Why Do My Leaves Have Shiny Sap Covering Them?

Identification

• Honeydew is a sugary liquid that has a sweet taste to ants and other insects. Plant leaves with honeydew may also have large numbers of feeding insects. Honeydew causes a shiny coating on any material on which it settles, including cars, leaves, fruit and lawn furniture. Certain types of insects produce this excrement after consuming large amounts of plant sap while feeding on plants. Aphids, whiteflies and scale insects are honeydew-producing insects.

Signs and Symptoms

• In addition to honeydew-coated leaves, plants infested with insects that produce the substance may have leaves that are stippled or flecked with specks of yellow. Once honeydew drops onto plant parts, black sooty mold develops and covers the leaves. While the effect is primarily cosmetic, heavy coatings of the mold may result in insufficient sunlight reaching the plant, the leaves of which will consequently turn yellow.

Cultural Control

• Controlling or eliminating pests that produce honeydew is the only way to reduce the shiny appearance on plant leaves. Spraying your infested plants or trees with brisk jets of water twice weekly may remove insects. When small numbers of insects are present, you may easily wipe them from plant leaves with a cotton ball soaked in rubbing alcohol. Do this two or three times a week for best results.

Chemical Control

• Honeydew-producing insects are often controlled by applications of chemical products. Insecticidal soaps and horticultural oils are also effective. Thoroughly coat plant leaves with these chemicals for best results, as they are contact insecticides. Certain plants are sensitive to oils and soaps, so be sure to test any product on a small portion of your plant before applying it to the entire plant. If plants show no visible signs of damage seven days after application, treat the entire plant. Repeat chemical applications as necessary.