The past week has brought low temperatures to the eastern United States that have not been experienced in decades. This cold front described as a "polar vortex" has brought overnight lows in Moore County into the single digits. When we experience low temperatures like these we worry about injury to our Bermuda Grass. This low temperature injury is known as "winterkill" and it is different from "spring dead spot" which is caused by certain root fungi during the fall and spring. The severity of "spring dead spot" is influenced by winter weather while "winterkill" is totally the result of severe winter weather. In the upper transition zone (Kentucky,Virginia, Oklahoma) "winterkill" is reported as a once every five year occurrence. In the Sandhills of North Carolina it is seldom experienced. However our new "ultradwarf" Bermuda grass varieties are thought to be more susceptible to cold temperature injury and this is the first time we have seen temperatures this low since we began converting our bentgrass greens in the Carolinas to "ultradwarf" Bermuda. It should be noted that our traditional hybrid Bermuda grasees used in the fairways can suffer "winterkill" but they are thought to be hardier and less susceptible to injury than the "ultradwarf" bermuda grass used on our two new greens.
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| winterkill in a bermudagrass fairway |
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| spring dead spot in a bermudagrass fairway |
University research has been done on ways to protect "ultradwarf" Bermuda greens from "winterkill". The consensus recommendation is that our first line of defense is the placement of geotextile covers over the"ultradwarf" grass. There are numerous options available in different fabrics from different manufacturers. These covers are usually custom cut and sewn for each green. Greens in the shade and greens facing north are more susceptible to injury so sometimes these greens are covered when others are not. The rule of thumb for covering is you should cover when the weather forecast predicts lows of 25 degrees F or lower for two or more consecutive nights along with daily highs of less than 50 degrees F. For our two new Bermuda grass greens we bought covers manufactured in Canada and and sold under the trade name "Evergreen".
Historically, covering greens in the South to prevent winter injury dates back to the 1920's. As southern greenkeepers struggled to find turf for use on their greens they found common bermudagrass to be the only grass which would survive the summer. However getting that common Bermuda to survive the winter was difficult. These early greenkeepers would establish a winter green of poa annua, ryegrass, or redtop in front of their summer green and then cover the summer green with pine straw for the winter. (USGA Green Section Record Volume 1 No. 12 December 16,1921.)
Because of the intense cold we experienced here this week we decided to try an old practice and add a pine straw blanket on top of our geotextile covers. Other golf courses throughout the south have done this also. This was far easier for us than most golf courses since we only have two Bermuda greens. The process of placing covers on the greens for cold weather and removing these covers when it becomes warmer is labor intensive. For 18 greens the typical labor force is 4-6 people for 4-6 hours. Often it is windy because we are installing covers as a windy cold front moves in. At left is a picture showing our chipping green with its geotextile cover and pine straw being removed.
We do no not have any way of providing additional protection in these cold temperatures for our Bermuda fairways. We took steps in the fall to prepare the turf for winter. We limited nitrogen fertilizer applications, we applied potassium and we raised our height of cut. Factors which can contribute to fairway Bermuda injury in the winter are shade, traffic, poor drainage and moisture deficiency leading to winter dessication. We would like to think that we have done all that we can do to protect our turf for winter. As the turf comes out of dormancy this spring we will monitor our golf course and do everything we can to have healthy turf this spring.
