Data on the efficacy of alternative fumigants to methyl bromide for weed control in perennial crop nurseries in California are needed because few herbicides are registered for this purpose. Field studies were conducted from 2003 to 2006 in four commercial perennial crop nurseries in California. Treatments included a nonfumigated control; methyl bromide (98%) (MeBr) with high-density polyethylene (HDPE) film; iodomethane (50%) chloropicrin (50%) with HDPE film; 1,3-dichloropropene (1,3-D) with HDPE film; 1,3-D (61%) chloropicrin (35%) with HDPE film; 1,3-D (62%) chloropicrin (35%) subsurface drip; and 1,3-D (61%) chloropicrin (35%) with virtually impermeable film (VIF). All the fumigants reduced the seed viability of common purslane, johnsongrass, and tall morningglory but were not as effective on little mallow and field bindweed. Although total weed densities and the level of control provided by each fumigant differed between locations, weed density was generally reduced by all the fumigation treatments, compared to the nonfumigated control. At three locations, alternative fumigation treatments usually resulted in hand-weeding time similar to MeBr. Reductions in weed seed viability, weed emergence, and weed densities suggest that these alternative fumigants will provide weed control similar to MeBr in perennial nurseries.
Nomenclature: 1,3-dichloropropene, chloropicrin (trichloronitromethane), iodomethane, methyl bromide, common purslane, Portulaca oleracea L. POROL, field bindweed, Convolvulus arvensis L. CONAR, little mallow, Malva parviflora L. MALPA, johnsongrass, Sorghum halepense (L.) Pers. SORHA, tall morningglory, Ipomoea purpurea (L.) Roth PHBPU