How to Remove Black and White Mildew From Plants

Powdery mildew fungi are host specific, with each species only infecting certain plants.

Several fungal infections can infect plants. Two of the most widespread are sooty mold and powdery mildew. Sooty mold is a dark gray to black fungus that feeds off the honeydew that sap-sucking insects such as aphids, scales or whiteflies secrete. Sooty mold can cover leaves and prevent them from photosynthesizing. Powdery mildew is a white fungus that feeds off plants and can, if left untreated, cause leaf drop and even death.

Things You'll Need

• Insecticide
• Fungicide

Instructions

Sooty Mold Control

1. Wash plants with water. Since sooty mold feeds on honeydew excreted by insects, you'll need to control the insects before you can control the mold. Washing the plants with a jet of water from the hose can knock insects off the plant, remove honeydew and begin to rinse off the mold. Once insects are under control, the mold will weather away on its own.

2. Apply insecticides. To help quickly control insects and get rid of sooty mold, horticultural oils, insecticidal soaps or chemical insecticides may be necessary. Be sure you use a product appropriate for your plant and for the type of insect infesting it. Follow manufacturer's directions carefully.

3. Prevent future infestations. Once you have the initial infestation under control, sooty mold will have nothing to feed on and will die. To prevent future sooty mold problems, keep your plants healthy with the proper amounts of water and fertilizer, keep your garden weed free and regularly inspect your plants for insect pests.

Powdery Mildew

1. Remove infected stems, branches, twigs and leaves. Any heavily infected part of the plant needs to be removed and destroyed by burning or throwing it in the trash. For infected annuals or vegetables, remove and destroy the plant, including the roots, in the fall. Any debris left in your garden may cause a new infection in the spring.

2. Irrigate with caution. Wet leaves cause humid conditions that can help the fungus germinate. To avoid spreading powdery mildew, avoid wet leaves.

3. Prune excessive vegetation. Overcrowding in the garden can decrease airflow and increase humidity. These conditions help powdery mildew germinate and spread so pruning infected plants and removing some plantings from your garden may help control the fungus.

4. Keep your plants healthy. Using the proper amounts of water and fertilizer for your plants can help them fight off and thrive with a fungal infection. Be careful not to overfertilize as it causes an excess of succulent growth that fosters powdery mildew.

5. Apply fungicides. Fungicides should be used along with cultural methods to obtain the most satisfactory results. Products containing sulfur, neem oil or myclobutanil and horticultural oils, for example, can be effective. Read labels carefully to be sure the product you use is registered for use on your variety of plant, and always follow the manufacturer's directions.

Tips & Warnings

• Don't compost materials infected with powdery mildew. Composting temperatures may not be high enough to kill the fungus.

References

• University of Florida IFAS Extension; Black, Sooty Mold on Landscape Plants; Alicia R. Lamborn
• Colorado State University Extension; Powdery Mildews; B. Edmunds, et al.; May 2009
• UW Extension; Sooty Mold; G.L. Worf, et al.; 1995
• Clemson Cooperative Extension; Powdery Mildew; Chuck Burgess; September 2005