Nanaimo Magazine article

With the great growing weather we have had over the last two months, gardens in the Central Island area are thriving. While there has not been the usual abundance of aphids and mites courtesy of last year’s unusually cold winter, there are signs that Powdery Mildew and other Fungal diseases are beginning their infestation of specific plants. The majority of these diseases are genus specific attacking only certain plants. One of the most common diseases found in local gardens is Powdery Mildew. The symptoms include a gray mold like growth on the upper side of leaves followed by a curling of the leaves and finally a yellowing and total drying of the infected leaves. Perennials including Bee Balm, Delphinium, and Coreopsis, vegetables such as Squash, Zucchini and Cucumbers, Annuals including Verbena and Petunias, and Shrubs and vines such as Roses and Clematis are prone to mildew infestations. There are three methods of controlling the spread of this disease. First choose plant strains that are mildew resistant. Reduce the infestation level through the use of organic or inorganic fungicides. Option three is to control the environmental factors that enhance the growth of the Mildew fungus.

Plant Breeders are continuously producing new genera of plants that are preferred hosts of Powdery Mildew. While these new species may not have the same characteristics gardeners are used to, they are not a preferred host of the mildew fungus. When purchasing plants watch for labels indicating that the species is mildew resistant.

The mention of chemical control for some gardeners invokes images of the use of toxic materials. This is not the case for the control of Powdery Mildew. The most effective material used to control Powdery Mildew is Sulfur. It can be applied as a dust or a suspension. The preferable method of application is to spray the sulfur suspended in water. To improve the coverage, add a sticker/spreader such as Raingrow’s “Super Flow”. While spraying this mixture be sure to continually agitate it as the sulfur is not in a dissolved form and will settle to the bottom of your sprayer.

As an added precaution eliminate conditions that the Mildew spores find ideal to propagate. Remove any foliage that has symptoms, reduce the humidity around the leaves by first avoiding watering the foliage and second thinning the foliage so that air movement at the leaf surface can occur. Finally do not compost any plant parts that have been infected with Powdery Mildew as this practice will provide a good start for the disease next year.

Using all three methods will provide a mildew free healthy garden .