Black mold, or sooty mold, is a common fungus found on a variety of plants throughout the United States. Insect infested fruit trees and fruit trees in close proximity to lindens and pines are most commonly affected. Although sooty molds are not particularly harmful, treatment may be necessary to preserve fruit.
Fruit trees affected by black mold are covered by a layer of fungus that appear like black soot from burning wood. The mold covering may be thin or thick but is superficial. Black soot can be scrapped with a fingernail to expose the plant underneath. According to the University of Wisconsin, all parts of a plant are affected.
Black mold is a dark fungi that grows on the honeydew left by sucking insects such as whiteflies, aphids, mealy bugs and and scale insects, reports the Broward County Florida website. The piercing sucker parts of the bug pierces the skin of the plant. The residue left from the digestive juices of the bug feeds the fungi.
Black mold is not a parasitic plant and will not kill the fruit tree, although it may prevent the proper development of fruit. Although rare, black soot can develop so thick on a tree that the mold blocks sunlight, according to Ohio State University. Fruit that is given reduced sunlight will have a reduced size and less color.
Preventing insect buildup on a fruit tree will reduce the incidence of black mold. Spraying a tree with water will remove build up of small insects and early signs of black mold.
Use a contact insecticide to reduce insect populations around the tree. Identify the insect on the tree by using an insect identification key from a local university extension, or by sending a sample of the insect to your local university extension for identification. Buy the correct insecticide to control the specific infestation. Products such as insecticidal soap, malathion or diazinon are effective. Systemic insecticides help when lots of honeydew is present on the tree.