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Title: Direct-seeded watermelon herbicide study, 2002

Author
item SHREFLER, JAMES - OSU, WWAREC
item BRANDENBERGER, LYNN - OKLAHOMA STATE UNIV.
item Webber Iii, Charles

Submitted to: Oklahoma Agriculture Experiment Station Departmental Publication
Publication Type: Experiment Station
Publication Acceptance Date: 3/15/2003
Publication Date: 3/20/2003
Citation: Shrefler, J., Brandenberger, L., Webber III, C.L. 2003. Direct-seeded watermelon herbicide study, 2002. In: Brandenberger, L. and Wells, L. editors. 2002 Vegetable Weed Control Studies. Oklahoma State University, Division of Agricultural Sciences and Natural Resources, Department of Horticulture and Landscape Architecture. Stillwater, OK. MP-162. p. 42-46.

Interpretive Summary: Oklahoma watermelon producers currently have few good chemical options for controlling weeds. Broadleaf weeds are especially troublesome in that there are currently no approved postemergence herbicides. The objectives of this study were (1) to evaluate the efficacy and crop safety of Sandea (halosulfuron methyl), Strategy (premix of clomazone and ethalfluralin), additional approved herbicides, Spartan (sulfentrazone), and combinations of Sandea and other approved herbicides for preemergence application to direct-seeded watermelon and (2) to evaluate Sandea and Alanap (naptalam) for weed control efficacy and crop safety when applied postemergence. A field study was conducted during the 2002 growing season at Lane, OK on a Bernow fine sandy loam soil. Jubilee watermelon was seeded June 19, preemergence treatments applied on June 21, and postemergence applications on July 20 and August 3 to separate sets of plots. All preemergence treatments that included Sandea gave essentially complete control of carpetweed, tumble pigweed, eclipta and cutleaf groundcherry through August 6. Curbit (ethalfluralin) applied at 1.5 lb ai/acre gave a high degree of control of carpetweed and tumble pigweed, but significantly less control of eclipta and cutleaf groundcherry. The treatment combination of Alanap and Prefar gave good control of tumble pigweed, but not of the other weeds. Alanap applied alone at 3 lb ai/acre generally gave comparable or less control of the weed species evaluated than did the Alanap and Prefar combination. Spartan gave essentially complete control of all weed species at both rates. Applied postemergence, Sandea exhibited good weed control properties for the species evaluated. Crop safety was adequate in that, although there was crop stunting early in the season, stunted plants recovered and the low rate of Sandea resulted in the greatest yield of all treatments of the study. Strategy exhibited good crop safety, but was less effective than Sandea in controlling the weeds present. Spartan was very effective for control of the weeds on which evaluations were made, but also caused extreme damage to watermelon plants. Lower rates of Spartan should be evaluated to determine if a suitable weed control/crop safety window exists.

Technical Abstract: Oklahoma watermelon producers currently have few good chemical options for controlling weeds. Broadleaf weeds are especially troublesome in that there are currently no approved postemergence herbicides. The objectives of this study were (1) to evaluate the efficacy and crop safety of Sandea (halosulfuron methyl), Strategy (premix of clomazone and ethalfluralin), additional approved herbicides, Spartan (sulfentrazone), and combinations of Sandea and other approved herbicides for preemergence application to direct-seeded watermelon and (2) to evaluate Sandea and Alanap (naptalam) for weed control efficacy and crop safety when applied postemergence. A field study was conducted during the 2002 growing season at Lane, OK on a Bernow fine sandy loam soil. Jubilee watermelon was seeded June 19, preemergence treatments applied on June 21, and postemergence applications on July 20 and August 3 to separate sets of plots. All preemergence treatments that included Sandea gave essentially complete control of carpetweed (98.7 to 99%), tumble pigweed (98 to 99%), eclipta (99%), and cutleaf groundcherry (97 to99%) through August 6. Curbit (ethalfluralin) applied at 1.5 lb ai/acre gave a high degree of control of carpetweed (99%) and tumble pigweed (89.2 to 99%), but significantly less control of eclipta (5 and 45%) and cutleaf groundcherry (30 and 70%). The treatment combination of Alanap and Prefar gave good control of tumble pigweed (98.7 to 99%), but not of the other weeds. Alanap applied alone at 3 lb ai/acre generally gave comparable or less control of the weed species evaluated than did the Alanap and Prefar combination. Spartan gave essentially complete control (99%) of all weed species at both rates (0.2 and 0.4 lb ai/a). Applied postemergence, Sandea exhibited good weed control properties for the species evaluated. Sandea crop safety was adequate in that, although there was crop stunting early in the season (5 to 10%), stunted plants recovered and the low rate of Sandea applied preemergence resulted in the greatest yield of all treatments of the study (18,626 lb/acre). Strategy exhibited good crop safety, but was less effective than Sandea in controlling the weeds present. Spartan was very effective for control of the weeds on which evaluations were made, but also caused extreme damage to watermelon plants (52.5 to 97.5% stunting). Lower rates of Spartan, less than 0.2 lb ai/acre, should be evaluated to determine if a suitable weed control/crop safety window exists.