Black or dark spots or patches, which appear suddenly on the lawn, may be the result of oil or gasoline spills from a leaking lawnmower or other gasoline-powered tools. Small gasoline leaks or spills volatilize quickly and no action is necessary. A severe oil leak or spill requires the removal of affected soil. Soil should be removed and replaced if it is saturated with oil or gasoline.
Time to consider eco-friendly lawn equipment
Replace gasoline-powered machines to reduce greenhouse emissions.
For small lawns - a reel-push manual mower.
Battery and electric-powered lawnmowers, trimmers, and edgers have improved and are worth investigating.