This is likely caused by leafhoppers. Leafhoppers are diminutive insects measuring less than one-tenth of an inch in length that attack the leaves of sage and other plants. Leafhoppers actually suck out the sap from leaves, which leaves pale spots that turn brown or bronze over time. Unlike caterpillars, leafhoppers don’t actually leaves holes in the plant’s leaves, just spots. The damage these pests cause initially appears as a collection of small white or yellowish spots that grow larger and merge together as the damage progresses. The leafhopper lays eggs inside the veins and petioles of plant leaves, making them extremely difficult to locate. The insect in the nymph stage has coloring similar to that in the adult stage. Nymph  leafhoppers are often found on the underside of leaves near a leaf vein; they are less active than adults and thus easier to spot. Adult specimens are agile and often jump from the plant when disturbed.

Fatty acid salts or insecticidal soaps can be a good choice against leafhoppers. They weaken the outer shell of leafhoppers but are safe to use on your plants and they don’t leave much of a residue which could kill beneficial bugs in your garden. With soaps, coverage is very important as it does not stay on your plant for long, so follow-up applications may be necessary.  Another option is Neem Oil. This will leave an unpleasant taste/smell on the leaves. There’s also some evidence Neem oil may be harmful to humans so use with care! That being said, Neem oil is an all-natural remedy that is very effective against many different types of bugs and mold, including leafhoppers. You will need a mister (also called a “One-Hand Pressure Sprayer”) to spray all the leaves evenly, since neem oil and water can separate easily.

Hope this helps!