By Devendra Prasad Chalise and Emily (Merewitz) Holm, Michigan State University
Winterkill from ice encasement is a significant challenge for turfgrass managers in northern regions. The reasons why some turf species are more resistant to winter than others are still not fully understood. For example, creeping bentgrass can survive much longer under ice than annual bluegrass and perennial ryegrass. As part of the WinterTurf project, specific physical and metabolic traits are being investigated to determine what gives some grasses the edge in survival.
One potential factor is the plant's cuticle, a waxy layer covering the outer surface of above ground plant structures such as leaves and crowns - the plant's built-in raincoat. This wax layer is known to protect the plant from pests, diseases, light, and water loss in all seasons, but little research has been done on how the cuticle responds to ice encasement. We hypothesized that the longer annual bluegrass plants are encased in ice, the more their waxy outer layer degrades, which could translate to internal cell damage like membrane damage and overall slower recovery in the spring. This damage could contribute to increased susceptibility to winter or spring stresses, diseases, and pests. So, we aimed to understand how ice duration affects the plant’s built-in protective coating and its ability to bounce back from winter stress.
To test this, a controlled-environment growth chamber study was conducted using annual bluegrass sod pieces collected from the field following natural cold acclimation. Plants were exposed to three different durations of ice encasement: 0 days (no ice), 40 days, and 60 days. After the treatments, plants were de-acclimated and moved to a greenhouse to observe their recovery and the thickness of the wax on their leaves and stems was measured.
Unsurprisingly, the plants that were under ice for longer periods suffered more damage and recovered much more slowly. After 10 days of recovery, the plants with no ice exposure were green and healthy, while the plants that had been under ice for 40 and 60 days showed winter damage (Fig. 1).
Green cover was measured during the recovery period and a clear effect of ice encasement duration on green cover was found. The plants with no ice exposure recovered the fastest and reached 80% green cover in about 30 days, while the plants subjected to 40 and 60 days of ice took much longer (Fig. 2A). Based on the changes in green cover per day, the 0-day plants had the highest recovery rate, whereas the 60-day plants recovered the slowest (Fig. 2B), showing that prolonged ice stress slows the plant’s ability to bounce back.
The results of cuticular wax content indicate that the duration of ice cover did influence wax content. The plants with no ice stress had the most wax, while the plants that endured 60 days of ice had the least wax (Fig. 3). This suggests that prolonged ice cover may degrade this protective waxy coating, leaving the plant more vulnerable. It is possible that this loss of cuticular wax could be related to spring susceptibility to some environmental stresses and management practices. A thicker cuticle at the start of winter could be crucial for a plant's ability to withstand ice and recover quickly in the spring. These preliminary results have warranted additional studies to more conclusively demonstrate that ice encasement specifically causes a loss of cuticle. A study exploring the effect on cuticles of plants subject to winter dormancy with or without ice encasement is currently being conducted.
These initial findings raise other important questions: is the wax layer being damaged by the ice itself? Can management practices prior to winter influence this wax layer? What happens to waxes during the plant’s natural cold acclimation period prior to winter? For the latter question, we have conducted a field study to investigate temporal changes in the wax layer on both annual bluegrass and creeping bentgrass during their cold acclimation phase (September to December). We are interested to see whether there is a difference in wax layer components or integrity in these turf species heading into winter as these results are analyzed.
Read more about this study in our recent publication: Chalise, D., and E. Merewitz. 2025. Leaf and crown cuticular wax responses in Annual bluegrass (Poa annua L.) plants exposed to ice encasement. J of Agronomy and Crop Science.