Does Powdery Mildew Stay in Garden Soil for a Long Time?

Plant Symptoms

• Powdery mildew can affect almost any kind of plant. The fungus covers the surface of leaves with a white or grayish, powdery growth. Often, stems, buds, flowers and fruit also become infected. Leaves may turn yellow and fall and buds may not open. Young, succulent plant growth is more susceptible than older growth. Although the fungus is unsightly, it rarely causes severe damage or kills plants.

Fungus Lifecycle

• The fungi that cause powdery mildew require the plant species that they infect to survive. Powdery mildew fungi don't invade their host, they produce fungal threads (mycelium) on the outside surfaces of leaves or stems. They feed on the plants by sending rootlike structures (haustoria) into the top cell layer of the plant. The powdery mildew fungi overwinters by clinging to plant debris. In spring, fruiting structures of the fungi produce spores, which can be carried by wind or splashed by rain onto new host plants.

Non-Chemical Control

• Shade favors powdery mildew, so grow susceptible plants in sunny areas. Avoid excess or late summer application of fertilizer, because it may produce succulent growth favored by powdery mildew. A slow-release fertilizer is a better option. Improve air circulation by pruning or spacing plants farther apart. Poor air circulation increases humidity and rate of fungal infection. Removing infected plant material and plant debris in fall will help reduce powdery mildew infections.

Chemical Control

• Several horticultural oils are effective in preventing and eradicating powdery mildew. Sulfur sprays are best used as a preventative. A nontoxic spray made of baking soda and lightweight horticultural oil (1 tablespoon baking soda, 2.5 tablespoons oil in 1 gallon of water) was found to effectively combat powdery mildew by researchers at the University of Rhode Island.