Powerering out Powdery Mildew

By Melanie Mathieson
Gardening Guru

Many gardens have at least one plant infected with powdery mildew each season and with the extra moisture this season powdery mildew can get right out of hand on some plants. Powdery mildew is a fungus growing on the surface of the leaves of broad-leaved trees and shrubs and herbaceous plants in your gardens. Powdery mildew does not kill the plant that it has infected but it can affect the general health and appearance of the tree, shrub or plant.
There are four different species of this fungus found in central Canada and all have the same grey powdery or dusty looking fungal growths on the surface of the leaves and with a magnifying glass you may be able to spot small black or brown fruiting bodies within the powder. The spores produced in the fruiting bodies of the fungusdo not need moisture to reproduce but do need wind to help them disperse and infect other plants.
The first signs of powdery mildew isthe look of a chalky white or grey dusty mould on the surface of the leaves of the infected plant. As the disease progresses and worsens, in the right conditions, the leaves can begin to distort and eventually fall off of the plant. You will find most plants in your garden that are affected are in the shadier areas of the yard or garden. Often areas of the yard or garden with poorer air circulation and shelter from other plants will be infected more often than those plants situated in sunnier and more open areas within the yard.
Powdery mildew can affect almost any plant with green broad-leaves but there are some plants that seem to be more susceptible to infection thatothers. Conifer trees and shrubs are not susceptible to infection from powdery mildew but these commonly are; poplar and willow trees, lilacs, snowball, viburnums, many species of roses, creeping vines, delphiniums, yarrow, black-eyed Susan’s, Echinacea, zinnias, asters, bee balm, phlox, coreopsis, and vegetables like, beans, peas, cucumbers, squash, pumpkins and gourds, watermelon and cantaloupes. Powdery mildew can also be found on the surface of the fruit, vegetables (peas) and seeds that some of these plants produce. Powdery mildew can get on the surface of the skin of apples giving the skin a crackled brown pattern. But gardeners behold all is not lost, there are many new cultivars and varieties of many of the plants mentioned above that have been hybridized to resist powdery mildew. When picking new plants for your garden look for a “powdery mildew resistant” statement on the package, label or hangtag with the plant.
The outbreak of powdery mildew can also be affected by the weather as it does prefer moister, more humid conditions rather than long hot dry spells during the summer months. The conditions are controllable and with a little work you can get a handle on the infection. The first and maybe most important step is good housekeeping of the yard and garden. Spores from this growing season can overwinter on plant debris and leaves from the plants of this year. You can also find spores overwintering on fruit fallen to the ground, spent buds and flower heads of this season’s flowers and in perennial weeds you many have growing in or near your yard. Remove all of this type of debris and keep vigilant about removing vegetable plants from the garden once they are done producing. If the debris you are removing from your yard and garden is infected with powdery mildew already do not add this to your composter, by doing so you may habour the spores in the composting soil and will reinfecteverything when you add the compost to the garden. Instead place all of the infected plant debris in a garbage bag, seal it up and have it taken away. Make sure you do this with the leaves of any shrubs or trees that were infected in the growing season as well. The leaves from other trees not infected with powdery mildew, can certainly go into the composter or on the garden in the fall. Without this thorough cleaning in the fall time many spores will harbourover winter and multiply in the spring and be redistributed by the wind making next year’s outbreak worst than the last.
Again you must keep up the garden housekeeping throughout the growing season as well. Make sure you cut back spent flowers and perennials as they die back. If only a few leaves of a plant are infected you can remove them and dispose of them properly. Clipaway dead foliage at the base of perennials to ensure good air circulation.
Plants under stress are always more susceptible to disease and insect infestations so make sure you have a healthy garden. Keep plants well watered and fertilized throughout the season, especially in dry or drought conditions, as this helps prevent or reduce stress on the plant. Do not however, fertilize plants when they have a moderate to heavy infestation of powdery mildew as this will encourage the plant to put all of its energy into growing lush and not fighting off the fungus. Water plants early in the day and water at the base of the plant if you can, to avoid getting water on the leaves.
Even after diligent housekeeping in the garden you may still find some powdery mildew, especially if the conditions are prime.
There are limited commercial treatments available at your local garden centre today, but most are formulated for a wide variety of fungi and can be quite ineffective to some fungi while very effective on other species of fungi. If you are going to purchase a commercial product I recommend a fungicidal soap instead of some of the other products available.
More economical, more environmentally friendly and best of all the most effective treatment comes from a recipe that you can make at home with common ingredients. If you want to “power out powdery mildew” you need to add one tablespoon baking soda, one tablespoon of dish soap (soap is so the solution clings to the leaves) to one gallon of warm (not hot) water. Stir well until soda has dissolved and transfer to a hand held spray bottle. Apply directly and generously, by spraying directly, the affected areas of your plants every few days, especially after a rain. This will help kill those spores and get things under control.
With some good housekeeping and a great homemade and organic, environmentally friendly recipe to apply to the infected areas you will be able to power out powdery mildew in your garden.