Milky Fungus on Plant Leaves

Causes of plant disease

Found a milky white, or grayish powder-like fungus on your plant? Fungi are the most common cause of plant disease in all parts of the United States. The most likely culprit is a wide-spread disease called Powdery Mildew, which spreads via water and wind.

Symptoms of Powdery Mildew

According to the Cornell University Plant Clinic, "Injury due to powdery mildews includes stunting and distortion of leaves, buds, growing tips, and fruit... Yellowing of leaves and death of tissue may result in premature leaf drop."

Susceptible Plants

Lilacs show some resilience

Powdery mildew often infects chrysanthemums, roses, phlox, dahlias, begonias, African violets, some fruit trees, sycamore trees, squash, beans, and peas, although lilacs have shown some resilience to the disease.

Prevention: Make Your Own Spray

Where possible, remove and destroy any affected plants or plant parts. Make your own preventative spray by combining 2 tsp. baking soda, 2 tsp. of summer oil (a refined horticultural oil) and a gallon of water. Spray leaves and plant parts regularly.

Chemical Preventatives

Use other agents to protect your plants from infection, including: insecticidal soap, lime sulfur, and/or a chemical agent called triforine (bayleton) used frequently by rose growers, reports Western Garden Book.

Already a Problem?

Save your houseplants or ornamentals by trying fungicides such as neem oil, potassium bicarbonate, lime sulfur, or sulfur--depending on the severity and type of plant infected. Stronger products, requiring mask and gloves, include: tridimefon (bayleton) a wettable powder or Triforine a liquid systemic.Many other chemicals are available to eradicate powdery mildew; always check labels to be sure the product is safe for use on your plant.

Contact Your Extension Office for Fungicide Information

For more information on the latest product to use for your plant, contact your local Cooperative Extension Office. For a state by state listing of Extension Offices near you, go to csrees.usda.gov/Extension.

References

• Western Garden Book; Sunset Books and Magazine; 1997, p. 540
• Cornell University Plant Clinic

Resources

• United States Department Department of Agriculture, Listing of Cooperative Extension Offices