An ounce of prevention is worth a pound of flowers.

Every year outdoor plants look great through the spring and summer. But when summer fades, days shorten and nights cool,  plants become more susceptible to powdery mildew (PM). At the least PM is unsightly, but on consumable plants it can be unhealthy. Prevention is key to fighting this disease.

Preventative Measures You can Use in Your Garden

  • Avoid excessive nitrogen in your fertilizer. Nitrogen near the end of summer will encourage new leaf growth and young leaves are more susceptible (even though you might find on old leaves first)
  • Avoid Shade. Powdery mildew does not like al ot of light. Shaded plants or plants that are overcrowded are more likely attacked. Start pruning to allow more light onto all of your plant.
  • Increase Air Flow. Powdery Mildew is also sensitive to air flow so another good reason to prune.
  • Be More Attentive to Watering.  Water early in the day. Avoid over watering (but be careful, drought stressed plants are susceptible). Mulch around the base of your plant can help reduce splashing which may help PM spores travel to you plant. There is some controversy about whether it is beneficial to sprinkle water on your plants but we think it is best to avoid the practice.
  • Keep Your Gardening Tools Clean. When pruning (or other activity), sterilize your tools in a little 5% bleach solution regularly when moving from plant to plant.


What to do When You See PM

PM spores travel by wind and spread easily when conditions are favourable. PM likes moderate temperature, slightly humid weather and does not need water to germinate.

  • As soon as you see PM begin treatment.
  • Carefully remove infected leaves and throw out – do not compost
  • Badly infected plants should be removed in entirety.
  • The most available treatment is usually a sulphur based spray. Sulphur can prevent spores from germinating. It also kills fungi on contact. Follow label directions and test to ensure your plant does not have a phytotoxic reaction.
  • Copper based sprays can be very helpful if used as a preventative about 2 weeks prior to when powdery mildew usually comes or as soon as it appears.
  • In addition, you may find homemade remedies on the internet that can help control PM by changing the pH on the plant leaves. Your mileage may vary with these concoction.

Prepare your plants now. The tools you should have on hand include pruners/trimmers, and a suitable fungicide spray, and some bleach.


August 27, 2020 — TREVOR WILKINSON