Powdery mildew is showing up in an area of my garden that gets very little water. How can I get rid of it?
You may be surprised to discover that powdery mildew isn't activated by excessive moisture, so the fact that it's decided to turn up in a section of your garden that's water-deprived is not really all that surprising.
Temperature plays a far greater role in the spread of this fungus, which is why you're suddenly noticing it spreading like wildfire through susceptible plants now that we’ve hit late summer. The constant shifting of temperatures between the warm highs of daytime and chilly lows of night allows powdery mildew to thrive.
The list of plants affected by this fungus is wide ranging and includes beans, onions, cucumbers, squashes, delphiniums, phloxes, roses, zinnias, begonias, grapes, strawberries, catalpas, lilacs, maples, hawthorns, firethorns, apples, turf grasses – and the list goes on. It attacks the leaves, shoots, fruits and blossoms and although these late season flushes are rarely fatal, they can slow plant growth, turn leaves yellow, hasten the decline of flowers, reduce yields and make your garden look vaguely apocalyptic.
Gardeners tend to be divided on whether or not to take steps to control powdery mildew since it's so ubiquitous and no matter how valiant their efforts are, it continues to return year after year. The problem is that the spores are spread by wind and no matter how well you control an outbreak in your own yard, spores will continue to blow in from other gardens in the neighbourhood. Some gardeners choose to put the effort into controlling the problem knowing they likely won’t be able to eradicate it while others shrug and move on to other things. If your garden is located next to a shrugger’s, you’re pretty much beat.
The best way to avoid powdery mildew is to plant resistant varieties and to make sure your plants are given good air circulation and lots of sun. The healthier a plant is, the less susceptible it will be to disease in general, so taking the time to improve your soil is never a lost cause.
Once powdery mildew does show up, the best way to control it is to remove and destroy infected plant parts as soon as you see them. With minor infections, you can also hit affected leaves with a steady stream of water to knock off the powdery coating. Do this early enough in the day that the leaves have time to dry before evening.
Don't put any plants or plant parts infected with powdery mildew in your compost pile or the spores will happily overwinter and turn up in your garden again next year.
If you have any questions or comments, please send them to me at vanessa@gardenmuse.ca.
