How To Treat Powdery Mildew In Your Small Space Garden

Milk spray! Yes milk is what I use on the Balcony to control the dreaded white scourge!

Summer wouldn't be the same without powdery mildew in the garden! The Balcony garden is not immune to bouts of this dreaded growth, this Summer is no exception and seems to be even harsher due to copious rain fall over recent months.

I've sifted through all the research on the subject for you and distilled it into this easy guide so that you too can manage and treat this very common plant malady - so do not consider yourself a failure if your plants are covered in this scourge, it is all part of the Summer growing experience!

What Does Powdery Mildew Look Like?

It is whitish/grey patches on the leaves that starts as a few white spots and then very quickly spreads to a fuzzy coating when the conditions are right, commonly on roses, Rosemary, grapes, crepe myrtles, dahlias, zinnias, calendulas, sweet peas, cucurbits and vine crops appears when humidity is high. It is fast growing!

What Is Powdery Mildew?

Powdery mildew fungi are present in many environments.  But when the right strain of powdery mildew finds a suitable host plant, it quickly sinks root-like structures into the cells on the leaf's surface. There it stays, taking nutrition from the leaf while developing a matrix of thread-like structures over the surface. This is when we gardeners notice unusual patches of white or light grey with a powdery or furry texture, usually on the top sides of leaves. It cripples its ability to photosynthesise by blocking out light, and inhibits the leaf's gas exchange system, too. 

What Conditions Does It Prefer In My Garden?

Provide it with warm 15-27C temperatures, dry but relatively high humid conditions (around the plant) at night, and shade and cloudy days and it is most happy. Cloudy conditions limits UV damage to the fungus.  Even in the cleanest gardens, outbreaks can begin from spores spread by windblown rain, or on the feet of insects and birds. Rain actually washes away any spores floating in the air and can also prevent the spores from germinating, developing and spreading. 

I Use Milk Spray As A Preventative And Powdery Mildew Treatment

There are as many treatments for Powdery Mildew as there are types of milks! The most popular treatment, and the one I use here on the Balcony, is the milk spray. I'll leave you to investigate all of the others, right now let's talk about the one that works for me and many gardeners around the world. 

• Milk should be full cream (need the protein, don't use soy or almond etc)
• There is evidence that stronger milk spray solutions are more effective than weaker. I use around 3 parts milk: 7 parts water ratio, and others quote 1 part milk: 10 parts water. Too strong a brew and you might create an environment that encourages other fungus to grow! So err on the side of conservatism to start and titrate it until you find what works in your situation. 
• 2 teaspoons of soda bi-carb added to a litre of the above solution also increases the alkalinity of the leaf surface and makes it inhospitable to the spores.

The research points to 2 ways in which the milk spray works to stop the mildew

• buffers the pH of the leaf surface so that it is inhospitable for mildew. Studies have shown that infected plants have a low plant sap pH. Raising the pH means the plant is well mineralised and sends out signals that do not attract fungus.
• produces free radicals and an antiseptic action through an antimicrobial component in the milk (Lactoferrin)

These two actions makes milk spray a fabulous natural gentle and eco-friendly method.

How To Apply The Milk Spray

Once plants are heavily infected, it’s very difficult to get rid of the disease, so focus on preventing it from spreading to other plants. Remove any heavily infected leaves. These are unlikely to recover and the damage to the cell structure has already happened. Throw these leave out, don't put them in the compost bin as the heat generated is not enough to kill the spores.

In order to be effective, milk sprays must be used preventively, must be applied in bright light, and should be repeated every 10 days or so. Ensure the leaves are covered entirely with the spray, enough to cause dripping to ensure total coverage is best. Only spray during bright day time hours so that the milk dries or you stand to exacerbate the problem with other diseases that multiply in wet conditions if the leaves sit damply in the evening.

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A Final Word...

A healthy plant is a happy plant. A plant able to access all it's nutritional needs will be fortified to fight pests and diseases. Sustainable farming works with nature to keep crops, pests, diseases, weeds, and soil life in balance. 

Plant resistant varieties

Space plants correctly

Plant at the right times

Build healthy soil. Healthy soil provides a home to friendly insects and helps prevent many plant diseases.