How to Use Milk to Control Powdery Mildew

Powdery mildew on rose foliage
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Does Milk Control Powdery Mildew?

You can do everything right in your garden and there will still be problems - like powdery mildew. Some things are beyond our control. When weather conditions are right, a host of fungal diseases will move in. Keeping your plants healthy and giving them plenty of air circulation will help them withstand many problems, but not all. Sometimes you need the help of a fungicide.

However, that does not necessarily mean you need to use chemicals.

What is Powdery Mildew?

Powdery mildew refers to a group of diseases that all show up as a powdery white coating on leaves, stems, and sometimes even flowers. It does not usually kill plants, but it can weaken them and diminish photosynthesis, leading to poor yield and plants that don't last the season.

It is spread by spores that are carried by the wind or splashed onto leaves. Powdery mildew favors humid, rather than wet conditions. The spores form when the humidity is high and disperse when the humidity diminishes. Spores can over-winter on plants or plant debris and start the process all over again. End of season garden clean-up and planting disease resistant varieties are your best powdery mildew controls.

Although powdery mildew affects many plants, there are several species of powdery mildew fungus and they each have their preferred hosts.

So powdery mildew on zinnias will not move to lilacs or cucumbers.

No matter what plant has powdery mildew, this is a fast spreading problem and you need to take action quickly. However you don't need to reach for the big guns. There are a handful of relatively low toxic remedies and most can be homemade.

A baking soda solution is one and the following milk solution is another.

Using Milk as a Fungicide

Milk has become the latest secret weapon in fighting powdery mildew. Actually it's not so secret and it's been used in treating diseases for decades. It's been tried as an additive to improve the spreading and sticking of other pesticides and Dr. Linda Chalker-Scott, of Washington State University, cites many studies where milk was tested against the transmission of tobacco mosaic and other viruses. - to mixed reviews.

Most recently, milk has been getting a lot of good press as an anti-fungal spray, specifically against powdery mildew on cucumbers and squash.

How to Use Milk to Control Powdery Mildew

The dilution used by home gardeners is:

  • 1 part milk to 2 - 3 parts water.

The solution is then sprayed on the plant's leaves every 10-14 days. It works best as a preventative, rather than a cure, which makes it hard to determine whether it actually works since you don't know if your plants would have gotten it anyway.

How does Milk Work as a Fungicide?

For the past several years, researchers have been experimenting with spraying a diluted solution of regular milk on a variety of plants, mostly cucurbits (squash and cucumbers).

They have been seeing enough success to continue experimenting. Home gardeners are now getting in on the research, but very often a control group is missing, so their results are not definitive.

As to exactly how milk works against the fungus, no one is certain. It appears that the proteins in milk offer an antiseptic-like effect, when exposed to sunlight. To be effective, the solution should be applied in bright sun. Soak both sides of the leaves until the solution is dripping.

If you've ever left milk out in heat or direct sun, you know that the odor of spoiled milk is not pleasant, but it does dissipate somewhat quickly. The protein is in the milk fat, and both whole and skim milk have been tried by home gardeners. In fact, researchers used whey, a milk by-product, because it was cheaper.

You can try your own experiments with whatever you have on hand. To really test it, spray the solution on only some plants and leave others untreated.

Author and horticulture professor Dr. Jeff Gillman has also recommended using the milk solution for black spot on roses. There hasn't been a lot of institutional research on this, but home remedies are not profitable and often get short shrift in research. Interestingly, Dr. Gillman also recommends simply spraying plants prone to mildew with water. Since powdery mildew doesn't like getting wet, spraying the plants daily seems to help thwart it.