Response of Bahiagrass Hybrids to Metsulfuron.

Bahiagrass biotypes were collected from 12 counties throughout the state of Georgia between July 3, 2012 and July 20, 2012. Approximately 12 bahiagrass biotypes were obtained from 4 locations within each county. Seedhead branch number was used to identify possible bahiagrass hybrid biotypes. Biotypes with seedhead branch numbers ranging from 2 to 8 were collected. Each biotype was excavated from the site and transplanted into the greenhouse in Athens, GA. One month later, each pot was destructively harvested and approximately 20 to 30 rhizome cuttings, 2.5 cm in length, were replanted into pots. Each transplanted rhizome was considered a distinct bahiagrass biotype. Biotypes were grown to maturity in the greenhouse (not all survived). Morphological data were collected from regenerated bahiagrass biotypes (n = 1002) between November 11, 2012 and December 9, 2012. Collected data included leaf width at leaf base (mm), leaf width midway to leaf apex (mm), leaf length (cm), ligule description (membranous, hairy, or absent), ligule length (mm), seedhead branch number, seedhead length (cm), and flowering culm length (cm). Thirty possible bahiagrass hybrids were selected to represent the vast differences in morphology: GAR2-2, GAR7-1, GAR10-1, GAJ7-8, GAJ12-6, GAL4-15, GAL9-33, GAL11-17, GASU2-6, GASU4-4, GASU4-5, GASU9-2, GASU11-1, GASU11-2, GASU11-6, GAC8-4, GAC12-6, GAC12-8, GALC9-10, GACL13-10, GACL14-4, GAG1-10, GAW1-4, GAW1-5, GAW4-4, GAB11-15, GACH5-2, GACLCH1-7, GACLCH1-11, and GALCH4-9. Pots from all thirty biotypes were divided into 24 segments, transplanted in 1 liter pots, and grown for 2 months in the greenhouse. Two trials were conducted simultaneously in separate greenhouses. Experiments were arranged in a randomized complete block design with four replications. Bahiagrass biotypes were mowed to a height of 7.6 cm 24 hrs before herbicide application. Herbicide treatments were applied on June 28, 2013 with a CO₂ backpack sprayer calibrated to deliver 375 L ha^-1 at 221 kPa and consisted of metsulfuron at 0.021 or 0.042 kg ai ha^-1. A non-treated check was included for comparison. Visual ratings of % bahiagrass control were recorded weekly on a scale of 0 (no control) to 100% (completely dead bahiagrass). Pots were destructively harvested 6 weeks after treatment (WAT) and fresh weights (g) of above-ground biomass were recorded. GACLCH1-7 (3.25 g biomass), GACLCH1-11 (2.75 g), and GACLCH4-9 (1.43 g) exhibited the greatest tolerance 6 WAT to applications of metsulfuron at 0.021 kg ai ha^-1. Genetic analysis revealed that these biotypes were all tetraploids, similar to ‘Argentine’ bahiagrass, which has previously shown tolerance to metsulfuron. However, a fourth tetraploid, GAL4-15, was completely controlled by metsulfuron at 0.021 kg ai ha^-1. Several diploid bahiagrass biotypes (GAR10-1, GAW1-4, GAW4-4, GAB11-5, GACL14-14, GAL11-11, GAG1-10, and GACH5-2) also exhibited tolerance (0.43 to 2 g biomass) to the low rate of metsulfuron 6 WAT. The tetraploids GAL4-15 and GACLCH4-9 exhibited tolerance (0.5 to 3 g biomass) to metsulfuron at 0.042 kg ai ha^-1, while the diploids GAB11-15, GACL14-14, GAL11-11, GAG1-10, and GACH5-2 exhibited similar tolerance (0.5 to 4.15 g biomass) 6 WAT.