Contrary to the common assumption, the mid to late summer in Florida is not ideal for bermudagrass turf growth and maintaining premium quality putting green conditioning. Yes, hot weather is needed for sustained active bermudagrass growth, yet frequent and at times extremely heavy thunderstorm activity, typical of the summer rainy season, brings on a variety of additional problems. With the occurrence of almost daily thunderstorms, a moisture-saturated rootzone exists for extended periods of time and oxygen content is depleted. This results in the development of a weak and shallow root system, and the turf's tolerance to other environmental and mechanical stresses is greatly reduced.
Significantly reduced sunlight intensity, as a result of dense cloud cover, is another concern because photosynthesis and storage of carbohydrates is limited. Inevitably, during this time of the year we receive SOS calls and visit courses where problems with declining turf health and quality are being experienced. Problems can be especially pronounced at facilities with older Tifdwarf greens that contain a moderate to high percentage of off-type surface contamination.
Constant high humidity, warm temperatures and free surface moisture are also the ideal environmental conditions for outbreaks and rapid development of many fungal disease pathogens. While the bermudagrasses have better disease tolerance compared to most other species, when it is in a weakened condition due to intense environmental stress, its susceptibility is increased. A number of years ago, Dr. Monica Elliot, with the University of Florida, determined that Gaeumannomyces graminis var. graminis was the primary causal organism for Bermudagrass Decline (BGD) disease. Other fungi were also found and the complex is oftentimes lumped together and described as ectotrophic root infecting fungi (ETRI). These fungi are always present, but it can be debated as to whether they are a primary problem or a secondary concern, the consequence of a weak and more susceptible host. The fact that no fungicide treatments provide curative control of Bermudagrass Decline just adds fuel to the fire with regard to this debate.
Research conducted by Dr. Bruce Martin, at Clemson University, and others has found that preventative fungicide treatments in the mid to late spring can help minimize overseeding transition difficulties as well as maintain improved bermudagrass health and quality in the summer. However, it has been my experience over the years that adjustments in other management practices are needed to minimize the occurrence of and recovery from declining bermudagrass or BGD.
Raising the height of cut of bermudagrass putting greens prior to the onset of environmental stress conditions is one of the key adjustments. Increasing leaf surface area is needed to compensate for reduced sunlight intensity. With Tifdwarf putting greens, it is recommended to maintain a height of cut in the range of 0.160 to 0.180-inch. While the ultradwarf bermudagrass cultivars such as Champion, Mini-Verde and TifEagle can tolerate extremely low heights of cut, it is still advisable to come up to at least 0.125-inch or slightly higher during the summer stress period.
Naturally, with maintaining a higher height of cut, complaints about slow putting speeds will arise. Regular double cutting and/or rolling in combination with growth regulator treatments are measures that can be employed to maintain acceptable conditioning of a consistent, smooth true ball roll and a medium fast putting speed when hosting general play. For tournament play or special events, lower heights of cut can be practiced for a short period of time, but they should be raised back up as soon as the event has concluded.
Furthermore, although verticutting is an important basic management practice for managing thatch accumulation and grain, it also exerts significant mechanical stress on the turf. Aggressive verticutting during the mid to late summer can be especially damaging to areas of off-type surface contamination, and thus care needs to be exercised with regard to both the depth and frequency of verticutting. Brush or groomer attachments on putting green mowers are less stressful alternatives, but not a total substitute for verticutting. Also, increasing the frequency of light topdressing to an every 7- to 10-day interval is very helpful in maintaining an acceptable playing quality as well as providing a degree of protection to the base bermudagrass.
