My World of Moisture

Powdery Mildew – An Experiment in its Control

I am getting a bit worried about the current weather. Staying with a gardening theme and fungi, we are having the type of weather that these microbes love. Days of showers and not enough sunshine to dry the ground. On top of that, the night time temperatures are sitting around about 11 to 13 centigrade. Very mild, damp and favourable for certain types of fungi. In my last post on this blog I talked about the fungi responsible for “damping off” by attacking young plants. This time my focus is on another troublesome fungi that attacks both mature and young plants, the dreaded “Mildew”.……..

Powdery Mildew

To give it its full name, “Powdery mildew” is a group of fungi that infects different types of plants. According to The Royal Horticultural Society website there are a number of species of powdery mildew and each has its own target plant. Whatever species are lurking around our garden there’s one that likes our courgette plants. Every year some of the plants end up with their big leaves completely covered in white patches of the fungus. Some years are worse than others and guess what, a grey damp June to July is devastating for the plants.

Courgette Leaves

Courgette Leaves

Fighting back

Time to fight back! In my previous post I described how limiting moisture around young plants can help tremendously in keeping damping off fungi controlled. My advice was to keep the surface around the base of the stems dry and the plants well ventilated. Of course this is not possible in open ground and the weather at the moment is keeping humidity levels high. So, what’s my plan of attack?

When I wrote about potato blight, another type of fungus, in my eBook A Wet Look At Climate Change, I discovered that one of the first treatments to kill the blight was copper sulphate. This was sprayed onto the crops. Copper in solution is toxic to yeasts and fungi. Also toxic to us in big enough quantities, so I would not advice or recommend this as a treatment. Actually there are no legal chemical fungicides for edible plants. But, the scientist in me prevails, and as we at home are the only ones eating our courgettes, then an experiment with copper sulphate had to be tried.

Chemical versus non-chemical

A dilute solution lightly sprayed onto the leaves avoiding the fruiting shoots seemed to give some protection from mildew. However not being that happy using copper I was on the lookout for non-chemical remedies. Last year Dee Sewell, a qualified horticulturist, posted on her Greenside Up blog a reply to a query about mildew. Dee said to try spraying with a dilute milk solution. I contacted Dee and she thought a 1:3 dilution of milk in water might work.

Let battle commence

We planted six courgette plants in a row so that they will all get the same amount of light. Also they are in the open so are well ventilated. There are no overhanging branches or shade of any sort. When the weather permits me, that is, with a long enough break between the showers to get some sunshine, I’ll spray the plants. Hopefully the spray will dry in the sun before the next shower washes it off. A nice sunny day would be welcome in more ways than one!

Courgette plants

Our courgette plants


Spray the courgette plants in the picture starting with the one nearest with copper sulphate solution and then the next one along with milk solution. Carry on spraying alternate plants with the copper or milk solution. That way the position of the plant should not be a factor in the outcome of mildew or no mildew. I think I’ll repeat the spraying every two weeks.

Watch this space for the result…….

If you would like to hear more about moisture in everyday life, please sign up for email alerts of my blogs.

Useful background and various topics on moisture and humidity are discussed in my eBook “A Wet Look At Climate Change”.

Welcome to my world of moisture


Basil Rescued from a Nasty Fungal Death


The Frizzing Humidity


  1. Nice Post. Thanks for sharing this detailed post with readers. It is very helpful. We can use the UV technology for treating the powdery mildew.

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