Ice Cover and The Role in Freezing Injury

It's been a somewhat crazy winter so far. Prior to Christmas to the first of the year we have had cold, snow and ice. Now we have warm wet weather with projected highs in the 60's for January 11, 2005 followed by temperature back in the 10's and 20's by the end of the week. Some of you may wonder what this is doing to the turf. I guess we will have to wait and see. I thought I would make a few comments regarding one part of winter injury, that being ice injury.

Intermittent ice formation on golf greens and fairways is a common event in Ohio and most of the northern United States. However, over the last few years ice formation has increasingly been singled out as the cause or strongly associated with winter injury. Ice injury can occur either directly from continuous ice cover or as part of freeze injury (low temperature kill).

Continuous Ice Cover Injury

The first type of ice injury is the direct result of a continuous ice cover. In the early to mid 1960's Jim Beard conducted controlled laboratory study where he looked at the survival rate of three cool season turfgrasses under a continuous ice cover and two turgrasses under field conditions (1,2). He found that creeping bentgrass could survive 120 days of continuous ice cover, however annual bluegrass (Poa annua) loss occurred after 60 days with substantial loss around 75 days. In a Canadian field study annual bluegrass and creeping bentgrass turf was subjected to 45 days of continuous ice cover and then the ice was removed. Seventy-five days after initiating the study and 30 days after removing the ice cover creeping bentgrass still maintained its cold hardiness, while annual bluegrass was dead (3). It would appear from this study that annual bluegrass under a continuous ice cover needs to be removed prior to 45 days.

The reasons commonly proposed for ice injury are the buildup of toxic gases and/or the development of anoxic conditions, and the loss of cold hardiness. It appears that carbon dioxide (CO2) accumulation under ice cover is a major contributor to the death of herbaceous plants (4). Intermittent thawing helped eliminate the CO2 buildup and injury to the plants in this study did not occur (4).

The loss of cold hardiness under ice cover occurs and varies among turfgrass species. Under continuous ice cover annual bluegrass loses its cold hardiness, while creeping bentgrass is not affected (3). The loss of cold hardiness in annual bluegrass is likely due to the anoxia (lack of oxygen) conditions that develop under an ice cover (3).

Although, ice injury to creeping bentgrass is remote, and certainly not an issue here in Ohio, I do wonder about its role in winter injury to creeping bentgrass on golf courses in the Rocky Mountains or Scandinavia where ice cover may exceed 120 days. It is not uncommon to observe creeping bentgrass greens that have suffered winter injury (photo to the left) believed to be caused by a combination of ice and freeze injury. It might be likely that prolonged anoxia conditions may reduce the cold hardiness of creeping bentgrass making it more susceptible to freeze injury.

Beard (5) reported differences among creeping bentgrass cultivars to ice cover. He found that seeded creeping bentgrasses, especially 'Seaside', are less tolerant of ice coverage than the vegetative cultivars like 'Toronto'. In addition, the colonial bentgrasses were considerably less tolerant than the creeping bentgrasses. Although published over 39 years ago - and the creeping bentgrass cultivars used may not be relevant at this time - the idea that variability among cultivars to ice coverage exists may make it difficult in extreme situations of ice cover to say "creeping bentgrass is not affected by ice covers".

Ice in Association with Freeze Injury

In Ohio and most of the Midwest and Northeast, a continuous ice cover exceeding 45 days is unlikely. The winter weather pattern is generally broken with intermittent periods of thawing that melts the ice. Where "ice injury" plays a more likely role is as a component of freeze injury. In this role the freezing of water that would occur with a rapid drop of temperature in or around the growing point during or after dehardening of annual bluegrass.

The critical precursor to freeze injury is the loss of cold hardiness through dehardening and subsequent rehydration of the annual bluegrass crown region. Continuous ice covers as previously mentioned contribute to the decline in cold hardiness. However, the most important factor regulating dehardening is temperature (6). In annual bluegrass the dehardening process can occur quickly when soil temperatures exceed 46 F (8C) for 48 hours (7).

What cultural practices can be instituted to minimize ice injury and/or freeze injury? A thorough discussion is found in the 2004 November/December issue of the USGA Green Section Record in an article entitled "Winter Damage" by Keith Happ, which is worth reading. A management program for reducing ice or freeze injury should center on:

1) Produce a healthy plant going into the winter. A weak annual bluegrass plant with low carbohydrate storage is not going to tolerate ice cover or be resistant to freeze injury as a healthy plant. Shaded areas are more prone to freeze injury than sunny areas, probably due to the carbohydrate status of annual bluegrass (8).

2) Eliminate poorly drained areas. Annual bluegrass growing in areas where water accumulates is at high risk to rapid freezing during freeze/thaw cycles.

In conclusion, winter injury is normally a combination of several factors one of which is ice cover. A continuous ice cover alone here in the Midwest is not a likely event. However, freeze/thaw cycles in late winter can create a situation where excessive water in and around annual bluegrass crowns can create freeze injury from the ice formed from the freezing of water.

References:

1. Beard, J.B. 1964. Effects of ice, snow and water covers on Kentucky bluegrass, annual bluegrass and creeping bentgrass. Crop Science 4: 638-640

2. Beard, J.B. 1965. Effects of ice covers in the field on two perennial grasses. Crop Science 5: 139-140.

3. Tompkins, D.K., J.B. Ross, and D. L. Moroz. 2004. Effect of ice cover on annual bluegrass and creeping bentgrass putting greens. Crop Science 44:2175-2179.

4. Freyman, S. and V.C. Brink. 1967. Nature of ice-sheet injury to alfalfa. Agronomy Journal 59:557-560.

5. Beard, J.B. 1966. Winter injury. Golf Superintendent 34(1): 24-30. 6. Tompkins, D.K., J.B. Ross, and D.L. Moroz. 2002. Dehardening of annual bluegrass and creeping bentgrass during late winter and early spring. Agronomy Journal 92:925-929.

7. Tompkins, D.K, C.J. Bubar, and J.B. Ross. 1996. Physiology of low temperature injury with an emphasis on crown hydration in Poa annua L. and Agrostis palustris. PTRC Report. web site: http://ptrc.oldscollege.ab.ca/researchreports.html

8. Rossi, F.S. 2003. New light on freeze stress. CUTT 14(3): 1,4

Authors: Karl Danneberger