Mowing height changes and annual bluegrass putting green recovery from winter in field conditions or simulated ice encasement

Annual bluegrass (Poa annua) golf course putting greens are prone to winterkill in northern regions. Therefore, a 2-year field trial was conducted to investigate whether mowing height increases of annual bluegrass putting greens starting in late summer could improve winter recovery. Field plots in East Lansing, MI, were mown at a height of 3.17 mm (control), or the mowing height was raised gradually to a maximum height of 3.81, 4.44, and 5.08 mm. The changes in mowing regimes started in early September for both years. Normalized vegetative difference index (NDVI), leaf area index (LAI), and chlorophyll index (CHL) were measured during the fall and spring of 2021/2022 and 2022/2023. In March of both years, turfgrass plugs (10.16-cm diameter) were extracted from each plot and were transferred to a low-temperature growth chamber and encased in ice for 0 (no ice encasement), 10, 20, or 40 days. After ice encasement, percent green cover was determined and total nonstructural carbohydrate (TNC) analyzed for crowns, leaves, and roots. Fall NDVI, LAI, and CHL values were positively correlated with higher mowing heights, particularly 5.08 mm. Increasing duration of ice encasement reduced TNC in leaf, crown, and root tissues, but mowing height had no effect on TNC. Overall, increasing mowing height in fall may enhance annual bluegrass's spring recovery; however, additional research is needed to explore optimal mowing heights and timings.