We cannot clearly see the damage to the Russian Sage leaves. They tend not to be susceptible to insect feeding, though aphids, spider mites, whiteflies, and leafhoppers can occasionally do damage. We see no evidence of these insects or their feeding styles in the photo.

A generalist shiny black bug that can feed on foliage is Flea Beetle, though we cannot find records of them causing problems on Russian Sage. They can be controlled with pyrethrum, neem, or spinosad insecticides if damage is severe. A smaller, softer insect could be aphids, which can be very dark in color. Horticultural oil or insecticidal soap should be sufficient for their control, though often predators control them without the need for insecticides. Four-lined Plant Bugs can also have a wide host plant range, and their feeding can cause leaf lesions. https://extension.umd.edu/hgic/topics/plant-bugs

Malathion's information is listed at the bottom of this page, but its use should not be necessary: https://extension.umd.edu/hgic/topics/fruit-insecticides

In case any insects present are not causing this damage, several leaf-infecting fungi can affect Russian Sage, and this year's spring weather has been very conducive to the spread of fungal infections. Various leaf spots and stem blights can take hold, but should be able to be controlled by pruning out symptomatic areas, as fungicides are not curative.

Miri