Powdery Mildew

Poking around the office garden today and I discovered our beautiful cucumbers all have a bit of powdery mildew. Rather than go back inside and get back to my email I spent a bit of time with them hoping to prevent the spread.

I thought I’d share my tactics, and ask you to share your tactics, and together maybe we can defeat the powdery mildew.

What is powdery mildew you ask?

It is a plant disease that will kill off the leaves and flowers of your plant. First you will notice little white or grey spots on your leaves and stem of the plant, then they will begin to turn yellow and shrivel up. The flowers will also shrivel and fall off the plant.

The book, The Rhodale Vegetable Garden Problem Solver, explains:

Powdery mildew spores germinate on dry leaf surfaces when humidity is high; the spores can’t germinate on wet leaves, and they don’t germinate very well on leaves in full sun. Thus, the disease tends to be a problem in dry climates or during dry spells, taking hold in areas of dense, shaded foliage where air circulation is poor. pg. 337

Leaf with Powdery Mildew

How do you know if it is Downy Mildew or Powdery Mildew?

The two are quite similar, however downy mildew happens during long periods of wet, cool weather. It happens very quickly and your plant will look like it has been frosted overnight. The symptoms look quite similar, however the furry spores appear on the underside of the leaf instead of the top of the leaves and the spores disappear when it is dry.

Milk and Water spray

So this is what I do.

First I take off all the diseased leaves. Sometimes I leave the really big green leaves that have one or two spots on them. I have a feeling this is probably not a good idea, as they host the spores, but I just can’t bear to throw away those lovely leaves. I’d recommend taking off all the diseased leaves if you can bear it.

Then I spray the leaves and stems of the plants with a mixture of 1 part milk to 9 parts water. I try to do this everyday.

I have also read that baking soda mixed with water, and compost tea or comfrey tea are also helpful.


Get rid of diseased plant material. If you don’t have a hot compost pile that will kill off the spores, then find somewhere else to dispose of the plants. The spores will overwinter and are spread by the wind.

Do you have any tips? Send them in at halifaxgardennetwork@gmail.com


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