Why dusting with alkaline corn meal works?

strawchicago(zone 5a)May 27, 2013

Keep the surface of leaves either dry and alkaline, or VERY Acidic ... both suppress microbes. Here's dusting with cornmeal, after 7 days of non-stop rain in late fall, zone 5a. Radio Times rose below has a reputation of black-spot-prone. It's 100% clean, dusted with whole-grain cornmeal, very acidic at pH 3.5.

At the same time, my Impatient annual flower came down with black spots in 7 days of non-stop rain:

See the abstract below:

"The influence of pH on the two principal decomposer groups in soil, fungi and bacteria, was investigated at Rothamsted Research in the United Kingdom. ...The growth-based measurements revealed a fivefold decrease in bacterial growth and a fivefold increase in fungal growth with lower pH. .. Below pH 4.5 there was universal inhibition of all microbial variables. "

See below link on how to dust your roses, plus the ground with Whole-grain cornmeal, pH 8. It's sold for $2 to $3 per lb. at the Organic Section of grocery stores. Walmart has it as Bob's Mill brand. The advantage of corn meal is it has no salt. Milk, baking soda, or potassium bicarbonate (Green Cure) all have salt. Corn meal also supplies nitrogen to the soil, and host the beneficial fungi Trichoderma that suppress the pathogenic black spot fungi.

Here is a link that might be useful: How to dust roses with whole-grain corn meal

This post was edited by Strawberryhill on Mon, Jul 21, 14 at 15:16

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This is the published, reviewed scientific paper which discusses the ability of Trichoderma viride to supress blackspot on roses.

Title: "Influence of phylloplane colonizing biocontrol agents on the black spot of rose caused by Diplocarpon rosae"

Published in: Journal of Plant Interactions, Volume 2, Issue 4, pages 225-231, (2007)

Authors: Muthusamy Karthikeyana*, Ramanujam Bhaskarana, Subramanian Mathiyazhagana & Rethinasamy Velazhahana

Abstract: "An attempt was made to study the biocontrol efficacy of antagonistic microorganisms in phylloplane of rose cv. Edward to manage the black spot (Diplocarpon rosae) disease. Eight antagonistic microorganisms were tested in vivo against the black spot pathogen. Among these, Trichoderma viride and Pseudomonas fluorescens pf1 reduces the mycelial growth significantly. These two biocontrol agents were evaluated for their ability to induce defense-related enzymes and chemicals in plants. Increased activity of phenylalanine ammonia lyase (PAL), peroxidase (PO), polyphenoloxidase (PPO) and total phenolics were recorded in all the biocontrol agents treated leaves. P. fluorescens Pf1 recorded early and increased synthesis of the entire defense-related enzymes and total phenol within 6 days. The application of biocontrol agents induced the defense-related enzymes involved in phenyl propanoid pathway in addition to direct antagonism, which collectively contribute for enhanced resistance against invasion of Diplocarpon rosae in rose."

    Bookmark   June 2, 2013 at 11:55PM
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strawchicago(zone 5a)

Thank you, Henry, for that research paper on Trichoderma in suppressing black spots in roses. I always respect the info. you give. I checked, you are a retired chemistry professor from The University of Akron (1965-1993), and obtained your Ph.D. in chemistry from Michigan State University (1965).

BTW, Henry, I worked at Lansing for 1 year. My brother got his Doctor of Veterinary Medicine at Michigan State.

Below is the link to Henry's site on General Rose info., plus Rose Hybridizing, and his chemistry publications.

Here is a link that might be useful: Henry Kuska's site on roses hybridizing

    Bookmark   June 3, 2013 at 5:03PM
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If cornmeal works (and I doesn't work for me), it find it hard to believe it has anything to do with Trichoderma.

Trichoderma genus fungi are *everywhere*. Among those who grow mushrooms, Trichoderma are the most common contaminant, the much feared "green mold". Cornmeal is likely to contain Trichoderma spores, along with spores of countless other organisms. And so would almost any agricultural product. Cornmeal feeds Trichoderma, but so would many other organic materials. Cornmeal also feeds diplocarpon rosae..

    Bookmark   June 10, 2013 at 4:46PM
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strawchicago(zone 5a)

There are other factors besides corn meal (keep the surface of leaves dry and alkaline, or extremely acidic) ... such as how much potassium the root can pick up to fight diseases. Without potassium, plants have weak stems and thin leaves, more susceptible to fungal invasion.

Are your roses grafted on Dr. Huey? Grafted roses have problems picking up water and nutrients, since it has to pass UP a restricted bud union. That bud union could be damaged by dryness in stores, winter, or acidity in soil.

I bought Gruss an Teplitz, the parent of Dr. Huey, just to do experiments. Gruss an Teplitz is famous for black spots and mildew. Gruss is the ONLY ROSE in my pot ghetto of 16 roses, that come down with severe aphids infestation. Gruss has skinny tender stems, symptoms of potassium deficiency. I gave Gruss Sulfate of Potash, NPK 0-0-50, and it didn't help, still weak stem.

Dr. Huey, as the offspring of Gruss, doesn't pick up potassium well either. Potassium is needed to fight diseases. That's why GRAFTED-ROSES on Dr. Huey is more susceptible to diseases.

All my 52+ roses are own-root, last year I didn't bother to dust them with corn meal, just a touch of black spots on Eglantyne. This summer I gave Eglantyne potassium via Sulfate of Potash, when the buds are tiny.... it's 100% clean in this month's rainy weather.

Below is hybrid tea Sweet Promise, own-root, taken next to hybrid tea, Firefighter, also own-root ... both are clean, zero diseases. Picture taken end of May:

This post was edited by Strawberryhill on Mon, Jul 21, 14 at 15:17

    Bookmark   June 10, 2013 at 5:22PM
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this rose is a tough one, end of Spring, cut half length of canes, now it comes back with nice scent, good colour & shape. I only put some of compost & amend to increase its nutrition, it is a easy rose to grow.

    Bookmark   September 10, 2013 at 9:27PM
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strawchicago(zone 5a)

Hi Seaweed: I love that picture! What's the name of that pretty rose? It looks very healthy with compost. Thanks in advance for the info.

    Bookmark   September 10, 2013 at 9:36PM
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strawchicago(zone 5a)

HMF has a feature called "Q & A Forum" where you can search the comments in HMF by key words. I clicked on that "Q & A Forum" tab, and search for "corn meal" and found this post:

Reply of 4 posted 6 OCT 05 by texasmorningglory

"I don't know if this will help you or not on the blackspot but it works for me..... I use only organic methods with my roses, mulch well, feed with rose-glo and I put whole ground cornmeal which you can purchase at your local feed store inexpensively around the rose bushes if they show any blackspot problems. I live in hot humid South Texas, and this works well for me. I never spray my roses. "

Another post in HMF:

Reply of 22 posted 16 MAR 07 by William

I talked with a microbiologist about black spot and she told me to try coarse ground corn meal. She said by accident she found it to kill the fungus in the ground. Sprinkle liberally as it will not harm the roses. If this works it will indeed be a find for natural remedies.

This post was edited by Strawberryhill on Sat, Sep 28, 13 at 22:28

    Bookmark   September 28, 2013 at 9:59PM
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JessicaBe(5-6 Central Ohio)

How often do you put whole ground corn meal on? This is very interesting because I don't spray at all and my HT and Floribunda defoliated alot this year, my HT is growing leaves again but the Floribunda has not recovered.

    Bookmark   October 22, 2013 at 9:38AM
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strawchicago(zone 5a)

Hi JessicaBe: I applied cornmeal only once this year in mid September. It took away Gruss an Teplitz's mildew, plus he has only 2 BS-leaves when frost hit last night.

IowaGirl asked the same question in another thread, so I'll re-post the answer here:

Two years ago we had the wettest summer, 49" of rain. In that 7 days non-stop rain, mid-Sept., I threw corn meal at the base of the bush, getting lowest leaves dusted and the ground. Early Sept is the best time to start dusting in my zone 5a.

I did that before an 6 hours-rain. If the rain washes the cornmeal off, I dusted again. In between rains, there's a breeze that dried the cornmeal, and made it stuck. I kept 10 Austins clean, including Eglantyne.

The second year I did not dust whatsoever, and Eglantyne had blackspots. The rest of Austin roses were clean, thanks to the lime in horse manure and recycled wood chips (has fungicide).

Frederic Mistral is still clean before frost hit last night Oct. 21. What I like to experiment is to sprinkle some crushed limestone on the ground. Lime-pellets is expensive, plus raising the pH fast ... which I don't want to use. Crushed limestone is cheaper, sold for $2.49 per bag, and raises the pH very slowly. See picture of my neighbor's hybrid tea, 100% clean. She mulched with lime stones. But her roses are in partial shade & morning sun, so the limestones don't heat up in summer:

    Bookmark   October 22, 2013 at 7:02PM
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strawchicago(zone 5a)

Dusting corn meal on leaves makes the surface too acidic for fungal growth, since the pH of corn is 3.5, not 7.3 as reported in the canning site. On the ground corn meal holds moisture too long, and harbor pests. Other moisture-holding components: peat moss, Turface, NAPA floor-dry, kitty litter (mushy when wet, used for sandy soil).

Below is a link that detailed the pros and cons of moisture-soil-holding additives, with pictures of the products (Expanded clay aggregates, Haydite (expanded shale), Turface, NAPA floor-dry, and Lava).

Here is a link that might be useful: Pros and cons of soil additives

This post was edited by Strawberryhill on Mon, Jul 21, 14 at 15:20

    Bookmark   November 23, 2013 at 3:16PM
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