Magic Milk for Powdery Mildew

White lilac with powdery mildew - not sprayed_edited You know … the unattractive white powdery-looking spots that seem to appear from nowhere during mid- to late-summer?  These fungal spots begin on lower leaves and can quickly spread to cover leaf surfaces of entire plants.  Lilacs, phlox, bee balm, asters, dahlias, cucumber and summer squash are all susceptible, particularly if the plants do not have good air circulation (a problem I plant to avoid).  Not liking to spray fungicides, I’ve tolerated powdery mildew for years.  But when cleaning up paperwork this past winter, I found a note I had jotted down, likely while watching any one of gardening shows I try to take in during cold weather months.  The note said: powdery mildew; 1 part milk to 9 parts water; spray 2x weekly.

My guess is this tidbit of advice came from one of those shows HGTV deemed unworthy … probably Gardening by the Yard … but I can’t be sure.  It also may have come from an old Victory Garden show on PBS.  Anyway, I tried this concoction on all my phlox, one lilac (saving the others for comparison), and my cucumbers and summer squash.  In previous years all had been covered by powdery mildew.  The cucumbers and squash would simply succumb. The phlox would valiantly bloom on in spite of the truly unattractive appearance of its leaves. The photo at the top shows an unsprayed lilac … it just looks plain sad.   The photos below show a nearby lilac two weeks after just one magic milk spray.  The powdery mildew is not completely gone – you can see a few traces on the lower leaves – but is controlled.  Just one spraying of magic milk stopped powdery mildew in its fuzzy little tracks on my cucumbers and squash  leaves – though I will spray again for insurance.  The phlox leaves look better than they ever have by this time of year … two weeks after the initial spray only small traces of powdery mildew appeared – I re-sprayed.  

white lilac milk-sprayed for powdery mildew_editedwhite lilac previously milk-sprayed for powdery mildew_edited

I’ve not yet figured out exactly why milk works to stem the spread of powdery mildew – there must be a substance in milk that holds fungus in check – but I’d love to hear from anyone who can explain milk’s effect.  But the point is it works, it requires no special permit to use, and its nearly free.

7 comments for “Magic Milk for Powdery Mildew

  1. August 26, 2009 at 7:06 am

    Joene,

    Wow! I didn’t realize there was a way to ‘reverse’ powdery mildew. I’m going to have to try the magic milk in my garden on a few plants even though this year powdery mildew does not seem to be too serious of an issue here. Of course, I have lots of other fungus issues so I think I’ll experiment with the magic milk and see if it works on other fungal diseases too.

  2. joenesgarden
    August 26, 2009 at 7:42 am

    Debbie: Rather than totally ‘reverse’ powdery mildew, the milk spray seems to curb its spread and minimize the look of the white blotches. I seem to recall reading that milk works similarly on black spot. Do let me know how your experiments go … it’s so nice to have such an easy, low-cost intervention work so well.

    Your section of our state has received more rain in August … when you had T-storms we had nada. But the humidity has been high for the entire month – perfect for powdery mildew.

  3. Stacy
    September 11, 2009 at 11:13 pm

    I have just started treating my summer squash this way and hope to have the results you’ve had. They did seem better in just 24 hours, but that might be wishful thinking. It has been so humid here in Oregon over the past 3 weeks that the fungus was taking over and nearly killing my plants . . . thank you for sharing your experience with it!

  4. A
    September 13, 2009 at 9:45 pm

    Milk solution does indeed seem helpful, although don’t be tempted to increase the percentages, apparently anything over ~20% will result in your plants smelling of rancid milk… Lower fat milks are less likely to clog your sprayer.

    From reading around on this, I’ve heard it suggested that it’s the enzymes within milk that help here. Not sure which ones, or exactly how though. Another article suggests it’s a pH thing, the milk makes the surface of the leaves more alkaline, which apparently doesn’t suit mildew.

    You may also find a weak solution of bicarb (baking soda/bicarbonate of soda) helps – I use 5 tsp bicarb per gallon of water.

    I’ve tried mixing the two ideas, and it does still seem to help, but I’m not sure whether mixing them helps more than each individual treatment does; or whether mixing with bicarb simply invalidates the milk.

  5. joenesgarden
    September 15, 2009 at 11:17 pm

    Stacy: good luck keeping your powdery mildew in check. I think results are better when outbreaks are treated early.

    A: thanks for the additional info. I’ve meant to try the baking soda spray but have not done so yet. Does the baking soda leave any residue on leaves?

    Glad you both stopped by and took the time to comment.

  6. A
    September 19, 2009 at 9:39 pm

    It’s hard to say whether there’s much residue, I’m spraying outdoors on mildewy leaves, and it always seems to be raining ;)

    That said I think the pH theory is probably a red herring, as milk is around pH6.7 which is close to neutral. Since it’s only a 10% solution anyway, I think the pH on the leaf surfaces won’t change much when sprayed with it.

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