this late in flower the best solution is milk which has already been suggested.
...i know this works because i used it the one time i had pm, also brought to me via a gifted clone.
first, you can use ANY kind of milk, even powdered milk will work and all you do is mix it up as strong as you want, it's safe to spray on the plants straight but milk is thick and it WILL clog your sprayers if you don't dilute it, ...i dilute it at 10 parts water to 1 part milk, then you just spray the crap out of your plants, paying particular attention to the leaves, and don't forget to spray the undersides, and all your vegging plants too, pm is a kind of fungi and spreads by spore and the spores are ubiquitous so if the conditions are right, anyone can get pm and if you already have it anywhere in your garden, you have it EVERYWHERE in your garden.
...also, go easier on spraying the buds, especially as you get further into flower because too much moisture in the buds can cause mold.
...in my own case i sprayed the milk solution every few days for about a month before the pm stopped coming back and that's because pm is like an infection and so is systemic and you either use harsh chemicals, which of course you can't while in flower, or you use milk. (sulfur burners are also effective as a preventative but they aren't really applicable in a small grow)
bozo
btw, here is some info i found on milk when i was dealing with my own pm problem that may help you understand the research and why it works, ...you'll see that milk actually boosts your plants immune system.
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Milk is a useful fungicide in the garden, and is more effective than standard chemical brands.
Researchers believe the potassium phosphate in milk boosts a plant's immune system to fight the fungi.
Where most organic gardeners use a baking soda, soap and oil solution, milk may be substituted to combat the unwanted fungus.
Preparing a Milk Solution and Spraying Schedule
The correct dilution and spraying schedule for garden plants depends on the situation and takes some trial and error.
A milk fungicide solution can range from 1 part milk to 9 parts water, to a strong, milk-only solution. A 1:1 dilution may work for a week, but a 1:8 solution requires spraying every 3 or 4 days.
Skim milk may work better than whole milk, as the higher fat milk may clog a sprayer; even reconstituted powdered milk works.
Uses for Milk Fungicide
Milk was originally used in the garden to treat powdery mildew on squash plants. It is now also commonly used on flowers such as rudebekia (Black-eyed Susans) and Begonias to cure powdery mildew.
Milk has also been used to cure Botrytis on a Cyclamen houseplant. This was applied full strength every morning (leftover breakfast milk). Rotten leaves were picked away and the plant pulled through with no more Botrytis.
Black spots and rust on roses can be controlled but not cured with milk. Fortunately, milk can prevent the spread of these fungi to other plants and new leaves. This can be very useful when bringing home a plant from the nursery and finding a black spot.
The copyright of the article Milk as a Garden Fungicide for Powdery Mildew, Botrytis, and Black Spots in Organic Gardening is owned by Deborah Turton. Permission to republish Milk as a Garden Fungicide for Powdery Mildew, Botrytis, and Black Spots in print or online must be granted by the author in writing.
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by Arzeena Hamir
Powdery Mildew
Less than 3 years ago, researchers in South America discovered a new alternative to controlling powdery mildew. Wagner Bettiol, a scientist from Brazil, found that weekly sprays of milk controlled powdery mildew in zucchini just as effectively as synthetic fungicides such as fenarimol or benomyl. Not only was milk found to be effective at controlling the disease, it also acted as a foliar fertilizer, boosting the plant's immune system.
Powdery mildew in the cucurbit family is caused by the organism Sphaerotheca Fuliginea. It is a serious disease that occurs worldwide. For decades, organic gardeners had to rely on making a spray from baking soda to control the disease. Now, instead of measuring out the baking soda and combining it with a surfactant (a "sticking" substance) of either oil or soap, gardeners need only head for their refrigerators.
In his experiments with zucchini plants, Bettiol found that a weekly spray of milk at a concentration of at least 10% (1 part milk to 9 parts water) significantly reduced the severity of powdery mildew infection on the plants by 90%. While some gardeners may be tempted to increase the concentration of milk for more control, Bettiol found that once concentrations rose above 30%, an innoccuous fungus began to grow on the plants. How does milk control powdery mildew?
Scientist aren't 100% sure how milk works to control this disease. It seems that milk is a natural germicide. In addition, it contains several naturally occurring salts and amino acids that are taken up by the plant. From previous experiments using sodium bicarbonate, potassium phosphate, and other salts, researchers have found that the disease is sensitive to these salts. It is possible then, that milk boosts the plant's immune system to prevent the disease.
Milk used around the world
The benefits of using milk to control powdery mildew haven't been isolated to Brazil. Melon growers in New Zealand are saving thousands of dollars every year by spraying their crops with milk instead of synthetic fungicides. The melon growers in New Zealand have been so successful that the wine industry is taking notice and beginning experiments using milk to control powdery mildew in grapes.
What kind of milk should be used?
In Bettiol's original experiment, fresh milk was used, straight from the cow. However, this is obviously not feasible to most home gardeners. The research work in New Zealand actually found that using skim milk was just as effective. Not only was it cheaper, but the fact that the milk had no fat content meant that there was less chance of any odours.
Wagner Bettiol's original article was published in the journal Crop Science (Vol. 18, 1999, pp. 489-92).
