Powdery mildew - most effective fungicide?

16 years ago

I would appreciate recommendations as to the most effective fungicide against powdery mildew. I have never, ever seen such a horrible infestation of PM in my garden. Last spring when almost everybody was hit with PM in the eastern part of the country, my yard somehow escaped. But now I see it all over, even on roses that I haven't heard to be suspectible to PM. I must act fast otherwise my promising spring flush is over.

For prevention I used Wilt pruf kind of sprays on the few PM prone bushes like Clotilde Soupert in fall. Once, many years ago I used the Cornell formula on Zephirine Drouhin. But right now there is nothing to prevent, PM is here everywhere.

For a week the forecast was rain rain and rain again so I hoped that would wash away PM. But we hardly got any rain, so I decided not to wait any longer but act. Suggesstions? Would Tebuconazole be as effective as Bayer claims ti to be against PM? If not, what else is effective?

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Comments (12)

Jean Marion (z6a Idaho)
16 years ago
How many roses do you have? What percentage have PM? Are there a couple that seem impervious to PM?
hartwood
16 years ago
When I was having a horrible time with PM last fall, a dear rose friend of mine (who is my 'go-to' guy with all questions of a chemical nature) told me to use Systhane.

Connie
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Thank you, rhizo_1 (North AL) zone 7. Let me respond point by point: . "P., baking soda is sodium bicarbonate, not calcium bicarbonate (whatever that is). Sodium bicarbonate really does work." I meant sodium; I don't know how calcium got into my head! . "I worry a little about your prescription for the vinegar. It's very important that the dosage be accurate or leaf tissue can be burned. I also think that a warning about the very real effect that 2 or 3 T. of vinegar/gal. of water can do to the soil pH if carelessly watered in on a routine basis is important." My precscription for the vinegar is clear (as opposed to blackeyedgurl's "diluted"), and has been tested (by me) on catnip. (Note: "Vinegar" means the 5% vinegar that's what one gets at a store.) It's always the case that one may want to try even more-dilute mixtures first, especially on fragile or valuable plants. And concerning your "carelessly watered in": To be clear, I wasn't talking about "watering in", just spraying the foliage (although some say that lightly spraying the surface of the soil can help with fungus gnats). Of course, when one sprays the foliage, there's always the issue of how much ends up in the soil. Optimally, none would - and I work to achieve that as much as possible - but lotsa times, that's unavoidable to some extent. Note that this vinegar solution is so dilute that application such as the above shouldn't change the pH of any soil-based medium, absent extreme over-administration. . "I always cringe a little when someone recommends pure soap or real soap, but don't explain what that means. I suggest that anyone discussing a 'pure soap' be prepared to give examples, brand names. I assume that you mean a plant based liquid soap, free from fragrances and dyes?" So do I - especially since I killed two camellias by using dish-washing liquid that must've had some extra ingredients (duh! talk about careless! I should've tried it on a small part of the plants first.)). Since then, I've used Dr. Bronner's Pure Castile liquid, without any problem. I'm confident that other Castile soaps - either liquid or solid - would be just fine - as would Ivory, no doubt. . "My favorite home remedy for PM is 1 T. baking soda, 1 tsp. horticultural oil, 1 tsp. insecticidal soap, and 1 gallon of water." I've not used oil, since it seems that (and sounds like) it would introduce unnecessary problems. Relatedly, several sources I found said that Baking Soda is ineffective without horticultural oil!
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Ejperryman, that's what the article below appears to confirm - you will see improvement with new growth. With most plants, new growth can occur through the entire growing season (approximately March - October). Here is a link that might be useful: Dogwood Powdery Mildew
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Hi Kimmsr. I started with the apple cider vinegar solution after seeing it here on gardenweb, mainly because I happened to have a quart bottle of it! My PM problem is not extensive--only four to five shrubs affected and only one of these with PM on every leaf. My Mm Isaac Pereire gets curled leaves and puny blooms. The vinegar solution definately arrests the progress--the day after a spray it is pretty much gone. My guess is that the specific ph that PM needs can be altered either way--with an acid or a base. Now I'm trying the Cornell Formula on some roses and the vinegar solution on others (trying to find roses equally affected). I'm getting obsessed! A question: Does it completely nullify your efforts when you spray in the evening and it rains the next day?
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IME, different cultivars of nandina have different susceptibility to powdery mildew. I have found Firepower extremely prone (also to various leaf spots), also Plum Passion and other newer intros with purple foliage coloring. And the straight species. Gulf Stream and Sienna Sunrise are quite resistant in my experience.......I have grown both for years and use them extensively in my designs with NO issues. Gulf Stream appears to be what kathi is showing in her photos. You might want to read THIS publication (an exerpt from the PNW disease management handbook) as it lists both some cultural controls that can limit the disease development to begin with as well as a recommendation of various commercial fungicides that can be used preventatively. Nearly all fungicides available to homeowners will be preventative rather than curative so you need to start applications before you see any symptoms of the disease.
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mike_rivers
16 years ago
The Rosemania site also recommends Systhane for powdery mildew. Systhane is myclobutanil which is available cheaply at Home Depot-type stores as Immunox.
diane_nj 6b/7a
16 years ago
Immunox. I mix it in with by usual combination during PM season.
shelby_nj
16 years ago
I just applied now Fungicide from Garden Safe. On the ingredient list it says clarified hydrophobic extract of neem oil.I wonder how that product is. My roses have not yet shown any signs of infection. They look healthy. But just as a cautionary step I applied. Is there any fungicide that we can directly apply to the soil rather than spray for roses to avoid black spots?
jerijen
16 years ago
Applying chemicals to the soil is an expensive and inefficient way to treat the foliage.

Jeri
zack_lau z6 CT ARS Consulting Rosarian
16 years ago
I use Immunox. Immunox plus has an insecticide that I don't need. In our area Home Depot has one type and Lowes has the other.
ceterum
Original Author
16 years ago
Thank you, I get Immunox. We may even have it from times before Banner Maxx, Mancozeb and Tebuconazole but I would not dare to use a product that is 4-5 years old.

Decobug, I have about 300 roses and only 3 were suspectible to PM so far. None of the rest have ever had PM and some roses are with me for 8 years or more.
hoovb zone 9 sunset 23
16 years ago
I used E-Rase, I think it is called. As far as I can remember it is basically neem oil. It worked surprisingly well. I don't get much PM, so the bottle is still almost full.
williamcartwright
16 years ago
I find washing the foliage well with water using low pressure is a pretty effective way to knock down PM, especially if done at the very first sign.

And even gently rubbing areas were you can see "spores" on leaves while gently running water over them, seems to flush the PM off the leaves. Takes a little work, but I've had very good success with this method.

Bill
jerijen
16 years ago
E-Rase is soy oil, I think.
Same-same, in effect.

DO NOT use it if the weather's going up over 80 degrees. You'll fry the leaves.
(How do I know this? Learned the hard way, of course.)

It smothers the spores.
Bill's right, too, rubbing and washing is effective.

And, FWIW, if a rose continues to mildew here, it just -- doesn't stay around long.
Life's too short to struggle with roses un-suited to my conditions.

Jeri
diggerdave
16 years ago
Thanks Bill :) Back when powdery mildew was a problem here, I would rub the worst leaves and it removed the pm. The leaves stayed distorted but the powder was gone. I thought I was the only one crazy enough to do that and think it helped.
I quit using fungicide 4 years ago and wash foliage with a hard, fine water spray. The only powdery mildew seen since was when I quit washing certain roses to see if they would get it and their neighbors didn't. I quit doing that once my experiments showed me washing foliage was the key. Now I'm going to have to experiment with low pressure washing.... why did I read this? LOL

Powdery mildew - most effective fungicide?

Comments (12)

Jean Marion (z6a Idaho)

hartwood

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zack_lau z6 CT ARS Consulting Rosarian

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hoovb zone 9 sunset 23

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jerijen

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Powdery mildew - most effective fungicide?

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