Monitoring Seasonal CO2 Efflux of Dallisgrass and Bermudagrass: Implications for Non-Selective Weed Control.

Anecdotal observations suggest that dallisgrass and hybrid bermudagrass proceed into winter dormancy at different times and/or rates in certain environmental settings. Identification of a time frame when bermudagrass is dormant while dallisgrass is physiologically active would allow for the safe, yet efficacious application of a non-selective herbicide for dallisgrass control. Two separate studies were conducted during the Fall of 2015 to investigate the onset of dallisgrass and hybrid bermudagrass dormancy. Studies were conducted at the University of Georgia Golf Course in Athens, GA and Lane Creek Golf Club in Bishop, GA. Plant respiration was measured with a Li-Cor 8100 to determine the level of dallisgrass and hybrid bermudagrass activity at each golf course. A fixed cross-sectional area of 318 cm² was measured for each sample. Four samples (replications) of dallisgrass and hybrid bermudagrass were obtained at two separate locations (full sun) per golf course. Samples were also recorded on bare ground to account for background soil respiration. Respiration levels for each species were fitted against cooling degree days with a base temperature of 21°C using the formula CDD = 21 – [(T_max + T_min)/2]. Data were then fit to an exponential decay function (Respiration = a*e(-b*CDD)) using SigmaPlot. Results suggest that total respiration per sample area was different for each species at the initiation of the study. However, dallisgrass did exhibit a higher amount of net respiration (μmol m^-2 s^-1) throughout the duration of the study at both golf courses. This indicates that differential behavior concerning initiation and proceeding of dormancy may exist between dallisgrass and hybrid bermudagrass at the locations sampled. This may not be true when examining different microclimates on golf courses such as shaded or low lying areas. Further research and statistical analysis are needed to determine the significance of this phenomenon that occurs between these two species.