Winter Of 2010: The Big Chill

Most of the Southeast Region experienced a prolonged period of temperatures 15 to 20 degrees below average during the first two weeks of January.  Many areas have not seen this duration of cold temperatures in decades.  Because many golf courses have converted from bentgrass to an ultradwarf bermudagrass, the topic of winter injury to bermudagrass putting greens has been much talked about.  In this article we will review what we have observed in the region and address some lingering questions.  

Observations

A standard recommendation in the region is to cover bermudagrass putting greens whenever temperatures are scheduled to fall below 25 degrees F.   The arrival of cold air was forecasted accurately, and courses with covers deployed them on January 1 or 2.   Temperatures fell to or below 25 degrees for almost 14 consecutive days (figure one).  In fact, this time span is the 8th coldest 14-day period in Birmingham since records have been kept.  Most courses kept the covers on for at least 12 or 13 consecutive nights.  The consistently cold temperatures kept the labor requirement to a minimum, as there was no need to put on and remove the covers each day.

As forecasted temperatures began to dip below 10o and the number of days with lows below 25o began to mount, superintendents contemplated extra protection.  Many courses in the Memphis, TN area used double covers for several days.  Another idea used successfully was to apply pine straw or wheat straw and then put the covers over the top.  This technique was helpful on shaded greens and putting greens with north-facing slopes.  The double cover and the straw-plus-a-cover methods effectively insulated the putting green regionalUpdateContentzone.   

Superintendents at several courses without access to protective covers decided to turn on the irrigation system in subfreezing temperatures to ice the putting greens.  Some superintendents froze a thin a layer of water over their covers.  We have no idea whether these techniques were effective, but they do raise some interesting discussion points.  

Lingering Questions and Comments:

1. We know that covers help retain heat in a putting green when deployed as described above.  Based upon research at Mississippi State University in the mid-1990’s, Dr. Mike Goatley observed that for temperature retention, there was not much difference among cover materials.  However, there was a larger benefit when two covers were used.  

2. Research in Canada in the mid-1990’s, and published in the September/October 2000 Green Section Record, “Winter Protection of Annual Bluegrass Greens,” confirmed that a straw layer underneath a cover provides improved protection. (/content/dam/usga/pdf/imported/course-care/000911.pdf ).  This research confirms regional field observations.

3. More questions than answers remain for icing the putting greens.  Theoretically, there is some potential for heat retention, but there is no research data to confirm or deny this concept.  Most courses that used this technique did so because they did not have covers and they used icing as a last resort.  We discussed the concept of icing with several turfgrass scientists who raised several questions, concerns, and comments:b. Is crown hydration a concern?  Crown hydration is not a good thing for any turfgrass that experiences cold temperatures.  If icing is used several days in a row, freezing and thawing can lead to crown hydration.  Crown hydration may be enhanced if the soil is frozen at the two-inch level and doesn’t thaw during the day.  The melting ice will have nowhere to go except for some surface drainage.  

a. Should an ice cover be used for one event (i.e. a single night) or for multiple nights in a row?  The influence of an ice cover on winter kill protection is difficult to determine because there are so many variables involved.

c. What is the best ice thickness for preventing injury?  Again, this is a difficult question to answer, and attempting to answer it brings in confounding questions about the temperature of the ambient air above the ice coating and how long the temperature stays below freezing.  

d. Because irrigation systems are not uniform, will there be likely be damage?    We do know that uniformity is variable and resulting ice coating will be variable, too.

As the calendar moves closer to March, we will know much more about any winter injury.  In the mean time, it would be a good idea for superintendents to take a few plugs from questionable greens and place them indoors in a sunny window.  In three or four days, you should know if you’ve got live grass.