Best Treatment for Powdery Mildew?

mike_in_new_orleans(9a/ coastal LA)August 7, 2010

OK, this seems like a basic question, but I don't get much PM in my area, usually just a lot of blackspot. But its been fairly dry lately and very warm with warm nights, humid but not raining. I'm starting to see some PM starting on a few bushes. What are your preferences for treating it? I use Bayer Advanced Disease Control for blackspot but I don't think it eradicates the mildew very well. What about baking soda and water? Any good? If so, what consentration level? What about commercial sprays? What are the best?

Thanks! Mike

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buford(7 NE GA)

I had some on my double delight. It looked like it was actually deforming the buds. But I had been spraying with Bayer. I thought about spraying with Daconil, but I never got around to it. It's still there, but the blooms opened and looked fine. I'm thinking of just ignoring it:) Like you it's been very hot and humid here for weeks with little relief in sight. We get rain, but apparently not enough to take care of the PM.

    Bookmark   August 7, 2010 at 7:01PM
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Maryl zone 7a

I battled PM for years when I first began growing roses. I remember someone saying that there seemed to be a correlation between fragrant roses and susceptibility to PM. In my case at least, that was a pretty valid relationship as I started out growing only fragrant roses. Anyway, because of this I became pretty familiar with sprays for Powdery Mildew and the best for prevention of normal outbreaks IMO was Ortho's Fungunex with Triforene (Ortho's Rose Pride now). I still use it in the spring here. For severe outbreaks I used Rubigan (it's not effective against BS however). I did try a baking soda recipe off this forum when there were a bazillon of them first floating around, and it was bad - defoliation on some roses and burn on others. Later I tried a commercial formulation of the above called Remedy. It actually seemed to work - at least it did no harm. BUT, I still had to spray again against BS as baking soda is ineffectual on that fungus. The upshot is since I hate spraying I just stuck with Fungunex and tried to keep up on the cultural aids (well watered roses, plenty of air circulation etc). I don't know about the Bayer products vs Triforene in Orthos. I haven't bothered to use them for PM because I am perfectly satisfied with Ortho. My motto is if it ain't broke don't fix it.

    Bookmark   August 7, 2010 at 7:08PM
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chefcdp(z4a MN)

I have found that around here, Tropical Minnesota -zone 4a, the Bayer Advanced Disease Control spray does the best job.

It allowed me to grow PM magnets such as Folksinger and Champlain PM free after years of trying other sprays including some that were highly touted for PM.

There are different strains of PM so your mileage may vary.


    Bookmark   August 7, 2010 at 7:56PM
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kstrong(10 So Cal)

Powdery Mildew is the disease of choice here in mildew heaven -- a coastal foggy canyon two miles from the ocean. The best fungicide, hands down, is Compass. Next is Rubigan. Both of those will deal with severe mildew well, and prevent new outbreaks. Banner Maxx is useless here.

But I have a different idea for you, which may also work given that you say your outbreak isn't too, too bad -- Canola Oil. You need to use the emulsified kind, the best of which is branded Natria Multi Insect Control (by Bayer). This product is 96% emulsified Canola Oil. There is another one by Lilly Miller called Veg-Ol, but it burned my foliage whereas the Natria brand did not. The application rate that works for mildew is 4 Tablespoons per gallon. Try that first.


    Bookmark   August 7, 2010 at 8:13PM
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jerijen(Zone 10)

Kathy's suggestion is a good one.

None of the chemical fungicides will ERADICATE mildew, once it is present.

An oil spray, such as she suggests, will smother the mildew, and sort of hide it.


    Bookmark   August 7, 2010 at 8:39PM
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diane_nj 6b/7a

The best commercial fungicide for me had been Immunox (w/o insecticide, hard to find these days).

For something "natural", you could also try milk (1 part milk/9 parts water). I'm skittish about any oils, but that's just me.

    Bookmark   August 7, 2010 at 9:29PM
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kstrong(10 So Cal)

By the way, buford, you should continue to forget to use the Daconil on Double Delight. The two of them DO NOT get along. For some reason, that particular cultivar, Double Delight, is susceptible to lots of foliar damage and discoloration from Daconil. I don't know why, but someone told me that and I tried it on one cane, and it's true. I use Daconil sometimes in my rotation (only when temps are cool), but I skip the Double Delight plant on those sprayings. I know that sounds peculiar, but so it is.


    Bookmark   August 7, 2010 at 9:57PM
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jerijen(Zone 10)

To be completely honest, my "cure" for powdery mildew is a shovel.
I don't mind a little touch of it under extreme conditions, but it is a rare rose indeed that will remain here if it mildews regularly.

It's far easier, and far more sensible in the long run, to dig it up, toss it, and plant something that doesn't need all that spray and work.

I apply the same "treatment" to roses that rust.


    Bookmark   August 7, 2010 at 11:06PM
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kstrong(10 So Cal)

Even Grandmother's Hat mildews here, Jeri. Nearly everything does.

    Bookmark   August 7, 2010 at 11:27PM
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mike_in_new_orleans(9a/ coastal LA)

Thanks folks. I'll have to rummage and see if I still have a bottle of Ortho with triforine in it. Of course I have a bottle of the useless Banner Max but none of the suggested Compass or Rubigan Kathy mentioned. I get anxious considering oils, because I have badly chemical-burned roses in the past trying to use Greelgiht Neem Oil concoction. It was horrible! Must be our summer heat. I don't know.

    Bookmark   August 8, 2010 at 1:22AM
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buford(7 NE GA)

Katy, I used to use Daconil every week and didn't have a problem with it. But I was very careful to do it early in the AM and when the roses were hydrated. In fact, my DD didn't really do well until I sprayed it regularly (it would get bs so bad it never really bloomed).

This year is so strange. Some roses I normally get mild PM on (Sophie's Rose) have none, but what I have on DD is weird. Very thick grey and keeping the buds closed. I did try just wiping it off. It's strange that just this one plant has it. But like I said, it seems to be blooming ok so I'm just going to leave it. And pray fall comes sooner rather than later.

    Bookmark   August 8, 2010 at 8:04AM
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jerijen(Zone 10)

Kathy -- How old is your Grandmother's Hat?

Have you grown, umm ... Bishop Darlington?
Fourth of July?
Rosette Delizy?


    Bookmark   August 8, 2010 at 4:11PM
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kstrong(10 So Cal)

I got Grandmother's Hat in Aug '07, so 3 years. And I do have 4th of July, actually 4 of them, and it does not mildew, but it does rust once in awhile in the season. I don't have the others on your list. That said, I exaggerated a little when I said everything mildews here. I recently made a list for publication on the rose society site of roses that don't mildew here, and those were the following roses.

Hybrid Tea/Grandifloras:
Cherry Parfait (red/white)
Frivolous Pink (pink/yellow)
Lasting Love (red)
Honey Dijon (gold)
Stephen Rulo (lavender/brown)
. . .
Julia Child (yellow)
Shockwave (brightest yellow)
White Licorice (light yellow)
Lovestruck (pink speckled)
Playboy (orange/yellow)
Gebruder Grimm (brightest orange)
Kimberlina (pink)
Perfume Tiger (yellow/pink stripe)
Hot Cocoa (russet)
. . .
Darlow's Enigma (white fragrant hybrid musk)
Dragon's Blood (dark red big shrub)
Red Ribbons (red groundcover)
My Stars (thornless dark pink)
Rural England (reblooming pink rambler)
Route 66 (purple)
Mme. Plantier (white once blooming alba)
. . .
Berries n Cream (pink/white stripe)
Candy Land (pink/yellow stripe)
Fourth of July (red/white stripe)
Rhapsody in Blue (it's a climber for me -- purple)
Blaze of Glory (brightest orange/red)
. . .
Irene Marie (yellow with red picotee)
Swedish Doll (orange/red)
Sequoia Twist (orange/yellow stripe)
Gourmet Popcorn (white polyantha-like shrub)
Gingerbread Man (dark yellow)
Gizmo (orange single)
Hurdy Gurdy (red/white striped mini climber)
. . .
Everything else gets sprayed fairly consistently all year.


    Bookmark   August 8, 2010 at 4:34PM
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jim1961 Zone 6a Central Pa.


You don't have botrytis blight on DD do you?

Here is a link that might be useful: botrytis blight

    Bookmark   August 8, 2010 at 9:44PM
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Mike, one more suggestion: make sure your roses are getting enough water. Stressed roses are more susceptible to fungal complaints.

    Bookmark   August 8, 2010 at 9:45PM
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Regularly spray your roses, both leaves and canes, *hard* with water coming out at full tilt from the hose. (Don't do it when the sun is shining directly on them.) Do it every day until you see that the mildew gone, and then don't wait too many days before repeating the treatment if you don't have any hard rains.

Best wishes,

    Bookmark   August 9, 2010 at 12:55AM
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mike_in_new_orleans(9a/ coastal LA)

Berndoodle, thanks for the tip. I'm watering them every day right now.


    Bookmark   August 9, 2010 at 3:57AM
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buford(7 NE GA)

jim, that does sound like what I had. I thought boytritis was a cooler weather disease that made pink spots on white petals. I did have a bunch of that this spring.

Thanks for the info.

    Bookmark   August 9, 2010 at 6:16AM
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