Bob from Gladys, Va writes
Unfortunately, Johnson grass and Orchard grass are both perennial grasses. Therefore, we are unaware of any selective herbicide that would kill the Johnson grass and not harm the Orchard grass. In this instance we would recommend spot treating the Johnson grass with a non selective glyphosate herbicide such as Gly Pho-Sel Pro with 41% Glyphosate and reseeding. Please be sure to read the product label for complete use instructions before use.
Answer last updated on: 08/04/2015