Fumigant Alternatives for Methyl Bromide Prior to Turfgrass Establishment1

Potassium azide (PA) (112 kg/ha), oxadiazon + 1,3-dichloropropene (1,3-D) (168 kg/ha + 140 L/ha), dazomet (392 kg/ha), dazomet + chloropicrin (392 + 168 kg/ha), dazomet + 1,3-D (392 kg/ha + 140 L/ha), iodomethane (IM) (336 kg/ha), metam-sodium (MS) (748 L/ha), MS + chloropicrin (748 L/ha + 168 kg/ha), and MS + 1,3-D (748 + 140 L/ha) were evaluated at Jay and Arcadia, FL, in 1998 and 1999 as alternatives to methyl bromide (MeBr) fumigation for the management of common turfgrass weeds. Potassium azide was as effective as MeBr in controlling ‘Coastal’ bermudagrass, yellow and purple nutsedges, alexandergrass, broadleaf signalgrass, tall and sharppod morningglories, and various winter annual broadleaf weeds, but it failed to provide acceptable control of redroot pigweed. 1,3-Dichloropropene + oxadiazon did not control yellow nutsedge, purple nutsedge, or Coastal bermudagrass. Similarly, this combination treatment failed to control carpetweed but did provide 83% control of the winter annual weed species, 71% control of alexandergrass and broadleaf signalgrass, and ≥ 80% control of tall morningglory, sharppod morningglory, and redroot pigweed. Dazomet + combination treatments provided control of Coastal bermudagrass at Jay; however, control of common bermudagrass, alexandergrass, and broadleaf signalgrass was not acceptable at Arcadia. Sedge species control with dazomet + combinations was poor (< 63%) at both sites. Iodomethane, a treatment not yet registered by the U.S. Environmental Protection Agency (EPA), controlled weedy grass species, sedge species, and broadleaf weeds present at the two locations under different environmental conditions. Metam-sodium alone and MS + chloropicrin, tarped and untarped, and MS + 1,3-D provided acceptable weed control; however, MS + chloropicrin covered with a plastic tarp for 48 h was the best MS treatment. Metam-sodium + chloropicrin, with plastic tarp, controlled weedy grass and broadleaf species equal to MeBr; however, unacceptable sedge species control at Jay and Arcadia was 56 and 79%, respectively. Metam-sodium applied alone failed to control redroot pigweed; however, MS + combinations provided control. These studies confirm that no EPA-registered fumigant alternative to MeBr, applied alone or in combination for preplant turf soil fumigation, exists. Consequently, until such time that an effective alternative is identified, turf managers will be forced to forego fumigation, or they will have to choose a less-effective alternative and accept the consequences of contamination. Nomenclature: Chloropicrin (trichloronitromethane); dazomet; 1,3-dichloropropene; iodomethane; metam-sodium; methyl bromide; oxadiazon; potassium azide; alexandergrass, Brachiaria plantaginea (Link) A.S. Hitchc. #3 BRAPL; bermudagrass, Cynodon dactylon (L.) Pers. # CYNDA; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash # BRAPP; carpetweed, Mollugo verticillata L. # MOLVE; purple nutsedge, Cyperus rotundus # CYPRO; redroot pigweed, Amaranthus retroflexus L. # AMARE; sharppod morningglory, Ipomoea cordatotriloba Dennstedt # IPOTC; tall morningglory, Ipomoea purpurea L. # IPOPU; yellow nutsedge, Cyperus esculentus L. # CYPES. Additional index words: Fumigation, sod, turf. Abbreviations: 1,3-D, 1,3-dichloropropene; EPA, Environmental Protection Agency; IM, iodomethane; MeBr, methyl bromide; MITC, methyl isothiocyanate; MS, metam-sodium; PA, potassium azide; WAT, weeks after treatment.