Tips on Controlling Powdery Mildew in your Garden

This is one of the best times of year to be out in the garden – many of the new annuals are freshly planted, the veggies are in and growing and the lawn looks awesome…

But it is also about the time that we start to fret about mildews – that annoying group of fungal diseases that bother some of our favourite plants.

So – a few bits on Powdery Mildew which is, as it is so aptly named, a whitish powder that gets on the leaves of many plants – roses and phlox leap to mind.  The good news is that powdery mildew, while disfiguring, is usually not fatal for the plants and there are a number of home remedies that you can try.

Here is a list of things to think about as you try to control powdery mildew on the above-mentioned rose and phlox:

• Dormant oil in late winter – it's too late now, but a spray of dormant oil on the rose stems will help knock down a few spores of mildew.
• Sanitation – be rigorous in picking up fallen leaves and pruned stems from around phlox and roses as they can harbor spores. On a related topic- roses benefit from a twice a week morning ‘shower’ to keep spores off the leaves – but avoid wetting the foliage in the evenings.
• Healthy plants – make sure you have the plants in the right locations so there is minimal environmental stress. For roses that means full sun – for phlox that means a cool location with maybe a bit of shade. Good air circulation is good to keep the mildew down – but make sure you have mulched the plants to keep moisture in the soil where it belongs.
• Healthy plants but not too healthy... Well, that makes no sense! The issue with powdery mildew is that it is often found in actively-growing ‘new growth’.  So for roses, in particular, one way to reduce mildew is to reduce how often you fertilize the rose bushes. Consider cutting your feed to half strength or half as often. Especially if your plants are nice and mature.
• Select mildew resistant varieties. With phlox, we see that the very old varieties and the very newest varieties seem to offer good resistance. There are some good lists online that will help. http://www.chicagobotanic.org/downloads/planteval_notes/no35_phloxpaniculata.pdf. Some of the breeders have introduced new phlox varieties that claim good resistance too!  Roses are trickier. The good news is that the shrub rose types have some great newer varieties that are good with disease – ‘Knockout’, ‘Drift’ and the neat new Canadian rose ‘Campfire’ are all great choices. Less good are hybrid tea type roses.

If you are able to have healthy and resistant plants in the right locations and keep the sanitation levels high you will be ahead of the game.

At Barrie's Garden Centre, we can a variety of products that can help you eliminate this from your garden. Sulpher Dust, and Bordo Copper Fungicide are just a few that are carried in-store. Ask any of our helpful staff for advice. Avoid spraying in hot sunlight as that can burn the leaves.