Powdery Mildew

Curious about that white fungus on your plants?  The fungal disease powdery mildew affects a wide variety of plants and takes away the plant’s nutrients.  This is not normally considered fatal to plants, it can cause an overall decline in plant health and vitality and can affect the quality of quantity of flowers, fruits and veggies.

This year has been exceptionally bad for powdery mildew.  The pathogen over-winters on fallen leaves, with the spores spreading during wet weather in the spring.  The spores are continuously produced and spread by wind and rain and further infect other leaves during warm, humid weather.  That seems to describe our weather this year!

Identification:
– plants look as if they have been dusted with flour
– covers the top surface of leaves and flower buds causing the leaves to crumple and become distorted
– usually covers the upper part of the leaves, but may grow on the undersides as well
– young foliage is most susceptible to damage

Control:
– remove all the infect plant parts and destroy them (no compost!)  This will help to remove the spores so they don’t reoccur the following spring
– spray infected plants with a fungicide

Prevention:
– choose plants that are resistant or tolerant to powdery mildew (many mildew-resistant varieites of vegetables or roses have been developed)
– avoid watering plants from overhead in order to reduce relative humidity
– ensure enough spacing between your plants
– don’t overfertilize your plants
– prune overcrowded areas to increase aeration
– spray your plants with fungicides before any signs appear

Susceptible Plants and Veggies:

  • Begonias
  • Sunflowers
  • Chrysanthemums
  • Dahlias
  • Roses
  • Zinnias
  • Melons
  • Squash
  • Lettuce
  • Cucumbers
  • Potatoes
  • Parsley
  • Pumpkins
  • Grapes
  • Peppers
  • Tomatoes
  • Various Fruit Trees

Home Remedy:
– combine 1 Tbsp baking soda and 1.2 tsp of liquid, non-detergent soap with 1 gallon of water and spray the mixture liberally

Products available at Dufferin Garden Centre:
– Safer’s Sulphur Dust (Fungicide)
– Concentrated Lime Suphur