Freeze/Thaw Cycles & Damage to Poa annua
The golf course sustained a minor amount of winter injury to the turf as a result of crown hydration. Crown hydration injury affects Poa annua during periods of thaw/refreeze events. When discussing winter injury it is important to remember that Cutten Fields has a two grass system, Poa annua and Creeping Bentgrass; Poa Annua is significantly more susceptible to winter injury than Creeping Bentgrass.
The three injured greens: 6, 9, & 17 have varying amounts of damage. Deciding on the use of temporary greens is determined by amount of damage and the location of damage. The 9th green was closed for a week and is now open for play. Injury on the 17th green is recovering better than anticipated. Progress is continually monitored and evaluated for potential opening.
The following is a summary of the winter preparations Course & Grounds perform on the course and the conditions that possibly led to the damage. In addition, we are providing an outline of recovery procedures and some changes that we will explore moving forward to reduce the potential for future damage.
The 4 types of winter injury that can negatively affect Poa annua and turf health.
Anoxia occurs over extended periods of ice cover. The maximum length of time Poa annua can survive under ice coverage with limited oxygen is 30-45 days. Management strategies include removing water and snow from greens before the formation of ice. Remove ice prior to 30-days of coverage. Unfortunately, weather conditions do not always cooperate when attempting either of these methods.
Crown Hydration occurs in spring during snow or ice melt or during periods of warmer weather in the winter. This winter damage is the most common form of winter injury. Temperatures are warm enough to melt significant snow and ice causing the plant to break dormancy and hydrate its tissues, subsequently a sudden drop in temperature to below freezing can burst plant cells causing turf loss.
Desiccation occurs when turf is exposed to wind and cold conditions for prolonged periods of time. Freezing removes the moisture from plant cells resulting in damage to turf by drought. The frozen ground does not allow the plant to take up water to replace the water that is lost to the windy conditions. Management strategies include tarps and snow cover. This type of winter injury is less common in this region
Low Temperature- occurs when turf is directly exposed to extremely cold temperatures for an extended period 1without snow cover. This type of winter injury is less common in this region
The process of winter preparation
In preparation for winter, Course & Grounds install temporary drainage channels in the low spots that have historically given us problems (1, 3, 5, 8, and 12). We place heating coils in these trenches to allow staff to melt ice and drain water from the low spots if necessary. Permeable tarps are utilized only on greens that are most susceptible to desiccation from wind (2, 6, 9, PG). Perforated tarps are often used in the spring to raise soil temperatures or to protect greens from wind desiccation in the absence of snow cover in the winter. The remaining greens are not tarped because tarps can interfere and slow down the process of removing snow. If snow must be removed from a tarped green it can significantly shorten the life of the tarps leading to significant yearly costs replacing ripped tarps. Through the years Course & Grounds often removes snow prior to thaw/refreeze cycles in an attempt to avoid the possibility of ice encasement or crown hydration injury due to warming. Snow removal has been successful at times but, is not an infallible method for managing winter injury.
Conditions that led to the damage
The course experienced temperature oscillations with days above zero, followed by days below zero, throughout the winter. The temperature passed through zero a total of 6 times in January resulting in mixed precipitation types. Temperature fluctuations provided opportunity for thaw/refreeze cycles to occur. Prior to a major temperature swing where a high potential for snow to melt and re-freeze exists, Course & Grounds removes snow from the greens. This was performed 3 times this past winter: December 14th, January 23rd, and February 14th -16th. It is difficult to determine an exact time when damaged occurred, although we believe if it occurred in the first half of January. The graph below shows the temperature fluctuations in January that led to the Poa annua injury.
What caused the damage?
Repeated thaw/refreeze cycles causes ice to form in and around the plant ultimately leading to injury. The persistent presence of melt water or rain water this winter created dangerous conditions for the turf as the turf was periodically encased in ice potentially causing crown hydration.
What will be the process to recover from injury?
The plan to restore the injured turf will involve the aeration, seeding and topdressing of the affected areas while covering with permeable tarps and watering with warm water to increase soil temperatures to accelerate germination and recovery. Aeration and seeding took place on March 26th, 2018. Despite the cold April weather and the ice storm, we are pleased to report that we have already observed some successful germination in the aeration holes on April 25th, 2018. Using of covers during the recovery process requires that greens with injured turfgrass will be closed and temporary greens will be employed. Temporary greens and covers are necessary to have the most efficient recovery process. Research has shown removing the stress of traffic on greens results in a 30% faster recovery rate (as opposed to greens in play). Not all injured turf will require temporary greens. In situations where the damage is localized or scattered, the green will remain in-play throughout the recovery process. The in-play recovery process will implement plugging turf from the nursery and utilizing soluble fertilizers to accelerate growth, increase density and promote recovery.
What will we do to avoid and reduce future damage?
We may need to prepare to deal with a different concept of winter than we have known in this area in the past. Instead of continual snow cover and very cold temperatures, winter may involve cold temperatures and snow events alternating with heavy rain and extended periods of warm weather creating substantial amounts of water from the snow melt and rain to deal with. Protecting the turf from these alternating conditions could require some potential changes to the golf course and our winter preparations.
Surface drainage: we will examine altering the fronts of some of the greens to improve the flow of water off the green surface. Some of our greens pool water up as it moves across the surface, creating puddles which can then freeze in place.
Surrounds: the topography of greens complexes and some bunkers are such that the surrounding areas drain onto the green surface thereby adding water that can cause damage. We will begin to examine ways to re-direct melt water away from the surface to minimize the amount of water on the surface.
Promoting conditions favorable to Creeping Bentgrass : Both Poa annua and Creeping Bentgrass thrive under different conditions. By having good sunlight, good drainage properties and the ability to manage traffic all create a more suitable environment for bentgrass.
Growing environments and turf health: the majority of this work has been addressed. However, the problem sites will be re-evaluated to determine if the fall/winter shade issues on these surfaces can be further reduced. The increased sunlight gained as a result of improved sunlight will significantly expedite the recovery process, in addition will assist to increase our Creeping Bentgrass populations.