Sugarcane cultivar response to glyphosate and trinexapac-ethyl ripeners in Louisiana.

Sugarcane ripening in Louisiana is necessary to ensure adequate sucrose levels in early-season harvested sugarcane. The response of nine sugarcane cultivar's yield components to glyphosate and trinexapac-ethyl ripeners was determined in field trials. Glyphosate (210 g ae ha-1) and trinexapac-ethyl (200 g ai ha-1) treatments failed to increase sucrose yields more than non-ripened sugarcane. Sugarcane ripened with glyphosate or trinexapac-ethyl increased theoretical recoverable sucrose (TRS) 4 to 12% more than non-ripened sugarcane in seven out of nine cultivars, but greater TRS values were counterpoised by lower sugarcane stalk weight. An unintentional consequence of reduced late-season vegetative growth may benefit growers by allowing them to harvest more sugarcane hectares to meet their daily load quota and exposes fewer hectares to a freeze event. The cultivars HoCP 00-950, Ho 09-804, and HoCP 09-840 were not responsive to glyphosate or trinexapac-ethyl ripeners and should not be treated. A delayed harvest from 28 to 49 days after treatment (DAT) coincided with greater TRS values and 17% more sucrose yield.

Confirmation of herbicide resistance mutations Trp574Leu, ΔG210, and EPSPS gene amplification and control of multiple herbicide-resistant Palmer amaranth (Amaranthus palmeri) with chlorimuron-ethyl, fomesafen, and glyphosate.

Herbicide-resistant weeds, especially Palmer amaranth (Amaranthus palmeri S. Watson), are problematic in row-crop producing areas of the United States. The objectives of this study were to determine if chlorimuron-ethyl, fomesafen, and glyphosate applied separately and in mixtures control A. palmeri and confirm the presence of various genotypes surviving two- and three-way herbicide mixtures. Fifteen percent of A. palmeri treated with the three-way herbicide mixture survived. Mixing fomesafen with chlorimuron-ethyl or fomesafen with glyphosate to create a two-way mixture reduced A. palmeri survival 22 to 24% and 60 to 62% more than glyphosate and chlorimuron-ethyl alone, respectively. Previously characterized mutations associated with A. palmeri survival to chlorimuron-ethyl, fomesafen, and glyphosate Trp574Leu, a missing glycine codon at position 210 of the PPX2L gene (ΔG210), and 5-enolpyruvylshikimate-3-phosphase synthase (EPSPS) gene amplification; respectively, were present in surviving plants. However, 37% of plants treated with chlorimuron-ethyl did not contain heterozygous or homozygous alleles for the Trp574Leu mutation, suggesting alternative genotypes contributed to plant survival. All surviving A. palmeri treated with fomesafen or glyphosate possessed genotypes previously documented to confer resistance. Indiana soybean [Glycine max (L.) Merr] fields infested with A. palmeri possessed diverse genotypes and herbicide surviving plants are likely to produce seed and spread if alternative control measures are not implemented.