Powdery Mold on a Jasmine Plant

Symptoms and Damage

• The earliest symptom of powdery mildew is small, circular white spots. Eventually the white spots expand and coalesce, becoming a continuous mat of mildew that appears as a dusty white or gray coating on leaf surfaces and other plant parts. Rubbing the leaves can remove at least some of this growth. Symptoms are most prevalent late in the summer on plants kept outdoors but can appear year-round on indoor plants if humidity and temperature are high enough. Infected plants may be stunted and have distorted leaves, buds and growing tips. The jasmine may also suffer from yellowing leaves and leaf drop.

About the Disease

• The fungus that causes powdery mildew spreads by spores that are produced within the white patches. Wind blows spores to other plants or parts on the same plant where they become established if conditions are suitable. Additionally, the fungus can produce hardy structures, known as cleistothecia, that can overwinter before releasing spores in the spring. The fungus survives the winter attached to plant parts and debris -- this ability indicates the need for removal of such debris as part of a management strategy.

Cultural Control

• You should observe several cultural practices to limit the presence and effects of powdery mildew. Reduce relative humidity by avoiding overhead watering and prune out crowded plants to improve air circulation. Avoid applying fertilizers late in the growing season. Supply nitrogen at this time to promote the growth of susceptible tissue. Remove and destroy all infected plant parts. Composting generally does not destroy the fungus.

Chemical Control

• If powdery mildew is proving difficult to control with solely cultural means, fungicide may be used. For best results, combine cultural controls like removal of debris with the use of a fungicide applied every seven to 14 days throughout the growing season. Possible active ingredients that can be used to address powdery mildew include sulfur, triforine, neem oil and potassium bicarbonate. Combine baking soda and lightweight horticultural oil in water to make a homemade alternative control.