Cool Season Turf Outcompetes Underlying Bermudagrass For Water

This summer, ultradwarf bermudagrass greens struggled to recover from fall overseeding in the desert southwest.   Although not all courses that struggled to recover from winter overseeding experienced the same challenges, there was one issue that was common in poorly performing greens.  This update will offer suggestions to overcome this problem with proper management this winter.

When collecting soil moisture data at courses that experienced poor bermudagrass recovery this summer, it was apparent that in many cases, the localized thin areas contained lower volumetric water contents than the dense bermudagrass portions of the green.  During the winter, when evaporative demand is very low and superintendents manage water with frost delays in mind, it is not uncommon to see soil moisture levels fall in the 5-10% range (measured with the Fieldscout TDR 300 Soil Moisture Meter with the 3-inch probes).  At the same time, the overseeded turf does not commonly show any signs of stress.  In the photo, the tan colored bermudagrass is wilting at 5% soil moisture, but the adjacent overseeded ryegrass does not show any signs of stress, although it is growing in the same sand-based soil mix.  The take-home message is that although the overseeded turf may appear turgid, the underlying bermudagrass may be under water stress.  It is during this time where it is essential to monitor soil moisture and irrigate when levels drop below normal (the critical soil moisture level often varies from course to course and even from green to green, and with that in mind, each turf manager should establish a ‘critical’ range for his course).  It is likely that the freezing temperatures much of the desert southwest experienced early this year, plus inadequate soil moisture, led to the failure of many ultradwarf bermudagrass greens this summer.

In summary, do not underestimate the ability of the overseeded turf to compete with bermudagrass for water and nutrients.  During the winter, when it is common to go 7-14 days without overhead irrigation, monitor soil moisture regularly (daily if time permits) and schedule irrigation with the underlying bermuda in mind.  Lastly, it is worth noting that although turf loss was fairly common on ultradwarf greens that were overseeded this winter, golf courses that chose not to overseed did not experience turf loss and found that water management was much simpler in the absence of the cool-season turf.