Impatiens Downy Mildew & How to Avoid It
What is Impatiens downy mildew (IDM)?
Impatiens downy mildew is a disease that affects Impatiens walleriana. It is a serious issue in the United States and has limited the use of impatiens in gardens and containers in recent years.
What does IDM look like?
Symptoms are first seen on leaves near the tips of branches and include an irregular yellow-green discoloration of leaves. Stunting and reduced flowering are other common symptoms. The most distinctive characteristic is a fuzzy white material that develops on stems, buds and the undersides of leaves.
IDM is caused by a fungus-like water mold called Plasmopara obducens. It takes the form of specialized spores called oospores found in the soil and on infested plants.
How can I save a plant with IDM?
Plants with IDM are unlikely to recover and can infect other impatiens plants. If you see IDM, remove the plants (roots and all), place them in sealed plastic bags and throw them away in the garbage. Also consider removing all impatiens within a three-foot radius of the plants, as they are likely infected but may not be showing symptoms. DO NOT use fungicides on plants that are showing symptoms, as they won’t be effective.
How can I include impatiens in my garden and still avoid IDM?
You can find disease-resistant varieties of Impatiens walleriana that are now available at your local garden center. Testing and trialing have proven that Beacon® Impatiens offer high resistance are highly resistant to Impatiens downy mildew. Available in a wide range of colors and mixes, Beacon Impatiens bring long-lasting color to your shaded gardens and containers without the risk of disease.
Space impatiens plants about 10-12 inches apart to promote good air flow and create drier conditions that are less favorable for IDM development. Water the soil around the plant (so the roots of the plant can take up the water) rather than watering from overhead, so the flowers and leaves are not soaked. A soaker or drip hose can work well to do this.