How to Get Rid of Black Soot & White Under Leaf Problems

Powdery mildrew can form on lilac leaves.

According to Ohio State University, controlling sap-sucking insects such as aphids will get rid of sooty mold. Aphids secrete "honeydew," a sweet liquid that encourages the growth of sooty mold on the leaves of ornamental plants. Powdery mildew is a fungus caused by warm temperatures and high humidity. OSU says, "Most powdery mildew fungi produce airborne spores and infect plants when temperatures are moderate (60 to 80 degrees F) and will not be present during the hottest days of the summer."

Things You'll Need

• Garden hose
• Teaspoon
• Gallon container
• Liquid soap
• Spray bottle
• Lady bugs
• Pruning shears
• Banana peels
• Chemical spray
• Garlic cloves
• Measuring cup
• Strainer
• Soaker hose
• Fungicide

Instructions

Nonchemical and Chemical Methods of Controlling Aphids

1. Spray a hard stream of water from the garden hose to wash the mold and aphids from the top and bottom of the leaf. Do this while the insect population is small and the soot affects only a few plants. Hard spray injures the insects and renders most unable to return to the plant. Nonchemical controls reduces the risk of killing beneficial insects.

2. Mix a teaspoon of liquid hand soap or liquid dish detergent with a gallon of water. Pour the mixture, as much as will fit, into a spray bottle. Spray the mixture over and under the leaves to remove the soot and kill the aphids.

3. Release natural predators purchased from a garden center on the plants. Lady bugs are harmless to people and pets but will destroy aphids and their larvae. Be aware that lady bugs are flighty. They'll remain in one place only so long. After a few days, they'll fly off to your neighbor's plants.

4. Scatter banana peels around plants in small backyard areas to repel aphids. Banana peels contain phosphorus and potassium and make good fertilizer.

5. Spray chemicals such as insecticidal soap, neem oil, narrow-range oil with a spray bottle to temporarily control aphids. However, these chemicals will also destroy beneficial insects.

Nonchemical and Chemical Methods of Controlling Powdery Mildew

1. Boil 10 cloves of garlic in 4 cups of water. Boil the water and garlic in a large pot on your stove. Remove the pot from the heat when the garlic turns to mush. Let the liquid cool, strain the mixture through the strainer and pour it into a spray bottle. Prevent mildew growth by spraying the plants when daytime temperatures start to warm and the nights are still cool.

2. Use pruning shears to prune out all dead and diseased leaves and wood from plants if the disease is already showing. Destroy diseased leaves, weeds, and twigs by burning or bagging for trash pickup.

3. Water plants once a week until the soil is wet 8 to 10 inches deep. Avoid wetting the foliage by using a soaker hose.

4. Spray fungicides such as Triadimefon; Triforine, Thiophanate-methyl and Propiconazole as soon as powdery mildew appears on plants. Cover the tops and bottoms of all leaves with the fungicidal spray. Natural methods to prevent or eliminate powdery mildew should be exhausted before turning to fungicides.

Tips & Warnings

• Some home remedies using soap may be harmful to plants.

• Check insecticide and fungicide labels for cautions about sensitive plants. Contact your local Cooperative Extension Office with concerns about plants.

References

• Ohio State University: Fact Sheet - Sooty Molds on Trees and Shrubs
• Ohio State University: Fact Sheet -- Powdery Mildews on Ornamental Plants
• University of California-Davis: Aphids
• Ohio State University: Fact Sheet - Sooty Molds on Trees and Shrubs

Resources

• University of Florida: Crape Myrtle in Florida IFAS Extension