The effects of sethoxydim, cloproxydim, and fluazifop on photosynthesis and growth of St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze `Floralawn'], bahiagrass (Paspalum notatum var. saurae Parodi `Pensacola'), and centipedegrass [Eremochloa ophiuroides (Munro.) Hack.] were evaluated to determine if photosynthesis could be used as a rapid, nondestructive measure of relative susceptibility. Field and greenhouse studies were conducted using infrared CO2 analysis to estimate photosynthesis. Under field conditions, St. Augustinegrass was susceptible to sethoxydim and fluazifop applications, as indicated by a 40% and 38% reduction in apparent photosynthesis, respectively. Bahiagrass incurred a respective 62% and 51% reduction in apparent photosynthesis from sethoxydim and fluazifop application. Growth of these species, as measured by foliage dry weight, was also inhibited by both herbicides. Centipedegrass growth was unaffected by sethoxydim, but was reduced 48% by fluazifop. Under greenhouse conditions, centipedegrass apparent photosynthesis was reduced by sethoxydim and cloproxydim (41% and 51%, respectively), while fluazifop caused a 71% reduction. Growth of centipedegrass was significantly reduced only by fluazifop (83%). These studies indicated that in vivo photosynthetic measurements may provide a sensitive, rapid, and nondestructive method for determining the susceptibility of turfgrasses to postemergence grass herbicides. chemical names used: 2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-l-one (sethoxydim); (E,E) -2-[1-[[(3-chloro-2-propenyl) oxy]imino]butyl] -5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-l-one (cloproxydim); and butyl ester of 2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]-propanoate(fluazifop).
Greenhouse studies were conducted at the Univ. of Florida to evaluate the effects of preemergence herbicides on St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] rooting. Metolachlor, atrazine, metolachlor + atrazine, isoxahen, pendimethalin, dithiopyr, and oxadiazon were applied to soil columns followed by placement of St. Augustinegrass sod on the treated soil. Root elongation and biomass were measured following application. Plants treated with dithiopyr and pendimethalin had no measurable root elongation and root biomass was severely (>70%) reduced at the study's conclusion (33 days). Root biomass was unaffected following isoxaben and oxadiazon treatments, but oxadiazon applied at 3.4 kg·ha-1 reduced root length by 50%. Atrazine at 2.2 kg·ha-1 and metolachlor + atrazine at 2.2 + 2.2 kg·ha-1, did not reduce root length in one study, while the remaining atrazine and metolachlor + atrazine treatments reduced cumulative root length and total root biomass 20% to 60%. Metolachlor at 2.2 kg·ha-1 reduced St. Augustinegrass root biomass by >70% in one of two studies. St. Augustinegrass root elongation rate was linear or quadratic in response to all treatments. However, the rate of root elongation was similar to the untreated control for plants treated with isoxaben or oxadiazon. Chemical names used: 6-chloro-N-ethyl-N'-(l-methylethyl)-1,3,5-triazine-2,4-diamine(atrazine);S,S-dimethyl2-(difluoromethyl)-4-(2-methylpropyl)-6-(t∼fluoromethyl)-3,5-pyridinecarbothioate (dithiopyr); N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxybenzamide (isoxaben); 2-chloro-N-(2-ethyl- 6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide (metolachlor); 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one (oxadiazon); N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine (pendimethalin).
Field trials were conducted in Gainesville, Fla., to determine the influence of nitrogen fertilization on the interference effect of purple or yellow nutsedge on the yield of fresh tomato. Nitrogen (N) rates of 50, 100, 150, 200, 250, 300, and 350 kg·ha–1 were applied broadcast to the soil. Before transplanting, 1-m-wide soil beds were covered with plastic and fumigated with methyl bromide to suppress the growth on undesired weeds. Nutsedge-free and purple or yellow nutsedge-infested tomato plots were separately established. `Solar Set' tomatoes were transplanted in the middle of the soil beds, 50 cm apart in a single row. In nutsedge-infested plots, weed densities known to cause significant yield reduction in tomato (100 purple nutsedge plants/m2 and 50 yellow nutsedge plants/m2) were uniformly established perforating the plastic and transplanting viable tubers in the perforations. Purple and yellow nutsedge tubers were transplanted the same day as tomatoes and were allowed to interfere during the whole crop season. Results indicate that N rates had a significant effect on tomato fruit yield in both nutsedge-free and nutsedge-infested treatments. The presence of either purple or yellow nutsedge significantly reduced the fruit yield of tomato at all N rates. As N rates increased, tomato fruit yield reduction caused by the interference of either nutsedge species also increased. When yellow nutsedge was allowed to interfere with tomato, fruit yield loss was as low as 18% at 50 kg N/ha and as high as 42% at 350 kg N/ha. In purple nutsedge-infested tomato, fruit yield reductions ranged from 10% at 50 kg N/ha to 27% at 350 kg N/ha. N effects on nutsedge-free and nutsedge-infested tomato yields were described by quadratic equations, with maximum tomato fruit yield values being reached between 200 and 250 kg N/ha in both nutsedge-free and nutsedge-infested treatments.