At 14 d after treatment (DAT), glufosinate at 0.42 kg ai/ha controlled barnyardgrass and broadleaf signalgrass 85 and 86%, respectively. Antagonism occurred for barnyardgrass control with all mixtures of glufosinate at 0.42 kg/ha. At 14 DAT, no herbicide was superior to glufosinate at either rate when applied in mixture for the control of broadleaf signalgrass. Rice flatsedge control 7 DAT was 68 and 82% with glufosinate at 0.42 and 0.84 kg/ha alone, respectively. The addition of propanil and triclopyr enhanced rice flatsedge control over that with glufosinate alone at 0.42 or 0.84 kg/ha. At 7 DAT, all herbicide mixtures increased spreading dayflower control compared with a single treatment of glufosinate at 0.42 kg/ha. By 28 DAT, spreading dayflower control was less than 80% with all treatments. Rice injury was less than 15% with all treatments.
At 14 d after treatment (DAT), glufosinate-resistant CPRS PB-13 rice was injured with early- and late-season glufosinate applications in 1998 and 1999. At 35 DAT, injury was less than 5%. Glufosinate delayed CPRS PB-13 heading by 7 to 15 d and reduced plant height at harvest but did not affect grain moisture and yield compared with the nontreated CPRS PB-13. But yield was reduced compared with conventional Cypress. At 14 DAT, glufosinate-resistant BNGL HC-11/62 rice was injured with early- and late-season applications. Treated BNGL HC-11/62 reached 50% heading 3 to 5 d later than did the nontreated. An application of glufosinate reduced plant height and increased grain moisture compared with the nontreated. Rice treated at the three- to five-leaf, preboot, and boot timings resulted in reduced yields compared with the nontreated BNGL HC-11/62.
Effect of weed interference duration and weed-free period on glufosinate-resistant rice was evaluated in 1998 and 1999. Weed interference for more than 2 wk reduced plant height 12 wk after emergence compared with the season-long weed-free treatment. Grain yield loss of 1,090 to 4,880 kg/ha was observed when weeds were allowed to interfere with rice from 2 wk to season-long. The weed-free period study indicated that early control of weeds could sustain rice growth and yield potential. This research suggests that effective weed control from 1 to 6 wk after rice emergence is important in fields with high weed densities for maximizing yield potential of glufosinate-resistant rice.
Seeds were collected from field-grown glufosinate-resistant rice treated at various growth stages from the one-leaf through the boot stage with glufosinate at 0.84 kg ai/ha. The collected seeds were evaluated for 100-count seed weights, germination, and seedling vigor. Germination of the long-grain transformant CPRS PB-13 at five temperatures was unaffected by glufosinate treatment or temperature. At 14 d after initiation, germination of the medium-grain transformant BNGL HC-11/62 was reduced at 22 C when treated at the preboot timing. One hundred–count seed weights and seedling vigor were not affected for either glufosinate-resistant line.
Two field studies were conducted in 2004 and 2005 to evaluate the response of glyphosate-resistant ‘TV52R42’ and ‘TV52R14’ soybean to glyphosate at 0, 458, 916, 1,375, 1,833, or 2,749 g ae/ha applied at the R4 reproductive growth stage and at R4 followed by the same rates at R6. A single glyphosate application at the R4 stage did not injure soybean or cause reductions in soybean height, nodes per plant, branch pods, main stem pods, or yield, regardless of application rate. Likewise, sequential applications of glyphosate at the R4 followed by R6 growth stages resulted in no adverse effects on growth parameters or yield. Preliminary findings indicate excellent tolerance to glyphosate application at reproductive growth stages beyond the currently labeled R2 growth stage restriction in varieties evaluated. Research findings warrant evaluation of an expanded range of germplasm under a variety of environmental conditions and potential effects on seed quality for establishment of tolerance levels and potential herbicide label amendments.
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