Dilute liquid pre-emergent herbicide in a sprayer according to the amount indicated on the directions. Apply the herbicide in the shape of a circle or square around each grapevine or in a band down the row. Use a pre-emergent herbicide that contains active ingredients such as oryzalin, napropamide or oxyfluorfen. Apply in early spring before soil temperatures favor weed germination.
Spray grassy weeds with a post-emergent spray that contains sethoxydim, fluazifop or orclethodim. Direct the spray on grass foliage during a wind-free day. After a few days, dig up the dead weed foliage and discard.
Push a rototiller down the rows of the grapevines to break up perennial grass such as Bermuda or Johnson. Cultivations breaks up the rhizomes, or aboveground root systems, of perennial grass. You can rent a rototiller at a tool rental supply or gardening store.
Spray perennial grass in areas 4 to 5 feet away from grapevines, using a broad-spectrum herbicide containing glyphosate. Use on dry days to prevent herbicide runoff.
Spread a 3- to 4-inch layer of mulch 3 inches from the base of the grapevines out to 2 or 3 feet. Use organic mulch such as cereal straw, green waste or composted wood chips.