Back Button
Table of Contents

Sooty Mold Treatment

Ellen Douglas
Table of Contents

Sooty mold is a fungal disease that can causes cosmetic damage to plants and sometimes stunts growth. It can be treated with basic measures.

Sooty mold is generally considered more unsightly than a serious killer of plants. In worst-case scenarios, however, the fungal disease can block out so much light that leaves can't take in the sun's rays to help them grow and stay healthy. Treat sooty mold by removing the insects that cause it, as well as the growth itself.

What to Look For

As its name suggests, sooty mold resembles a dark, ashy substance on foliage and woody growth. Look for leaves that are covered in a grayish growth or have large smudgy discolorations on them. Tree trunks and branches also show sooty mold as patchy spots.

Pest Carriers

Minor Infestation Treatment

Treating minor pest infestations can sometimes be all that's needed to nip the resulting sooty mold in the bud:

  • Dislodge aphids and other pest populations with a strong jet of water from your hose. Repeat this step every few days in the morning so that plants have a chance to dry off quickly.
  • Set up premixed ant bait stakes around vulnerable plants to help control the ant "farmers."
  • Prune away heavily infested branches and stems.

Major Infestation Treatment

A product such as neem oil can control both fungal spores and insect infestations. Typically, you mix 2 tablespoons of the oil for every 1 gallon of lukewarm water, but always check the label of your particular neem product.

A backpack sprayer or large spray bottle is your best bet for proving the kind of thorough coverage needed to apply neem to leaves and woody plant parts. Reapply every week or so while the problem persists.

Your first line of attack in combating sooty mold is to ward off the "bad guys" who are attracting the disease. Insects like aphids and whiteflies produce honeydew as they feed on, and excrete, bits of your plants. In turn, the honeydew attracts sooty mold fungal spores. As if that weren't bad enough, ants, which crave the honeydew, work to ward off beneficial insects that might otherwise eat the bad ones.

Homemade Help

A simple baking soda spray is often effective at preventing fungal spores from settling onto vulnerable plants. Mix about 1 teaspoon of baking soda into every 2 quarts of water, adding a drop of liquid soap to help the mixture adhere to the plants. Spray foliage once a week and after heavy rainfalls.

If prevention and treatment for mild infestations hasn't worked, there are a few things you can do to treat the foliage, trunks and branches of infested plants.

Treating Damaged Plants

  1. Prune away branches or stems that have heavily blackened or pest-infested foliage. Before and after using them, spray your pruners with household disinfectant or a diluted bleach solution to prevent the spread of sooty mold or any other disease.

  2. Spray the plants with water from a garden hose to dislodge existing sap-sucking pests.

  3. Add 2 to 3 teaspoons of mild, nondetergent liquid soap into a 2-gallon bucket of warm water, and blend the solution well.

  4. Using a soft-bristled brush, scrub foliage and woody plant parts to remove the dark growth from the coated leaves, trunks and branches.

  5. Repeat until you've scrubbed as much of the affected plant as you can. Empty and refill your bucket with soapy water as needed.

  6. Tip

    The insect known as scales also produces the honeydew that attracts sooty mold. As you're scrubbing your plants free of sooty mold, take advantage of the opportunity to remove these pests. Soapy water and a soft-bristled brush are an effective combination for scale removal.

  7. For information on powdery mildew, visit Powdery Mildew Treatment.