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Sooty Mold

Sooty mold. Photo: B Bushe

Photo: Brian Bushe, CTAHR

Problem

Black, sooty growth on the leaves and branches of your trees.

Description

Sooty mold is a fungus that appears as a black, sooty growth on leaves, branches and, sometimes, fruits. It is non-parasitic and not particularly harmful to plants apart from being unsightly. Potentially, it could affect the plant’s ability to use the sun for photosynthesis. If you can rub the black growth off with your fingers, it is probably sooty mold. If you cannot rub it off, it is most likely something else.

Sooty mold on tomato. Photo: Dr. W Nishijima

Sooty mold on tomato
Photo: Dr. Wayne Nishijima

Information

Get rid of sooty mold on your plants by controlling the source. Sooty mold is created when aphids, whiteflies or scales infest the plant. Aphids feed on the leaves of the plant and secrete honeydew which attracts ants which then feed off of the excretion. The ants farm the aphids, moving them from place to place on the plant. Sooty mold develops on the excess honeydew. If you control the ants and eliminate the aphids (or other pests) the sooty mold problem will clear up.

Use soap and oil spray to control or eliminate aphids, scales and whiteflies. Use an approved insecticide to get rid of the ants. Ant bait must stay dry to be effective, so protect from rain.

You can wash sooty mold off a plant with dilute soapy water. Use cheap dish washing detergent, not the grease-busting kind as these will strip the wax off the leaves of the plants.

Soft Bodied Insect Spray Recipe:
(controls aphids, mealybugs, whiteflies, scales, citrus black flies) 

Begin by preparing a stock solution of Soap-Oil Concentrate:

  • Combine 1 Tablespoon of mild dishwashing liquid (Ivory, Joy or Dr. Bronner’s, NOT ultra formulas like Dawn) with
  • 1 Cup of vegetable oil (peanut, safflower, corn, soybean, sunflower oil)

How to use the Soap-Oil Concentrate:

  • Shake the solution of Soap-Oil Concentrate very well before use
  • Dilute with water by mixing 1-2 teaspoons of concentrate into 1 cup of tap water.
  • Spray plants thoroughly in the morning or late afternoon, especially the undersides of leaves
  • Spray once a week for 2 or 3 weeks to eliminate the insects.

Kendal Lyon, Hawaii Island Master Gardeners