Temperature and trinexapac-ethyl effects on bermudagrass growth, dormancy, and freezing tolerance

Applications of the plant growth regulator (PGR) trinexapac-ethyl [4-(cyciopropyl-α-hydroxymethylene)-3,5-dioxocyclohexane carboxylic acid ethylester] (TE) can delay winter dormancy in `Tifway' bermudagrass (Cynodon dactylon var. dactylon), which suggests a response to TE when temperatures are suboptimum for bermudagrass growth. The purpose of this study was to investigate the interactive role of temperature and TE in bermudagrass growth responses, dormancy, and freezing tolerance. Trinexapac-ethyl (0.11 kg a.i. [ha.sup.-1]) was applied in two growth chamber experiments, and across a 2-yr period in the field. Results indicated that TE reduced vertical shoot growth and increased stolon production, turf density, and quality when applied at high temperatures (35-36°C). While TE effectively reduced vertical shoot growth at low (20-22°C) temperatures, little impact on stolon development was observed under these conditions. Autumn applications of TE when temperatures were cool (≅ 25°C) at the time of application led to decreased turfgrass density and quality. These responses may explain the effectiveness of using TE to aid in bermudagrass transition to overseeded cool-season grasses and were probably due to the limited ability of bermudagrass to recover from initial post-application growth reduction and observed leaf chlorosis. Observed delayed autumn dormancy due to summer applications of TE and accelerated dormancy due to late-season applications did not conclusively relate to the freezing tolerance of bermudagrass.