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Keep surface dry & alkaline for fungal prevention

Posted by Strawberryhill 5a IL (My Page) on
Mon, May 27, 13 at 14:03

Here's a description on how black spot spores are transmitted: "The fungi that cause black spots overwinter on infected leaves that fall to the ground. The following spring, just as new leaves are unfolding, the fungal tissue in the leaves on the ground ripens. The surfaces of the spots split and minute, needlelike spores escape. The spores are carried about by wind and if they land on new leaves of a susceptible host they may germinate, penetrate the leaf tissue, and start a new disease cycle."

I can't find the optimal pH for black spots on roses, or diplocarpo rosae, but I found the optimal pH for its relative, diplocarpo mespili, or black spots on fruit trees' leaves.
Optimal pH for diplocarpo mespili is pH 4 to 7. The optimal temp. is 71 degrees to 78. Here's info. from University of Maine:

"As is true with most fungi, this fungus requires free water for infection to occur. The spores must be wet for at least 7 hours before they can germinate. A temperature of 65°F is best for spore germination and the disease develops most rapidly at about 75°F. Temperatures of 85°F and above inhibit the spread of the disease."

Either dry and alkaline, or VERY acidic would discourage fungal growth. Baking soda, at pH 9, discourages fungal growth. I also spray diluted vinegar on the black fungus on my shower curtain. Corn meal is reported in the canning site with pH 7.3, but when I tested it in red-cabbage juice, it's VERY ACIDIC at pH 3.5, more pink that peat moss at pH 4. Corn meal has zero salt, so it's better for the roots than milk or baking soda - both have salt.

Corn meal also supplies nitrogen to the soil, and it hosts Trichoderma fungi, the beneficial fungi that inhibits the pathogenic black spot species. Whole grain corn meal works best, the refined corn meal doesn't work.

Below is a picture Eglantyne, most prone to blackspot, dusted with WHOLE GRAIN corn meal before a rain. It's 100% clean the first year. The second year, I didn't dust with corn meal, and it got black spots in late fall, despite my alkaline soil, pH 7.7.

Also it helps to grow own-root roses, rather than grafted on Dr. Huey. Dr. Huey rootstock prefers it dry and alkaline, and GRAFTED roses broke out in BS in my last house of wet acidic clay, mulched with acidic pine bark (pH 4.5).

Eglantyne - no BS photo Eglantyne.jpg

Below is a link of the most tough, disease-resistant roses to grow. I have one hybrid tea grafted on Dr. Huey was in a bed topped with slightly acidic wet leaves, and that broke out in BS. However, the roses in a bed mulched with horse manure on DRY sawdust bedding, they stay clean in late fall, see below picture:

Here is a link that might be useful: Your most healthy and no-spray roses?

This post was edited by Strawberryhill on Mon, Jul 21, 14 at 15:31


Follow-Up Postings:

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RE: Keep surface dry & alkaline for fungal prevention

When you say sawdust bedding, are you talking about the stuff they sell at the pet store for bedding material or actual sawdust from say a wood shop. If it is actual sawdust then I have a goldmine next door.

grace e


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RE: Keep surface dry & alkaline for fungal prevention

Hi Grace: It's sawdust from a wood shop. The NPK of sawdust is 0.2 / 0 / 0.2 compare to NPK of horse manure at 0.6 / 0.3 / 0.5 .... Therefore fertilizer is needed if sawdust is used. I use Jobes tomatoe spike NPK 8-16-8 and push it DEEP down with a wooden post, since phosphorus (the middle number) stay put where's applied, move down maximum of 1" in one study.

I did another experiment this year: mulch half of Evelyn with horse manure at pH 7.5, and the other half with acidic cocoa mulch, pH 5.4. The result? Zero BS on the horse manure side, and a bit of BS on the cocoa mulch side.

See link below for NPK of any organic materials, it's a great reference:

Here is a link that might be useful: North Carolina State on organic nutrients


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RE: Keep surface dry & alkaline for fungal prevention

Awesome, thanks so much for replying. I live next door to a wood shop. Since they are family I don't think they'll mind if I clean up their shop for them :-). With the tomato spike did you do any additional fertilization.

Oh here is a question does the type of wood make a difference. Should I just stick with pine. (I already know no walnut, but what about other types)

Grace e


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RE: Keep surface dry & alkaline for fungal prevention

Hi Grace: Pine mulch is longest-lasting and makes good mulch. However, pH of pine bark is 4.5, even more acidic with rain water. That stuff is great to lower my alkaline soil, pH 7.7, for acid plants like azaleas that prefer pH of 5.5.

My roses are healthier with bigger blooms when the pH is slightly alkaline. When I bring the pH down to 6.5, they produce more blooms, but lesser quality with multiple buds per branch, resulting in smaller blooms, and harder to cut for the vase.

Best to check your soil pH before using pine bark. Other types of bark such as cypress or hard wood are neutral in pH. If the sawdust is really small, there's the risk of it blowing into your eyes. One person cleaned up sawdust made by termites, and got blind. I used peat moss one spring for my azaleas, breathe into my lung, and got pneumonia with many chest X-rays, bronchoscopy, and near $5,000 medical bill .... luckily insurance paid most.

See below for the woodchips that the stable used for their horse manure, much bigger particle than sawdust. It's the perfect size, and doesn't poke my feet like the large mulch that I got for free at the village's pile.


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RE: Keep surface dry & alkaline for fungal prevention

Last year I called the stable here and asked if they put lime in their horse manure, they said yes. I tested the wood chips & horse manure (picture above), and it's alkaline, blue in red cabbage juice (pH around 7.5). Last two years my roses were clean.

This year the stable stops liming their manure. I got the well-composted manure, it was too wet, didn't work well. Two weeks ago we came to get more manure. I was disappointed to see tons of mushroom in the bedding. They changed the bedding from dry wood chips to wood-shavings and straw (thin strips), very wet. I tested that stuff and it was slightly pink in red cabbage juice, pH around 6.8. No lime was added by the stable.

I mulched a few of my roses with that, they broke out immediately in BS. The bedding retained moisture too well, some of the roses' branches even got black canker buried with the acidic manure/bedding. I scraped off some today, will put dry and alkaline corn meal on top. The roses in front NOT mulched with the new horse manure are still 100% clean.

This post was edited by Strawberryhill on Tue, Sep 10, 13 at 11:37


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RE: Keep surface dry & alkaline for fungal prevention

My Samaritan (King Arthur) rose has a few lower leaves affected with black spots in our very humid weather. It's a BS-prone rose, mulched with acidic cocoa mulch (pH 5.8), but dry and fluffy. The result? A few leaves at the bottom infected with blackspots:

 photo KingbushSept.jpg

Compare that to my neighbor's roses. Hers are 100% clean, mulched with limestone (dry and alkaline). Her roses are in partial shade, with 4 hours of weak morning sun. Our zone is 5a, with a short hot summer, but rainy spring and fall.

I don't recommend mulching with stones for a hot and dry climate like CA ... the stones will also heat up roses in full-sun. Below is my neighbor's hybrid tea, 100% clean, fertilized with MiracleGro soluble, mulched with lime stones:

This post was edited by Strawberryhill on Thu, Oct 24, 13 at 9:44


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RE: Keep surface dry & alkaline for fungal prevention

In my last house of acidic clay, my mulching with acidic pine bark really hurt. Here's an excerpt from University of Georgia on thick pine bark mulch:

"Anaerobic respiration can occur producing acetic acid (vinegar), phenolic and alkaloid compounds toxic to plants. The pH may drop as low as 2.0, which causes nutrients to be flushed from the pine bark. These can also be toxic... Mold in the bark which repels water. Pine bark in dry piles may develop high fungal populations recognized by clouds of spores when disturbed. Once spread out and irrigated, a mold (mycelia) grows rapidly which repels water. Newly set plants may dry out and die. "

Note the above sentence: "Anaerobic respiration can occur producing acetic acid (vinegar), phenolic and alkaloid compounds toxic to plants." My putting vinegar to lower my pH 8 tap water was NOT GOOD. Leaves became wilted in the heat.

Vinegar (acetic acid) is toxic to plants, I get better result lowering my high pH tap water with soluble gypsum (calcium sulfate, with 17% sulfur) and sulfate of potash (with 23% sulfur),

This post was edited by Strawberryhill on Sun, Oct 13, 13 at 9:52


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RE: Keep surface dry & alkaline for fungal prevention

One advantage of using organics is it benefits earthworms and soil microbes. Chemicals, be it Bayer spray or chemical fertilizer can upset the flora of soil microbes, giving rise to pathogenic fungi.

Even gypsum (23% calcium and 17% sulfur, salt index of 8) caused rust on the metal scoop. It's corrosive and killed soil bacteria, resulting in rust and black spots when I applied too much on the surface.

Organic fertilizers nourish beneficial soil microbes. Here's an excerpt from the below link on organics fertilizers:

"Yum Yum Mix 2-1-1

Alfalfa Meal: Nitrogen; Vitamins-A, B, E, carotene, thiamine, biotin, pantothenic acid, niacin, riboflavin, folic acid, choline; 16 amino acids, co-enzymes, sugars, starches, protein fiber

Cottonseed Meal: Nitrogen, Phosphorus, Potassium

Kelp Meal: Nitrogen; Potassium; Vitamins-A, B, B2 , C, calcium, pantothenate, niacin, folic acid; minerals-barium, boron, calcium, cobalt, copper, fluorine, iron, magnesium, manganese, molybdenum, nickel, sodium, strontium, sulfur, zinc; 17 amino acids

Greensand: Iron, Potassium, Silicate, Phosphorus, 30 trace elements

Rock Dust: Calcium, Sulfur, Magnesium, Boron, Cobalt

Rock Phosphate: Phosphorus, Calcium, Trace Elements
Humate: Salts of Humic Acid ��" improve soil characteristics and aids in releasing other nutrients to plants in usable forms

Dry Molasses: Carbohydrates, Sugars, Trace Elements ��" feeds and attracts beneficial soil organisms."

*** From Strawberryhill: When I research on endo and ecto mycorrhiza fungi that access nutrients for plants, they thrive at pH below 7. The sugar in molasses feed these fungi that help plants to utilize nutrients in soil.

Here is a link that might be useful: What's hiding in your organic fertilizers?


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RE: Keep surface dry & alkaline for fungal prevention

now I better keep my sweet tooth away from Molasses and feed my roses then, so nice to know that your research for growing healthy & organic roses, we are lucky to benefit from that. Thank you very much, you are very generous to share info with all of us rose lovers.
I just bought Plantation brand of Blackstrap, un sulphured, sodium 10mg, potassium 600mg (17%) sugar 11g (4%), Calcium 20% and iron 20%,net 15 FL, that shall lasts a long time, apply to lots of roses.


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RE: Keep surface dry & alkaline for fungal prevention

Hi Seaweed: Next summer I'll test molasses as fertilizer during high heat. The chicken manure is too salty & high-nitrogen for temp. above 80 degrees.

I rooted roses from cuttings and also grew roses from seeds. Good drainage, and dry upper soil surface is a must to prevent molding. I found an Australian link that describes the soil-mix for different purposes:

Here's an excerpt from the below link:

•Seed mix: Vermiculite, coarse river sand (2:1)
•Cutting mix: Perlite, coir (9:1 in winter or 5:1 in summer)
•Potting mix: Commercial potting mix with trace elements. Free draining mix of composted pine bark and coarse river sand (90:10 or 95:5). Has a high air filled porosity (15 to 20%) for good aeration and drainage. The potting mix is pasteurised in the nursery before use

Here is a link that might be useful: Australian Horticulture - Growing Media


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