Dr. Pete's Turf Tips
Peter H. Dernoeden, Ph.D. Professor Emeritus, University of Maryland
We seldom see winterkill in cool season grasses in the mid-Atlantic – although crown hydration (ice crystals in cells) in annual bluegrass (i.e., Poa) sometimes occurs. More rarely we deal with a phenomenon called anoxia (oxygen deprivation). By far, it is bermudagrass that is most vulnerable to damage from low temperature stresses. Indeed, it is not uncommon to see Poa growing well in winterkilled bermudagrass. The specific cause of winter injury, regardless of cool –or warm season grass, can be caused by direct low temperature stress [i.e., ice crystal formation between and within cells as well as denaturation of proteins and other important biochemicals); winter desiccation (i.e., dehydration) ;traffic; and winter diseases (e.g., Microdochium patch; Pythium snow blight; others). Subfreezing temperatures cause water to move out of cells-leading to desiccation (i.e., dehydration). In the arid west, windy conditions combined with subfreezing temperatures causes winter desiccation in cool-season grasses. Desiccation, however, is more of a problem in bermudagrass versus cool-season grasses in our region.
Understanding stems is key to understating mechanisms involved in winter damage. That is, if Mother Nature kills the stems, plants die and don’t recover. The key to understanding the physiological nature of winter damage begins with a description of “The Crown.” The crown is the growing point of all grasses [aka apical meristem]. The crown is comprised of a mass of compressed tissues that are capable of rapid cell division [meristematic activity]. It all begins with germination of a seed. The first structures to emerge from the seed are a rudimentary root system called a radicle and a green shoot called a coleoptile. From within the coleoptile, the first true-leaf emerges, but thereafter leaves emerge within the confines of new sheaths. Leaves constantly emerge within individual sheaths (in good growing weather) in the configuration of a collapsing telescope.
Green leaves produce sugars (via photosynthesis) which “feed” the growing point –or crown. The crown is white and initially is tiny (the size of a pinhead). As previously noted, the stem contains compact masses of cells that divide rapidly to produce more and more shoots (i.e., leaves within sheaths), as well as roots and lateral stems called stolons and rhizomes. Each shoot or tiller is a combination of leaves telescoping within sheaths; each shoot/tiller has an individual crown or growing point (i.e., or meristem). The crown elongates as more shoots are produced. Photo 1 shows the elongated, white tissues of an annual bluegrass crown as well as roots at the base of the crown. The protuberances are axillary buds [growing stems], which can develop into new shoots/tillers (telescoping leaves in sheaths = shoots), roots and /or lateral stems (stolons and rhizomes). Tillering promotes density. In spring, in the absence of mowing, the crown elongates to produce a seedhead on top of a stem called the culm.
Elongated annual bluegrass crown with basal roots and protuberances, which will develop into new stems and shoots. After J.B. Beard, 1973.
In the case of Kentucky bluegrass, an axillary buds can develop into underground “lateral” stem called’ a rhizomes’. In the case of creeping bentgrass, axillary buds can produce above ground crawling ‘lateral” stems called ‘stolons’. And, in the case of bermudagrass, axillary buds can produce both rhizomes and stolons. Grasses like annual bluegrass (i.e., Poa), perennial ryegrass and tall fescue do not produce any lateral stems like rhizomes (rarely in tall fescue) or stolons. The aforementioned grasses are referred to as” bunch grasses” because they produce no lateral stems and spread by means of tillering.
Crown Hydration in Poa: When it comes to winter damage to turfgrasses –the action occurs in the crowns. Among cool-season grasses, annual bluegrass [Poa annua (Poa)] and perennial ryegrass are especially prone to low temperature stress damage. The scenario involves periods of freezing and thawing, usually during the mid-to-late winter to early spring period. During the thaw period, water enters the crown [water moves on a gradient from wet soils to into drier crowns]. At first, water builds-up between cells called intracellular spaces. When temperatures plummet to freeze wet surfaces, ice crystals form between and within (intercellular) the cells of crowns. Ice crystals act like tiny spikes that break membranes and even cell walls. The result is loss of cell integrity and a water-soaking of stem bases –the crown- and then total disruption of cell function. Poa is most commonly impacted. The first visual symptom is a vivid yellow or orange-yellow color in leaves and sheaths; eventually plants turn tan-brown and water-soaked, collapse and die. Surrounding creeping bentgrass normally is unaffected in our region.
Ice crystals between and within cells are the cause of crown hydration. Fry and Huang, 2004.
Distinct yellow-orange color of annual blugrass killed by crown hydration. Green grass is creeping bentgrass. Courtesy of D. Bevard, USGA.
Direct kill of Poa due to crown invasion by Pythium snow blight. The yellow-orange color is typical of crown hydration in Poa. Courtesy of J. Kaminski, PSU.
Crown hydration in Poa -bent unaffected. Note orange color due to crown hydration in Poa in foreground Courtesy of Darin Bevard, USGA.
Freezing and thawing predisoses Poa to crown hydration; get water away from greens.
Anoxia and Ice Encasement: is another form of low temperature direct kill, which only occurs when there is ice cover (i.e., ice encasement). Ice storms and encasement are uncommon in the mid-Atlantic. In deep snow, however, thaws can allow water to percolate down to the surface only to turn to surface ice when temperatures plummet. Ice layers lock out oxygen. The result is a build-up of carbon dioxide (CO2)–which directly kills plants. Other harmful substances like inorganics and alcohols are produced, which also are lethal. Anoxia [oxygen deprivation] is more common in more northern regions. Indeed. Montreal Canada is often subjected to ice storms and resulting ice encasement. Keeping Poa alive on greens in winter is one of the great challenges for many Canadian greenkeepers.
Background fairway encased in ice. The turf was perennial ryegrass and it was totally killed. Cicra 1980's Rockville,MD.
Anoxia in A-4 creeping bentrass in Sweden. Courtesy of B. Britton, CGCS.
Anoxia Management: The tell-tail sign of anoxia-is the distinct smell of rotten eggs or dirty socks-caused by methane gas. The odor often is referred to as the “smell of death.” Death of turf is non-uniform; it can be localized to a low area or encompass large areas. Poa is most susceptible to anoxia, which occurs within 60 days of ice encasement; whereas, creeping bentgrass and other cool-season-grasses may survive 150 days of ice coverage [in growth chamber studies ; Beard, 2002]. As noted below, anoxia actually can actually occur within 30 and 60 days in ice covered annual bluegrass and creeping bentgrass, respectively. There is no good solution to ice encasement. It helps to remove any snow cover and to spread black sand or charcoal to encourage more rapid melt of underlying ice. Attempts to remove ice lead to the proverbial “damn if you do and damn if you don’t. “Drilling, pitchforking or otherwise breaking of ice causes allows oxygen to infiltrate. However, upheaval of living turf in response to mechanical measures can lead to rapid turf death. See below for more information.
Anoxia damage in A-4 creeping bentgrass in Sweden. Courtesy of B. Britton, CGCS.
Anoxia in A-4 creeping bentrass in Sweden. Courtesy of B. Britton, CGCS.
Views From Barry Britton CGCS*; A Greenkeeper’s Experiences in Austria and Sweden: When writing this article, I contacted a good friend and Greenkeeper in Austria for his opinions in what to do in an ice encasement situation. The following information was provided by Mr. Britton, who has observed anoxia in annual bluegrass and creeping bentgrass developing at 30 and 60 days of ice encasement, respectively. The first telltale sign of an ice problem is ice depth and texture; clear and/or black ice are indicators of a developing anoxia problem. When ice is broken there is the smell of “dirty-sweaty” socks (methane). Barry is a firm believer in removing the ice from greens ASAP. At this juncture, it is time to inform the greens committee and membership that ice will be broken and that the effort is highly risky. If not done properly, ice removal can result in large losses of turf on greens. According to Barry, everyone needs to be in the loop, and it helps if neighboring golf courses are in the same situation. First step is to remove snow, and then topdress underlying ice-covered greens with either black sand, charcoal or pelleted poultry fertilizer. Barry, however, has no problem in getting aggressive with using a vertidrain set to shatter the ice. The key is not to go so deep as to penetrate the turf canopy. The objective is to crack ice to create air spaces for gas exchange, without disturbing the turf canopy or underlying soil. After cracking, the ice needs to be removed from greens with shovels. Equally important, is to squeegee off any surface water following ice removal and subsequent snow melt(s). If surface water is not removed, it will freeze at night and lead to crown hydration and possibly anoxia. While it sounds counter intuitive, it can be helpful to blow snow back onto greens, since snow is a good insulator. The three key points are: remove the ice from greens; eliminate surface water (via squeegee) and insulate with snow or covers. You must eliminate surface water during snow melt. If surface water is allowed to re-freeze a multitude of crown hydration and/or anoxia problems may be allowed to recur.
Remove snow cover ASAP and spread black sand or poultry pellets over iced areas . Sweden. Courtesy of B. Britton, CGCS.
*Barry Britton received his degree in Turfgrass Management from Guelph University in Ontario Canada. Mr. Britton rose to Master Superintendent, and Certified Golf Course Supt. He moved to Austria where is served as Director of Golf and Sports at Fontana Golf Club from 2001 to 2007. He then moved on to Director of Golf and Sports from 2007 to 2010 at Bro Hof G.C. in Sweden. Since 2011, he served as Golf Course Agronomist and Consultant in Europe. I thank him for his friendship and valuable insights used in the preparation of this article.
Barry Britton, CGCS; friend and agronomic consultant to golf
References:
Beard, J.B. 1973. Turfgrass: Science and Culture. Prentice Hall, NJ.
Beard, J.B. 2002. Turf Management for Golf Courses. Ann Arbor Press, MI.
Fry. and B. Huang.2004. Applied Turfgrass Science and Physiology. John Wiley & Sons, NJ.