First appearing as faint white spots on leaves, this fungus gradually forms a white dusty film over the entire surface.
Thriving in times of high humidity and dry conditions when temperatures are 11 to 28°C, powdery mildew can spread to the buds, stems and fruit if conditions are favourable.
It’s a common problem where plants are deficient in nutrients. They may have exhausted their fertiliser supply, or can’t absorb nutrients as the soil is too dry.
All powdery mildews like the same conditions but different fungi infect different plants, so the mildew on sweet peas won’t spread to roses.
House plants that are susceptible to powdery mildew include African violet, begonia and jade plant.
Snip off any diseased parts, dipping the secateurs in a weak bleach solution between cuts, and throw in the rubbish, not the compost.
Mix one tablespoon of bicarb soda with three drops of dishwashing detergent in four litres of water, and spray plants every five to seven days.
TIP Arrange pots to have lots of space around them to increase airflow.
Methods of control
Spray foliage with a seaweed emulsion diluted at the recommended rate to give the plants the micronutrients they need to help resist these fungi.
Planting too close together can assist the spread of powdery mildew as airflow is reduced. Try thinning and pruning plants to create space and water plants at soil level to avoid the fungus being spread by water splash.
On lawns, it looks like a dusting of white powder on the top of leaf growth and in severe cases it can kill the entire lawn. As soon as it’s noticed, spray with a fungicide, choosing a product containing neem oil, sulphur, potassium bicarbonate or copper.
DIY organic remedy
Mix one cup of full-cream milk with 10 cups of water and stir well.
Spray plants with the milk solution as soon as the first symptoms are noticed then regularly every seven to 10 days or every 14 days if it is hot.
Make sure to cover the entire plant, including the upper and lower sides of the leaves and coat the stems.
TIP Stick to the quantities given, as using too much milk can cause a black growth called sooty mould to form.
Common victims of powdery mildew
- Crepe myrtle
- Hydrangea
- Ajuga
- Photinia
- Sweet pea
- Zinnia
- Apple
- Grape
- Rose
- Strawberry
First appearing as faint white spots on leaves, powdery mildew gradually forms a white dusty film over the entire surface. Image: Getty Images