This is one fast growing crop that I didn’t intend to grow. I think I “bought” this problem of powdery mildew when I did a foliar spray with some fish emulsion that was then followed by multiple damp dark gloomy depressing sunless days.
Within a week, it has really done a number on my vine crops.
It doesn’t really upset me because this represents a teachable moment. My family will not starve due to a reduced number of spaghetti squash and mini-pumpkins and I will, hopefully, learn something about how to cope with powdery mildew.
Lesson #1: Once it starts, its not going away so you have to “deal” with it if you do not want it to spread everywhere.
Lesson #2: It might start in the shade but it will be happy spreading to sunny locations.
While searching for an organic way of dealing with this problem I came across this paper by Crisp, Wicks, Troup, and Scott called “Mode of action of milk and whey of in the control of grapevine powdery mildew” (PDF format) in the journal called Australasian Plant Pathology, published in 2006 (Australasian Plant Pathology, 2006, 35, 487–493).
Powdery mildew takes out all sorts of crops and can be especially vicious to wine grapes. Control of powdery mildew in wine grapes has been done by spraying with sulfur containing fungicides. This is why wines are contaminated with sulfites (and why I can not drink wine, I am violently allergic to these sulfites).
Its been known for some years that spraying a 10% skim milk or whey solution on affected plants is very effective in the treatment of powdery mildew.
This paper reports that sunlight interacts with the milk to form oxygen free radicals that collapse the hyphae of the organism grapevine Erysiphe (Uncinula) necator which we call powdery mildew (zucchini is effected by Sphaerotheca fuliginea). It also damages the conidia (asexual, non-motile spores of a fungus) within 24 hours of treatment.
Some people use hydrogen peroxide, a rich source of oxygen free radicals, but this paper reports that H2O2 doesn’t do anything to the conidia and that it encourages germination of this fungus.
Interesting huh?
Must be that the free radicals produced by photo-oxidation of something in the milk acts by a different mechanism than the free radicals in hydrogen peroxide. Or does it?!
The answer lies in complexity. Read on.
When they looked at a specific component of milk called lactoferrin (a globular multifunctional protein with antimicrobial activity (bacteriocide, fungicide – WIKI, an 80 kDa iron-binding glycoprotein, binds to the membranes of various bacteria and fungi, causing damage to membranes and loss of cytoplasmic fluids – paper), a part of the innate defense, conidia were ruptured but hyphae were not effected until 48 hours out.
This indicates, as per these authors and seems intuitive, that milk has a bipartite action against powdery mildew:
- photo-induced free radical activity
- lactoferrin mediated rupture of conidia
The authors close by saying that the mechanism by which lactoferrin is effecting the conidia is not clear. They also think that there many be other parts of milk which could be having an anti-mildew effect.
I will be spraying my unfortunate mildew-infested plants with a 10% skim milk solution (shown below) and I will let you know how it goes!
Drop me a comment if you have had success with this method.
Measure a 1:10 milk:water solution into a sprayer. I am using skim now but I might try a whole fat to see if there might be some fat-soluble or fatty acid aspects. I might even use raw if all else fails!
If I were being scientific about this, I would leave a section unssprayed, spray one section each of – skim, whole commercial, whole raw. This is not scientific, its going to be anecdotal and descriptive and with no controls because I started out just desperate to attack the problem so I do not have any untreated plants right now.
As I am not a mycological physiologist and I am not working of a government grant, I think its going to be ok.
Pour in the milk.
Pour in the water, mix it all up in a bucket.
Spray on a SUNNY DAY, not cloudy.
Watch.
Spray twice a week.
Watch.
Blog.
Lets hope I can see SOME result otherwise there will be no follow up to this post and you will be left hanging!
Hi Nika,
You asked if anyone has had success with this method, so I thought I would comment. I used the 10% milk solution spray to combat powdery mildew on my squash plants this year with about 90-95% success. I was really happy to see it worked pretty well! It did leave a bit of a sour milk smell (I used 2% milk because that is what I had on hand) but it only lingered a day or two. I’ve read that the higher the fat content, the more odor you get. The faint smell we had was certainly worth the results! I used it on zucchini, patty pan squash, and crookneck squash. Later on I did get some mildew on my butternut squash, but it did not take hold and spread throughout all the plants, so I never sprayed them. It seems butternut squash is resistent to powdery mildew.
Don’t leave us hanging! Let us know how it worked for you!
Ingrid: I am so happy it worked for you! That helps me feel better about this method.
The jury is still out here on whether it is working.
Now, on top of this problem, we are dealing with a drought, after TOO Much rain for weeks on end. For this reason, these poor plants are now stressed out at least two different ways!
Wow Nika, what a gorgeous blog you have here! My garden has been such a disaster this year, but I’m trying to write down as much as possible so that it is a learning experience, and I just keep telling myself that. It sounds like you and your family are doing exactly what we hope to do in another year or two- with the vegetable gardens, chickens, etc. I will be keeping an eye out here that’s for sure.
Erika: Sorry to hear that you garden didn’t do what you wanted it to do. Was it from lack of rain or too much? I cant recommend raised beds enough because it seems like you can get so much more productivity out of them (and bugs and rodents were not a huge issue – as long as you go organic the system takes care of itself for the most part)..
I wish you all the luck and please stay in touch!
Ah, well, my problem turned out to be ground squirrels. I have partially raised beds- but no barrier underneath, which obviously needs to be fixed for next year. When I finally ripped out my yellowed and non-producing melons and cucumbers I found literally dozens of holes. The squirrels were feasting on my roots.
I also need to do more soil ammending and more careful timing. I was so eager to get everything in this past spring, that it didn’t occur to me that my broccoli should wait a while so it wasn’t about to head at the peak of summer heat- that was some bitter broccoli.
Your gardens are simply stunning. I’ve read all your posts and am watching with some serious garden envy.
I’ll bet your homeschoolers are getting a fantastic opportunity for hands-on learning.
Yeah, one year our garden was eaten out from underneath by voracious chipmunks. This is why we put down the wire mesh. Indeed my oldest homeschooler has helped a lot! This coming year I am going to involve her much more in the planning, planting, weeding, etc!
hi, I have the mildew in all my squashes and it is very advaced. I will try milk to see. I wonder if is it efficiente because all the chemicals antifungi stuff in the milk or if I use organic milk will still work… i’ll see. thanks!
atrix: The part of the milk that does the magic here isnt chemicals that are added to it, its a natural part of the milk so organic or conventional is the same.
Hi, my pumpkins have been attacked by powdery mildew this year. I’ve been spraying a milk solution once a week for 3weeks. But I’m not getting much of a result. Any secrets?
Erin,
The problem with powdery mildew and any treatment for it is that you have to start the moment you see the slightest sign of it. If its more advanced, even the most aggressive chemicals cant do much.
Also, this treatment requires sunshine to do the photooxidation of the milk chemicals. Powdery mildew comes when plants are too crowed, too wet (too much leaf watering? dont water leaves at all, water UNDER leaves) and when its been dank with poor sunshine. In the final case, its hard for the sun to do its thing if the sun is hidden! (Like around here almost all spring it seems).
Last summer I planted my mildew prone plants all by themselves, they got lots of sun, etc, but they still got mildew BUT I trimmed off the bad bits and was still able to get some production from them.
Try to buy mildew resistant varieties, that may be the best solution.
Thanks Nika, I realised my pumpkins were getting a lot of shade because I have put shadecloth over my garden as I’m in Australia and it gets very hot! So I’ve pulled it down and trimmed off all the affected leaves. Now I’ll just keep my fingers crossed!
Thanks for all your help!
Erin,
Ohh, that is good news – lets hope that makes all the difference!
Hi…
I Don’t know if you can help me, but my Bankshire Rose is covered in an advanced stage of powdery mildew, is it even worth trying to safe it, I have used the store bought stuff, and I was thinking of trying milk… but to be honest the poor things leaves just get covered… Any advice?
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Great Blog. I stumbled here as I was searching for information on using whey to combat powdery mildew… pleasantly surprised to see you’re near where I grew up (Dudley). I’m a Navy wife now living in VA. Zone 8 rocks, not sure I’ll ever be able to go back ‘home’ to settle down because gardening is so much easier here
Thanks for the idea. I have the same problem with squash and zucchini. I’ll give it a go!
[…] going to have to try a water spay made of 1:10 milk solution. We’ll have to wait for the “June Gloom” to dissipate as you need a sunny […]
Thought I should add that sulfites in wine generally come from two sources. One is the metabisulfites added as a wine stabilizer. This is the added sulfite in most wines. Howevr, there are sulfites in all wines because it is produced by the yeast during fermentation. It is unlikely that sprayed sulfur would form sulfites in the grapes.
[…] ask me how it works. All I know is that it does. I’ve heard that some studies have shown milk to be as effective against powdery mildew as […]