What Kind of Oil Spray Do I Use to Remove the Black on My Satsuma Tree Leaves?

Identification

• The leaves of satsuma trees infested with honeydew-producing insects often develop a black coating of fungus known as black or gray sooty mold. Honeydew is a sticky, clear liquid produced by insects after feeding on plant juices and sap. Once honeydew lands on satsuma leaves, sooty mold fungi sticks to it and causes a black, crusty fungus to appear. Sooty mold fungi grows only on the surface of leaves and fruit and is not harmful to the health of the tree, according to Ohio State University. Sooty molds can appear on any surface with honeydew deposits, such as sidewalks, cars and outdoor furniture. Often spraying the leaves with water will remove the mold. If that doesn't work, horticultural oils should do the trick.

Types

• Honeydew-producing insects such as aphids are common pests of citrus trees. These tiny pests produce honeydew after feeding. Aphids may or may not have wings and are light green, gray, light yellow, black or brown in color. Young seedlings suffer the most severe damage from aphid feeding and sooty mold often is seen near colonies of aphids on the underside of tree leaves. Other honeydew-producing insects also can infest satsuma tangerines, including whiteflies, scale insects and mealybugs.

Precautions

• Take precautions when applying horticultural oils to your satsuma tree. Since some plants and trees are sensitive to oil sprays, apply the product to a small portion of the tree before applying it all over. If no adverse effects are visible after seven days, it is safe to apply to the entire tree. Avoid applying oil sprays to your trees when temperatures are very high or very low. Freezing temperatures often cause uneven coverage of oil sprays, increasing the risk of injury to your tree. Apply horticultural oils when rain is not likely but humidity is high. Treating trees during the fall months increases the risk of winter injury, so avoid applying oils until winter hardening takes place. Horticultural oil sprays should not be applied within 30 days of insecticide treatments containing sulfur.

Solutions

• Horticultural oil sprays are made from refined petroleum products such as mineral oils. They often are effective in reducing the number of honeydew-producing insects on susceptible trees. Oil products work by placing an oily coating on the insect, which clogs its breathing holes and suffocates it. Once insects are under control, sooty mold disappears.