Sage is an attractive herb. The leaves of this perennial plant are used in recipes or to season meat, dressings and other foods. This sprawling herb can grow quite tall, reaching heights of more than 2 feet. The leaves of sage can be purple, green, variegated or even gold, depending on the variety. All varieties of sage can be bothered by several types of insect pests.
The sweetpotato whitefly (Bemisia tabaci) attacks more than just sweet potatoes, as its name implies. This small insect pest attacks more than 500 species of plants including sages, according to entomologists with the University of Hawaii. These pests pierce the leaves of the sage and suck the sap from them, causing the leaves to wither and drop, and the plant itself to wilt. Heavy infestations can cause the sage plant to die. In addition, these whiteflies excrete a sticky substance called honeydew, which attracts ants and fungal spores such as sooty mold. Finally, whiteflies can also carry plant diseases.
Spray the sage with an insecticide formulated to kill whiteflies. Make sure to apply the spray to the undersides of the leaves, where larvae are often found. Repeat applications may be needed. Rinse the leaves of the sage plant thoroughly before consuming them. Note that these particular types of whiteflies are somewhat difficult to control using chemical means, according to horticulturists with the University of Hawaii.
Red and Black Flat Mite
These mites (Brevipalpus phoenicis) typically attack the stems of the leaves and plant first, then move on to the leaves themselves, feeding on the plant's juices and causing the sage to eventually die. Early symptoms include leaf wilt, brown or deformed leaves, and the death of the middle or inner tissue of the leaves. The feeding leaves holes in the plant and kills the surrounding tissue, sometimes causing scabs or sunken, dead brown areas on the sage plant.
Flat mites are susceptible to insecticides and can be easily killed with chemical means. Heavy infestations may require a second application. They are also tropical insects and do not do well in cold climates. As with all insecticide use, wash the sage leaves thoroughly before using them in foods.
Greenhouse whiteflies (Trialeurodes vaporariorum) are similar to sweetpotato whiteflies in that they attack a large number of different types of plants, although they are smaller than their counterparts. These pests are found throughout the world and feed off of the sap of sage and other plants. Unlike the sweetpotato whitefly, however, damage is often not visible other than a general decline of the plant, or the residue of sticky honeydew.
Note that the greenhouse whitefly has unfortunately become resistant to several types of synthetic insecticides. For that reason, horticulturists with the University of Hawaii suggest using insecticidal soaps or oils to control this insect. Repeat applications of the soap or oil as needed, and wash the leaves thoroughly before consumption.