A plastic tarp is required to help slow gas release from the soil. It will control a broad spectrum of weeds, including perennials. Applying methyl bromide in strip treatments under clear plastic that is then used as a mulch to encourage early spring growth has been used successfully. For best results, it should be applied to well tilled soil free of large clods that was moistened by rainfall or preirrigated 2 weeks previously in order to enhance germination of weed seeds.
Typical application is with a subsurface spray blade into premade beds.
After 7-14 days, the caps are removed and allowed to air before planting. It can be injected into the sprinkler irrigation system and applied through drip irrigation tubes placed under a plastic mulch. There have been numerous failures with metam, mostly because of improper soil preparations. The label requires a 14 day waiting period between treatment and planting a crop. A narrow spectrum herbicide, good for annual grasses and common purslane.