The common garden sage, Salvia officianalis, is a small shrub of the large genus, Salvia, part of the mint family. There are different varieties of leaf color: purple, golden or tri-color, but the soft grey-green sage is the toughest and most pungent. All produce elegant spires of blue/lilac flowers, much loved by bees in early summer. Often used as a companion plant to brassicas to repel caterpillars, it, too, is prone to attack from pests.
The Care of Sage
Keeping your plant happy and robust will make it better able to withstand attack from bugs. Do not overwater. Sage is a native of the Mediterranean and thrives in full sun and dry conditions. Harvest the leaves around flowering time for the fullest flavor, and after flowering, prune hard to promote new growth and prevent the bush from becoming woody and out of shape. Be prepared to replace your sage after three or four years. You may find it has self-seeded itself, or you can take cuttings in the spring. A handful of bone meal dug in around the roots twice a year will keep it healthy, and you can pick a sprig for use whenever you want. Sage is suitable for containers in sunny locations. Use liquid feed once a month and check for good drainage. Most of the bugs that attack sage plants are easy to recognize and can be dispatched without using chemical pesticides -- never a good idea in a culinary plant.
Slugs and Caterpillars
Black "bugs" could be caterpillar "frass" or dung. Examine the leaves top and underside and pick off the caterpillars, shaking the leaves clean. Place them elsewhere, in a remote hedge or larger shrub to preserve the butterflies. As sage likes a dry, sunny environment and slugs like it cool and damp, they should not be too much of a problem. Putting wood ash or gritty sand in a ring around the plant will deter slugs without having to resort to slug pellets. Otherwise watch for their trails and lure them away with a saucer of beer to one side. They will slip in and die happy.
Aphids, Whitefly and Thrips
Aphids can quickly colonize a plant, causing an unsightly twisting of the leaves; whitefly can appear in huge numbers and fly up in a cloud when you disturb the plant; and thrips are much smaller, winged insects that bore holes in the leaves and suck out the juice. All of them need similar treatment. There are chemical sprays available, but they are not advisable as they can leave toxins in the leaves. They also kill off any natural predators, such as ladybirds, lacewings and hoverflies. Whitefly is resistant to chemical treatment anyway. Wash the insects off with a soapy solution of diluted dish soap and spray regularly to keep on top of the problem. Hang a bright yellow sticky strip nearby (available at garden centers or you could make your own with card and honey). If all else fails, try an organic pesticide like pyrethrum or neem oil and keep a patch of nettles in your garden to attract ladybirds, which can then be moved onto your sage plant.
Spittlebugs and Spider Mites
Sometimes called froghoppers because of their froglike faces, you will know if you have spittlebugs by the blobs of "spittle" or white foam, which the females secrete from their rears and use as a protection from weather and predators. They do not cause a lot of damage, but the foam can be unsightly. Blast it off with water or insecticidal soap solution, making sure you dislodge the bug as well as its "spittle." Sage plants growing in conservatories may attract spider mites. These mites are microscopic, and you need a magnifying glass to see how they resemble tiny spiders. They live on the underside of older leaves, causing them to become discolored, depositing sticky, white strands of web. Remove and destroy damaged leaves, and wash the plant thoroughly with insecticidal soap. Phytoseilus persimilis is a natural predator for red spider mite. The name Salvia comes from the Latin "salveo" to heal, and your sage plant will soon recover from a bug attack with these simple remedies. Then it will be only you who are eating the leaves of your sage plant.