Determining Action Thresholds for Reducing Winter Injury of Annual Bluegrass Under Restricted Air-Flow Conditions.

Annual bluegrass (Poa annua L.) putting greens often experience winter damage due to several factors including anoxia, crown hydration, and freezing temperatures in the cold climates of North America. Previous research has shown a rapid loss of hardiness in annual bluegrass between 45 and 60 days (d) of continuous ice cover as well as a rapid depletion of carbohydrate reserves under anoxic conditions (Tompkins et al., 2004), but little is known about the relationship between ice cover, anoxia, and action thresholds for turf managers. The objectives of this study were to determine the effects of different gas concentrations on lethal temperature (LT₅₀) to establish action thresholds and the relationship between LT₅₀ and crown sucrose, fructose, and glucose contents in annual bluegrass. Annual bluegrass (Two-putt Poa annua cv. reptans) plugs (7.6 x 10.2 cm) were placed in hermetically sealed 1.9 L mason jars with the following gas treatments: air (20.9% O₂: 0.04% CO₂), slightly anoxic (5% O₂:10% CO₂), and anoxic (0% O₂:15% CO₂). Cold tolerance was evaluated at 15, 30, 45 and 60 d and LT₅₀ was determined.  Additionally, crown sucrose, fructose, and glucose contents will be determined and correlated with LT₅₀ data to examine the relationship between anoxia and crown carbohydrates. No difference in LT₅₀ was seen between the slightly anoxic (5 O₂: 10 CO₂) treatment and the air treatment, while the anoxic treatment (0 O₂:15 CO₂) had a reduced LT₅₀ value.  Cold hardiness was not affected by low (5%) O₂ conditions; however, once anoxic conditions are detected immediate action should be taken.