Bermudagrass “recovery” continues in summer and fall of 2014, but it’s not too early to begin thinking about 2015!
Mike Goatley, Extension Turfgrass Specialist, and Erik Ervin, Turfgrass Physiology, CSES Department, Virginia Tech; Shawn Askew, Turfgrass Weed Specialist and David McCall, Turfgrass Pathologist, PPWS Dept, Virginia Tech
The past 15 months have presented a challenge to both bermudagrass sports turf and golf turf managers alike because of the persistently cool weather of the past two summers (with the summer of 2013 distinguished by well above average rainfall and lots of clouds) and the winter of 2013-14 being one of the harshest in 25 years. The summer of 2014 has also been a very mild season with many days being more fall-like in temperatures both for daily highs and lows. All of these weather patterns present challenges to a warm-season grass such as bermudagrass and serve as reminders that we live in a transition zone state where growing just about any grass has its own problems.
However, does this mean one should abandon bermudagrass for these uses? When Mike Goatley was asked at a recent presentation “would you recommend Kentucky bluegrass, tall fescue or bermudagrass for athletic fields?” the answer was “yes”! We can grow any of them in Virginia but we should anticipate their problems and limitations because of our climate AND our expectations for turfgrass use. The Virginia Tech Turfgrass Team is still a very strong proponent of bermudagrass for athletic fields and golf fairways because there simply is not another grass available to us that produces as much canopy density and recuperative potential as bermudagrass for heavily trafficked turfs. However, let’s consider what we hopefully have learned/observed from the challenges of these past 15 months that can apply to trafficked bermudagrass turf for this fall and beyond:
- There were no absolute guarantees of survival, but the genetics of the improved “cold tolerant” bermudagrasses came to the forefront in Virginia during the winter of 2013-14. Varieties such as Latitude 36, Northbridge, and Patriot (all vegetative) and Riviera, Yukon, and Sovereign (typically seeded) all demonstrated their cold tolerance this past year. Was there damage to these grasses? Yes. For the first time in memory, there was significant loss of Patriot athletic fields in northern Virginia, but the level of turf loss was not consistent statewide and damage was not catastrophic in most locations (more on the possible contributing factors to turf losses in additional bullet point items below).
- Extreme cold without the insulating effects of snowcover was definitely a major factor in the scope of winter damage this past year. However, there are always other contributing factors at play. For the winter of 2013-14 there did not seem to be a consistent pattern where typical problem situations such as poorly drained soils, shade lines, or aspect led to increased winterkill; there were as many times as not where the grass survived on these typically problematic situations, and it performed poorly on drier, sunnier, western-facing slopes. One consistent contributor to dead or damaged bermudagrass turf does return year after year: intensive fall traffic. This was evidenced again on both athletic fields and golf courses. Anything that can be done to distribute traffic (rotate goals on soccer fields, move practice drills around for football, alter entrance and exit points into/out of fairways and green complexes) will greatly improve survival. Similarly, any mechanical cultural practices (coring, solid-tining etc.) that can be done to reduce compaction in these areas are beneficial. Schedule cultivation in these trafficked areas as best you can around play. However, probably the most important thing that can be done is to distribute the traffic around the site if at all possible.
- Turf blankets definitely enhanced winter survival characteristics of bermudagrass on athletic fields. There is certainly significant expense in their purchase and labor for their installation and removal, but if protection of the bermudagrass field is a priority, then we have no better way to improve our chances of surviving a difficult Virginia winter than by covering it with a blanket. The blankets not only offer protection for the bermudagrass, but can also be beneficial in enhancing ryegrass overseeding development as well. Is winter protection absolute with a cover? Unfortunately, no. But year after year the ‘spring cover line’ distinction between covered and uncovered turfs is very evident as to the value of the blanket in winter protection and accelerated spring greening. If properly stored, standard turf blankets should easily last 10 or more years in most situations, so their cost really isn’t prohibitive if one considers what the price of regrassing a field might be if it is lost to an extreme winter.
- Continue mowing regularly for the rest of the summer and keep blades sharp. Many will notice that bermudagrass mowing quality declines from mid-summer forward and a reason for this is a change in the plant’s morphology due to shorter day lengths. The grass starts to grow more ‘upright’ than ‘lateral’. Plant growth regulators such as trinexapac ethyl and trinexapac ethyl+flurprimidol can enhance mowing quality and reduce cutting requirements, as well as improve late season wear tolerance and overseeding grass establishment later this fall if the PGRs are used as part of a regular program (aka, a single application of the PGR is of very little benefit). Another strategy successfully employed with bermudagrass is to use the PGRs up until a few weeks before anticipated frost and allow the bermudagrass to ‘rebound’ one last time after the PGR applications cease. Keep in mind that different varieties of bermudagrass demonstrate different tolerances to the PGRs so be sure to pay attention to label recommendations and/or talk to your peers about their experiences with various rates of PGRs on their bermudagrasses.
- Don’t get greedy with your cutting height. One of the strengths of bermudagrass is its ability to perform and play so well at relatively low cutting heights (< 1 inch). However, don’t keep those heights where they CAN be kept going into dormancy, but instead, consider where they SHOULD be kept as the grass goes into winter dormancy in order for it to better withstand possible extreme weather conditions. Raising those heights 0.25 to 0.5 inches BEFORE the onset of dormancy can be the difference between living and dead turf.
- Have you got current soil test results? If you have not conducted a soil test for the past 3 years, it is time to do so once again. Soil test in mid-late summer so that you can adjust pH, P, and K levels prior to dormancy. The bermudagrass still has several weeks left to respond to lime and nutrient adjustments before winter arrives.
- Continue to feed the bermudagrass while it is actively growing. The updated Nutrient Management Standards and Criteria from the Virginia Department of Conservation and Recreation allows for up to 0.7 lb N per 1000 sq feet per growing month for water soluble N sources, and up to 1 lb N per 1000 sq feet per growing month for slowly available N sources (defined as any N source with ≥ 15% WIN or SAN).
- Overseeding with ryegrass, while a necessity for many situations because of the need for an actively growing, green playing surface for the spring season, definitely reduced bermudagrass recovery this spring. Many that enjoyed what was an outstanding overseeded playing surface in the spring of 2014 were dismayed to find that there was very little bermudagrass remaining underneath that ryegrass canopy when they finally got around to removing the cool-season grass with a chemical transition aid such as one of the sulfonylurea herbicides. We also are starting to see our first occurrences of resistance to sulfonylurea herbicides on area athletic fields (for example, annual bluegrass on sports fields in Culpeper, perennial ryegrass on Worsham Field at Virginia Tech), so be aware of this for the future if you have been on a regular SU-based ryegrass removal program.
- Pre-emergent herbicides for this fall on bermudagrass fields and fairways: would you or wouldn’t you? It makes sense that on your most heavily trafficked areas that almost all PRE herbicides we use in Virginia have concerns with turf recovery, and certainly with any potential need for reseeding or resprigging that might arise in 2015. The duration and completeness of weed control with one of the more recent PRE’s to enter the bermudagrass market, indaziflam (Specticle), is phenomenal, but its use seems best suited for lower trafficked golf turf situations and definitely not on heavily trafficked sports fields. If you are interested in using standard PRE control products (pendimethalin, dithiopyr, prodiamine, benefin, etc.) of the standard winter annual weed complex of annual bluegrass, henbit, and chickweed, fall PRE’s on non-overseeded bermuda fields typically must go out no later than the first week of September in the valley and ridge regions of Va, mid Sept. in central Va, and by Oct. 1 towards Tidewater. Given that this has been a cooler than average summer, those dates might be a little ‘late’ for treatments in 2014, so keep your eyes open to what is going on with fall weed germination in your thinner turf areas as these dates approach. Early POST treatments of the winter annual weed complex are always desirable as compared to combating the weeds next spring, and always keep in mind the possibility of using non-selective herbicides for POST control during winter dormancy periods on non-overseeded bermudagrass.
- Spring dead spot (SDS) is problematic on most bermudagrass playing surfaces. While cold tolerant varieties are often less prone to the disease, they are still susceptible and damage may be severe. However, developing and continuing proper cultural management strategies can reduce severity over time. Core aeration to alleviate compaction and improve drainage as site use permits. Judicious use of nitrogen during growing months will aid in recovery, and can potentially reduce the likelihood of disease after multiple seasons. Nitrogen source recommendations are based on the pathogen causing disease at each specific location. We are currently working on a geography-based model as a nitrogen source decision tool. Several DMI and QoI fungicides are known to suppress SDS, though application over multiple growing seasons are required for complete control. Tebuconazole is a cost effective fungicide with above-average activity, but is only available for use on golf courses. Several combination products with multiple active ingredients are available to all turf managers.