Photo courtesy of alisdair at Flickr.com.
If the milk in your fridge is fast approaching its use-by date, don’t just throw it away—use it in your garden! A strong milk solution can be just as effective at controlling powdery mildew as some chemical fungicides, killing up to 90% of the disease on contact. It’s cheaper than chemicals, too. The most effective concentration is about 10%, or one part milk to nine parts water. The weaker the solution, however, the more often you have to spray to keep the microbes away; for example, you’ll need to spray every four days or so with the 10% solution.
Using milk is a lot neater than the other popular organic method for controlling powdery mildew, which involves mixing baking soda with a sticky surfactant like insecticidal soap or horticultural oil. Not only is the baking soda recipe messy, it can burn your plants if you over-apply it, and it’s not recommended for use in full sun. These aren’t things you have to worry about with “milkicide,” but do keep this in mind: concentrations in excess of 30% can attract other fungi. Those fungi won’t hurt your plants, but they won’t help them either.
In addition to knocking out powdery mildew, milk also does a number on botrytis (a.k.a., gray mold) and black spot disease, the bane of rose growers everywhere. While it won’t make existing infections of the latter go away, it will keep them from spreading; and if you use it as a preventative, it will keep them from appearing in the first place.
You can load the milk solution directly into your sprayer and use it as a foliar spray. In addition to being a natural germicide, milk also contains naturally-occurring nutrients like carbohydrates, proteins, amino acids and organic salts. If you use skim milk, you don’t need to worry much about odor.
Don’t do dairy? Check out this organic fungicide for powdery mildew.