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88 GOLF COURSE MANAGEMENT 05.14 In case you didn't notice (and if you didn't, you must have been in a very isolated, very warm cave), it was a long, cold winter across most of the United States. This is not a good situation for people, dogs and turfgrass. So how bad is the winterkill going to be? It's been the topic of multiple tweets, seminars and Web chats. A recent article (published in Crop Science, 2014) by the brilliant minds at the University of Massachusetts (Lind - sey Hoffman, Michelle DaCosta and Scott Ebdon) determined effects of temperature on annual bluegrass and creeping bentgrass. Their research focused on two items: cold ac - climation, the process by which plants increase their freeze tolerance by exposure to low non- freezing temperatures ("cold hardening"), and, cold deacclimation, which is the loss of accli - mated cold hardiness. This deacclimation may occur in a warming trend. DaCosta's research group wanted to examine how sensitive annual bluegrass and bentgrass were to a brief warm - ing trend and how that warming could affect freezing tolerance. They took one annual bluegrass (a peren - nial biotype) and one creeping bentgrass (L- 93), and cold acclimatized those grasses. The plants received two weeks of 68 F (20 C) tem - peratures, followed by two weeks of 36 F (2 C) and then two weeks of 28 F (-2 C), with that last two weeks in the dark. At every two weeks in this process, they moved some of the plants to a growth chamber and then determined the soil temperature at which half the plants died. To do this, they lowered the temperature, little by little — 2 degrees at a time. Next, the researchers wanted to observe what happened if a brief warming spell oc - curred (the cold deacclimation). Plants were either left at 28 F, or they were warmed to 39 F (4 C), 46 F (8 C) or 54 F (12 C) for either one or fve days. After the one-day period, the re - searchers determined the temperature at which 50% of the plants died. They did the same for the plants grown at the new, warmer tempera - tures for fve days. What did they fnd? Well, frst, cold accli - mation worked. Both the annual bluegrass and bentgrass survived colder temperatures when they were acclimated all the way to 28 F. But, as it got colder, the annual bluegrass did not ac - climate as well as the creeping bentgrass. The bentgrass always survived colder air tempera - tures than did the annual bluegrass. What happened when it warmed up for a day or for a few days? Both grass species lost their freezing tolerance both as the soil tem - perature warmed, and as the number of warm days increased. Even one day of a 39 F warm - ing caused both grasses to have reduced freez- ing tolerance, as compared to the grass that was kept at 28 F. It was worse if the plants stayed at 39 F for fve days. The grasses were killed at even warmer temperatures if temperatures warmed up to 46 F for one or fve days (annual bluegrass and creeping bentgrass were killed at average temperatures of 13 F and 1 F, respec - tively). When it was even warmer — 54 F for fve days — the grasses were killed at a toasty warm temperature of 16 F. So, even a slight warming trend for a short period of time hurt the grasses' ability to tol - erate freezing. Perhaps more importantly, the annual bluegrass was far more affected than the bentgrass, with the annual bluegrass al - most always killed at lower temperatures than the bentgrass. So, annual bluegrass appears to be more sensitive to shifts in cold weather than bentgrass, and differences were observed even with a slight warming trend for a short period of time. This was a growth chamber study, and some of the temperatures at which 50% death was observed are pretty dang low. Snow cover, thatch and protective devices such as tarps will affect the winter survivability of annual blue - grass and creeping bentgrass. In addition, the sensitivity of annual bluegrass to deacclima - tion can vary depending on the biotype (as the researchers have observed in their follow- up studies). This study, however, clearly shows that if it warms a bit, even if only for a day, your annual bluegrass may be more sensitive than your creeping bentgrass. Source: Hoffman, L., M. DaCosta, and S. Ebdon. 2014. Examination of cold deacclimation sensitivity of annual bluegrass and creeping bentgrass. Crop Science 54:413- 420. For a longer version of this column, go to GCM 's blog (http://gcm.typepad.com). Beth Guertal, Ph.D. firstname.lastname@example.org Hey Poa, it's cold outside (verdure) Editor's note: This is the frst in a series of columns by Beth Guertal, professor in the department of agronomy and soils at Auburn University. The column is named "Verdure" for what Guertal calls the "best part of the grass, the green part that is left after you remove the clippings." Each Verdure column will offer a short synopsis of a research article published in a scientifc journal to answer a question frequently asked by superintendents. 088-089_May14_Verdure.indd 88 4/16/14 2:54 PM