|Powdery mildew affects a wide variety of plants
Image: Julie Vader
Powdery mildew affects the leaves and stems of a wide variety of plants. Early signs are small white spots on the front and back of leaves, but powdery mildew soon covers foliage, making plants look like they’ve been doused in talcum powder.
Left untreated, this infection is unsightly, stresses the plant and ultimately leads to lower yields, and may eventually cause plants to die. The good news is that powdery mildew is treatable – find out how below.
Powdery mildew refers to a wide array of related fungi which attack leaves stems and flowers. Individual varieties of fungus usually only affect a narrow range of plants, so just because your geraniums show signs of infection, doesn’t mean your courgettes will get it too, although cucurbits like courgettes, squashes and pumpkins do tend to be susceptible to powdery white mildew.
Although it looks bad, powdery mildew is a superficial infection – it doesn’t kill the leaf directly, but feeds on sugars within the leaf and prevents the sun reaching the plant surface. Over time this weakens the plant.
|Speckled white spots on leaves indicate powdery mildew
Look for small white spots on both the surface and the underside of leaves, or more widespread “dusting” of foliage, flowers, and even fruit. Unchecked, powdery mildew spreads fast and may cause leaves to distort, discolour, and eventually die.
Easily recognisable on most plants, nevertheless, check carefully – the sooner you treat an infection of powdery mildew, the better.
|Stop the infection from spreading by removing the damaged leaves
Treatment options for powdery mildew range from physically removing the infected parts of the plant, to using proprietary and home-made sprays.
If you decide to prune out infected leaves, you should dispose of them by burning or putting in your rubbish bin. Heaping fungus infected foliage on your compost heap only creates a repository for fungal spores which will be ready to reinfect your plants next spring.
Home treatments for powdery mildew include:
To treat powdery mildew with a proprietary spray, it’s important to follow manufacturers’ instructions, and if you’re treating fruit or veg crops, do check the spray is suitable for use on edible plants.
|Watering the roots and not the leaves will help deter powdery mildew
Warm, wet weather, poor ventilation, and water stress encourage fungal infections, but there are some things you can do to deter powdery mildew.
By taking steps to prevent and treat powdery mildew, you’ll soon get on top of the problem.