sclerotina minor, Sclerotina rolfsii and all Rhizactina species. Since that report we have received enough information to add Pyricularia grisea (gray leaf spot) to the list and now, thanks to your report, possibly Phytophthora palmivora (Liriope crown rot) to be trialed and tested.

The bottom line to all this is:
If cornmeal does control this or that fungus, we have to test for and identify the responding fungus using scientific methods. To date academia is sputtering around this subject mostly in a negative manner. Those of us who have been testing know that cornmeal does control certain types of fungus. This would be an interesting and badly needed doctoral project.

My final thoughts...Got a plant fungus? Try tossing some cornmeal on and around the problem, misting it lightly with water. It may control the fungus, repeated monthly, or it may not. If it does try to figure out the name of the controlled fungus and if it fits into any of the varieties listed above.

It is always interesting to read the comments of others on this subject as they use the 'trial method' experimenting in their own backyards.

    Bookmark   September 24, 2013 at 10:06AM
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jamac80(z9 TX)

I have gotten leaf blotch on my amaryllis for the first time ever. There are over 100 bulbs scattered about in the two affected beds and I'm not keen on digging each and every one up to treat or throw out. They are in a bed of antique roses, crinums, lilies, paperwhites, a gardenia, glads, and cannas. Only the amaryllis are affected, so far.

My experiment is to try a combination of horticultural corn meal and Consan. Day 1, I broadcast the corn meal by hand. I covered all of the amaryllis leaves and everything else in the bed. Day 2, I sprayed the strained liquid from soaking corn meal over everything. Day 3, I cut away as many of the infected leaves as I could from Bed 1. If it appeared that the bulb was too far gone, I dug it up. I then sprayed the whole area, under the leaves, etc, with a mixture of more corn meal "extract" and Consan Triple Action 20. I ran out of daylight to do this to Bed 2 so the leaves stayed on the plant and I just sprayed with the corn meal/Consan mixture.

Will let you know how it transpires. All suggestions are welcome!

    Bookmark   April 22, 2014 at 9:18AM
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concretenprimroses(4B NH)

Last September I put cornmeal on the new growth of hollyhocks that I had ripped down due to mildew or rust. The new ones were fine, but of course didn't bloom. This year I put corn meal on the plants and soil around them a month ago, and just did it again today.
Today I also put corn meal around the base of 2 tomato plants. I have had powdery mildew on my tomatoes the past 2 summers. I just can't bring myself to use poison. If it doesn't work, I'm going to try tomatoes in pots. I might also try the aspirin in water spray, but want to do more research first.
I'll let you know what happens!

    Bookmark   May 18, 2014 at 11:42AM
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concretenprimroses(4B NH)

I have beautiful holly hocks, no rust.
The tomatos are not as bad as last year, but its not been as wet either. Today I sprayed the tomatoes with sodium bicarbonate and water and took off all the bad leaves. We'll see how it goes.

    Bookmark   July 8, 2014 at 10:05PM
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Imapepper(zone 8)

Thumbs up for using water ground cornmeal under crepe myrtles to prevent mildew on leaves. Used it 3 years ago and haven't had to use it again. Also I had leaf-rollers(worms) on my Canna Lillie's and read on the forums that flour would stop them. Sprinkled them 3 years ago and so far no more leaf-rollers. So nice to find things that work. Cornmeal will keep seeds from sprouting.

    Bookmark   July 29, 2014 at 5:48AM
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mikebotann(8a SE of Seattle)

So far Nandina has been the only one using control lots. In the absence of that, the information is useless conjecture at best.
Plus, we're only talking cornmeal here as a fungicide, not other methods.
You also have to be specific as to where the cornmeal is applied. Just on the leaves, just on the ground, or both....with control lots, of course.
Don't they teach the scientific method anymore?

    Bookmark   December 2, 2014 at 8:38AM
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