Comparison of Cold Deacclimation of Annual Bluegrass and Creeping Bentgrass.

Turfgrass freezing tolerance levels can be negatively impacted during winter months due to exposure to warming soil temperatures, which may lead to deacclimation and susceptibility to freezing injury. Some information in the literature suggests that annual bluegrass (Poa annua L.) and creeping bentgrass (Agrostis stolonifera L.) differ in their capacity to resist deacclimation during winter months, which may contribute to interspecific differences in winter injury potential. Therefore, the objectives of this research were to compare changes in freezing tolerance of annual bluegrass and creeping bentgrass in response to a combination of different temperature and duration treatments to simulate deacclimation events.  Plants of annual bluegrass and creeping bentgrass were first subjected to a cold acclimation period of 2°C for 14 d followed by a sub-zero acclimation period of -2°C for 14 d in a controlled-environment growth chamber.  Following sub-zero acclimation, plants were exposed to temperatures of 4, 8, or 12 °C for 1 or 5 d, for a total of 6 temperature-duration deacclimation treatments.  Freezing tolerance (estimated as lethal temperature for 50% kill, LT₅₀) was determined following each deacclimation treatment.  Overall, creeping bentgrass exhibited higher freezing tolerance (lower LT₅₀) in comparison to annual bluegrass.  In addition, a loss in freezing tolerance for annual bluegrass plants was detected at lower temperatures and within shorter durations in comparison to plants of creeping bentgrass.