April 30, 2014

University of Arkansas, Division of Agriculture
Turfgrass Science Program (http://turf.uark.edu) – Turf Tips

Winterkill Observations - 2014

When we first came to Fayetteville in the late 1990s, we had several significant winters that led to widespread winterkill on bermudagrass golf courses and sports fields in the area. As we were trying to identify some research topics that were relevant for our area, winter injury became a focus of some of our early research at the UofA. From that research, we published several papers, gave lots of talks on winter injury, and learned a lot about selecting and managing grasses to improve winter survival. Since winterkill is not an every year occurrence, we subsequently had a decade of minimal winter injury and turfgrass managers (and researchers) tend to forget about such things when they don't come around as frequently as other common turfgrass problems. After this past winter and based on what we have seen this spring, it may be time to dust off some of those seminars, evaluate both old and new ideas, and revisit this topic that is always “chilling” just beneath the surface.

What have we seen so far? In the research plots, the story is genetics. The new NTEP bermudagrass and zoysiagrass trials were planted in Fayetteville last year and there are many cultivars and experimental varieties that are showing moderate to significant winter injury (Photo 1, Tables 1 and 2). Equally, there are many that have survived the winter without problems. If you have experienced winter injury and are looking to replant areas at your facility, we would certainly suggest you look carefully at this data and other NTEP datasets on winterkill before choosing a variety. Planting the same variety back into a microenvironment that is prone to winter injury will almost guarantee that you will have to address this problem again in the future.

One of our big questions coming out of this winter is the fate of ultradwarf bermudagrasses, as these cultivars continue to be planted farther north every year. There is one golf course in NW Arkansas with 9 ultradwarf greens (7 Champion and 2 Tifeagle) and, for the most part, they made it through the winter in good shape, as the superintendent raised the mowing height going into the winter and used turf covers regularly. However, even with those precautionary practices, two of his Champion greens had noticeable winterkill (Photo 2) and one had enough damage that some replanting will be necessary for repair. In our research plots, we saw significant damage on the ultradwarf plots and it appeared that Mini-Verde and Tifeagle fared a little better than Champion, which is similar to observations in years past.

Just about all the golf courses in the NW Arkansas area are showing some damage due to the severe winter, but most of that damage is localized to environments that are typically most susceptible to winter injury – north facing slopes, areas under low mowing heights, areas that areas that are shaded (Photos 3, 4, and 5) or experience more traffic, such as collars (Photo 6). The injury observed on the golf courses have covered a range of cultivars and have also extended from bermudagrass to zoysiagrass. What should you do if you have signifcant winter injury on your turf? The following paragraphs summarize our recommendations for dealing with winter injury.

If you are dealing with bermudagrass injury, you have several options, including waiting on recovery (assuming there is still some live plant material there), reseeding, or resodding. As has already been mentioned, if you need to replant, consider a cold-tolerant seeded bermudagrass like Riviera, or a cold-tolerant vegetative type like Northbridge, Latitude 36, or Patriot. Seeded types can only be used in areas where a pre-emergent herbicide has not been applied. If you are replacing sod and a pre-emergence herbicide was applied, be sure to cut the dead sod out as deep as possible to get beneath the herbicide layer. An application of activated charcoal can also be used to deactivate the herbicide and encourage rooting.

If you are dealing with zoysiagrass injury, the situation is a little more complex since zoysiagrass is such a slow-growing grass species that resodding does not necessarily get you back to good playing conditions right away. If you are seeing a lot of green shoots in a damaged area, it may be worthwhile to just let the turf slowly recover, as the existing surface, while not green, may be a better playing surface than a resodded area. If you choose to wait, you may want to consider using one of the new pigment or dye products to help mask the damaged areas during the recovery period. You will probably need to do a little testing at your facility to find that right concentration or mixture of dyes to match the existing turf. If you do decide to resod, just make sure that you give that sod ample time to root before allowing play on it and make sure your members and management are aware that it will take much of the growing season to heal the sod seams and get the turf back to a perfectly smooth surface again.

We hope this summary will not only help you to repair your winter injury and reduce the likelihood of future winter injury, but also make clear that this damage is widespread across NW Arkansas (as well as much of the the United States) and that you are not alone in dealing with the problem. Let's hope that the winter of 2013/2014 was a "once in a decade" event and that we won't have to re-visit this topic for awhile.

Good luck with the green-up,

Mike Richardson and Doug Karcher
Department of Horticulture
University of Arkansas

Bermudagrass winterkill varies among cultivars
Photo 1. Bermudagrass winterkill varies among cultivars. (Return to article).

Winter survival data among cultivars in the 2013 NTEP Bermudagrass Trial.  Fayetteville, AR.
Table 1. Winter survival data among cultivars in the 2013 NTEP Bermudagrass Trial. Fayetteville, AR. (Return to article).

Winter survival data among cultivars in the 2013 NTEP Zoysiagrass Trial.  Fayetteville, AR.
Table 2. Winter survival data among cultivars in the 2013 NTEP Zoysiagrass Trial. Fayetteville, AR. (Return to article).

Winterkill on ultradwarf bermudagrass putting greens.
Photo 2. Variable winter damage on ultradwarf putting greens in Northwes Arkansas.
(Return to article).

Winterkill on north-facing slopes
Photo 3. Increased bermudagrass winter injury on north-facing slopes. (Return to article). <

Zoysiagrass winter injury on north-facing slopes.
Photo 4. Increased zoysiagrass winter injury on north-facing slopes. (Return to article).

Winter injury on shaded zoysiagrass.
Photo 5. Increased zoysiagrass winter injury in a shaded area. (Return to article).

Collar re-establishment
Photo 6. Heavily damaged collars have been replaced with a cold- and traffic-tolerant bermudagrass. (Return to article).

Addendum - Observations from Little Rock

Following publication of this Turf Tip on April 29, 2014, it was requested that we add observations of turfgrass winter injury from Central Arkansas. Thank you to Dr. John Boyd for providing the following summary....

The winter of 2013-2014 caused significant damage to warm season lawns in central Arkansas. I have been a St. Augustine yard owner since 1987 and this is only the second time that I have seen this much damage to Little Rock lawns. For three consecutive nights in 1989-1990 the overnight lows ranged from minus 1° to 3°. My yard suffered almost no damage while my neighbor’s yard was 90% dead. This teaches you the unpredictability of freeze damage to plants. In December 2013, in Little Rock, there were 17 days when temperature reached 32° or less. January had 25 days of 32° or less while February had 18 days of 32° or less. On January 7th and 24th the lows were 9° and 11°, respectively. Damage to St. Augustinegrass and centipedegrass is very likely when temperatures drop to 10°. It does not always happen, but it did this year. Areas of my yard in full sun and with best stand of grass going into fall were hurt the most. Shaded and protected areas have almost completely recovered as of May 16, but other sections have a long way to go. I have no explanation for this phenomenon. Weak St. Augustinegrass resulted in more weeds due to less competition. Bermudagrass patches that were small for the last few years are expanding as I write. I made a second herbicide application to control new weeds in thin areas and applied 0.5 lbs of nitrogen per 1,000 sq ft using a 25-5-10 carrier. Your choices at this point are to be patient and wait for grow in or re-sod. Large patch seems to be a little worse in zoysiagrass in central Arkansas, perhaps because much of the zosyiagrass is struggling to get going.

Dr. John Boyd

Photo 7. Shaded St. Augustine lawn showing very little winter injury.

Photo 8. St. Augustine lawn in full sun showing significant winter inury and bermudagrass encroachment.

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