Although sage (Salvia officinalis) is an herb you probably recognize immediately, many garden pests are repelled by its scent. Sage leaves contain alkaloids and essential oils that many pests find unpalatable and some, such as the wooly apple aphid (Eriosoma lanigerum) find deadly. Slugs and snails will use the plant for cover, but rarely eat it. A perennial in U.S. Department of Agriculture plant hardiness zones 4 through 7, the few pests that are attracted to sage are easy to control.
Sucking pests have mouth parts that allow them to suck the juices from a plant's foliage and stems. Western flower thrips (Frankliniella occidentalis) burrow deep into the sage plant’s flower buds and unfurled leaves and may go undetected until the damage -- distorted, wilting buds and white-specked leaves -- becomes evident. Whiteflies are tiny and white and feed on the undersides of foliage. They damage the sage plant by reducing vigor. Two-spotted spider mites (Tetranychus urticae) feed on the leaves' cell contents -- destroying 12 to 24 cells each minute, notes Insecticide Resistance Action Committee. Symptoms of a two-spotted spider mite infestation include white speckles on the leaves, especially near the large veins. Aphids are tiny juice-sucking insects, most active when the weather is dry. They are usually white or green and you’ll find them clustered on tender new growth.
If the sage plant's leaves appear ripped, torn or chewed, suspect a chewing pest infestation. Although there aren't many of these types of pests attracted to sage, all it takes is one to strip it of its leaves. The culprit is usually some type of caterpillar. Check the plant in early evening, just as it begins to get dark. Turn the leaves over and inspect them closely, the caterpillars may be tiny and the same color as the leaves.
Western flower thrips can spread viral diseases that cause the sage to wilt and die. There is no cure for these diseases, so avoid them by preventing thrips infestations. Many sucking pests excrete a sticky substance called honeydew, which, in turn, attracts a black mold, known as sooty mold. The fungal bodies fall off once the pests that caused the honeydew are under control.
Pest Prevention and Control
Pests hide in weeds, so keep the sage garden free of weeds and remove weeds surrounding the garden. Avoid high-nitrogen fertilizers and use water from a hose to knock off any pests you find on the plant. Manage whiteflies with a ready-to-use insecticidal soap spray, applied to the foliage to the point of runoff. Ensure coverage to the undersides of the leaves. Because mites are attracted to dust, prevent spider mite infestations by using the hose to rinse the sage plant foliage. Use organic pre-mixed neem oil for heavy infestations of mites and aphids. Spray all surfaces of the sage’s foliage, stopping just before the product drips from the plant. Aphids can also be knocked off the sage plant with a blast of water from the hose and caterpillars should be handpicked from the plant and crushed or dropped in a bucket of soapy water.