Dealing with powdery mildew

Once a leave is seriously infected it needs to be removed. It can go into the compost because the spores are around in the environment anyway. We can’t remove the spores, but we can make the conditions less favourable for the fungi.

We use different approaches and are still testing which works best for us. All of them are spray-on treatments. They should be used when first signs of mildew are present. The third should also be used as a preventive measure for susceptible plants in mildew prone weather conditions.

First some very important notes on how to use these treatments

  • these sprays are not at all toxic to humans, so don’t be concerned if it hit’s your skin
  • wash tools and hands after dealing with fungi
  • make sure you mix and dissolve the ingredients in the spray-can
  • spray top- and downside of the leaves and all of the rest of the plant, it’s important to cover everything
  • don’t spray too early in the day. Never spray in bright sunlight because this will burn the leaves and cause more damage than it helps. Spray in the late afternoon
  • don’t spray too late in the day. The leaves need to dry off before nightfall, otherwise you are inviting the spores in by offering a humid night environment. Spray in the late afternoon
  • spraying needs to be done consistently, once per week and after every serious rainfall until the mildew disappears
  • make a note in the garden log book about what you applied and where, so following gardeners know where to pick up the work
  • always rinse the spray-can and its hose. It’s hard to fix it, if it gets clogged up

Here are the recipes:

  1. A commercial product called Eco-fungicide. It basically contains potassium bicarbonate which changes the micro-climate on the leaves to less acidic which doesn’t seem to suit the fungus. It is mixed with oil, which makes it stick to the leaves and some soap, to help the oil and the water mix.
    Thoroughly mix in the 5 litre spray-can
    1 tbsp of Eco-fungicide powder
    1.5 tbsp of vegetable oil
    1 dash of liquid soap
    5 liters of water
  2. Our homemade version of the commercial product. We use baking soda instead. It’s sodium bicarbonate and should be similarly effective in making the environment on the leaves less acidic and hence less attractive for the fungus.
    Thoroughly mix in the 5 litre spray-can
    2 tbsp of baking soda
    1.5 tbsp of vegetable oil
    1 dash of liquid soap
    5 liters of water
  3. Milk spray as a preventive measure and as a treatment. There is no scientific proof but strong evidence that milk proteins broken down by sunlight have a fungicidal effect similar to synthetic fungicides. This spray needs to be applied to all susceptible plants, already affected by mildew or not, whenever weather conditions offer warm moist nights and dry warm days.
    Thoroughly mix in the 5 litre spray-can
    0.5 l of milk (low fat or full, doesn’t matter)
    4.5 liters of water