Powdery mildew
Powdery mildew is the name of a variety of fungi, that affect the leaves of plants. They are present everywhere in the environment and are brought in by wind, birds and insects. Powdery mildew loves warm humid nights and dry, warm and shady areas of the garden. Really wet conditions and constant very high or very low temperatures are actually not the conditions where the fungus thrives.If the conditions are right, once spores of the fungus reach a suitable host they grow into the leaf and start to feed on the plants nutrients. The infection becomes obvious when we see leaves covered with irregular white or grey, furry or powdery patches most often on the top sides of the leaves. Leaves go yellow, wilt and dry out.The presence of the fungus eating ladybird is always an indicator that there is a problem. It feeds on the mildew, but it will never be able to contain it.
which plants are affected?
There are several sorts of powdery mildew affecting different plants, but they are all causing the same problems and can be treated the same way. Plants especially susceptible to powdery mildew are the gourd family (melons, squashes, zucchinis, cucumbers). The fungus also attacks the legume family (peas, beans), rosemary, strawberries and the nightshade family (tomatoes, capsicum, eggplant, chili).
how to avoid powdery mildew
Powdery mildew is a fungal infection, distributed by fungal spores. The fungus favours warm moist conditions to set foot onto a plant and warm dry conditions to thrive.We can't control the presence of fungal spores and we can't control the weather conditions but there are some basic rules that help reducing the risk:
always water early enough for the leaves to dry off again, water the soil, avoid wetting the leaves,
do not overcrowd beds, make sure there is plenty of air circulation,
avoid over-fertilising with nitrogen in warm weather conditions. It leads to leaf growth and bad air flow,
remove some leaves and thin out plants in warm weather conditions, allow for air flow,
wash tools and hands after dealing with fungi
apply diluted worm juice twice per month to strengthen plants,
once a week, apply milk-spray as a preventive measure.
dealing with powdery mildew
Once a leaf 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:
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-can1 tbsp of Eco-fungicide powder1.5 tbsp of vegetable oil1 dash of liquid soap5 liters of water
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-can2 tbsp of baking soda1.5 tbsp of vegetable oil1 dash of liquid soap5 liters of water
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-can0.5 l of milk (low fat or full, doesn't matter)4.5 liters of water