Viewing Lightweight Green Rolling as Part of a Season-Long Maintenance Practice

In 1901 Walter Travis wrote, “From May until October each green should be rolled daily with a light roller, rather than once or twice a week with a heavy one” .  For the next quarter century the debate over roller frequency and weight was waged in numerous publications.  However, due to a lack of research the issues were never resolved and the practice of frequent green rolling ceased as turfgrass managers began to understand the implications of soil compaction on turfgrass rooting.

       In the early 1990s the practice of green rolling was resurrected, attributed to the demand for fast green speeds.  With its resurrection came articles praising its use for tournament preparation while warning of negative implications if overused for regular play.  Superintendents searching the literature for advice regarding rollers found the cultural practice had rarely been researched.  Clearly, there was a need for research to investigate roller frequency and the potential for above ground turfgrass problems associated with continual season-long turf rolling.

       Identifying this need, a handful of turfgrass researchers initiated lightweight green rolling studies to maximize its benefits (primarily increased green speed) without introducing negatives (decreases in turf quality).  Unfortunately, for those that just read the abstracts or conclusions of papers, some of the results of these studies may appear contradictory.  The following article will consider the similarities and apparent discrepancies in lightweight green rolling research in an effort to clarify century old concerns regarding roller frequency and weight.

Frequency & Compaction

       Over the past decade three studies considered the impact of season-long green rolling on soil  compaction.  At Penn State University (PSU) both USGA and native soil plots were rolled 0, 1, and 2 times per week resulting in no change in turfgrass quality, soil bulk density, or water infiltration.  Michigan State University (MSU) rolled USGA and native soil bentgrass greens 0 and 3 times per week resulting n no significant change in turf quality, soil compaction, or water infiltration.  At North Carolina State University bentgrass greens were rolled 0, 1, 4 and 7 times per week.  Once again, plots rolled once per week resulted in no reduction in turfgrass quality.  However, rolling 4 and 7 times per week decreased turfgrass quality on both USGA and native soil greens.  Furthermore, compaction increased on the native soil greens rolled 4 and 7 times per week during the first year of the study.

             It is noteworthy that the decreases in quality attributed to lightweight rolling 4 and 7 times per week were not immediate.  The reduction in turfgrass quality at a frequency of 7 days per week took three to four weeks to manifest.

 Green Speed

       Most rolling studies have considered the immediate and residual effect rolling has on green speed.  All have concluded rolling noticeably increases green speed on the day rolling is applied.  The amount of increase ranged from day to day, attributed to other management or environmental factors, but in general rolled plots were approximately one foot faster than non-rolled plots on the day they were rolled.

       The residual effect that rolling has on green speed is not as clear-cut.  Several studies report a residual effect of up to 48 hours, while others report the increase lasts no more than one day.  A thorough investigation of the research indicates that there are four factors that account for this apparent discrepancy.  These factors are statistical significance, roller weight, roller type, and roller frequency.

      Statistical significance is the basis for the claim that the residual impact on green speed lasts up to 48 hours.  These claims are scientifically valid and attest to the meticulousness of the researchers and the precision of the Stimpmeter.  However, the 48 hour increases in speed are usually three inches or less.  Golfer surveys indicate that most golfers could not detect differences in green speed of six inches or less.  Thus, the three-inch difference is valid scientific reporting, but from a real-world aspect the greens would be noticeably slower two days after rolling to the golfer.

       Roller weight and type appear to be linked together.  It would seem logical to assume heavier rolling machines would result in greater increases in green speed for a longer period of time.  However, results from a study at MSU indicate roller type must be considered with roller weight.  In the study, a triplex attachment roller weighing approximately 1300 pounds and a sidewinder roller weighing about 950 pounds were included in the study.  Both increased green speed approximately one foot on the day they were applied compared to non-rolled plots.  However, the day after rolling the triplex rolled plots averaged three inches faster than the check while the sidewinder rolled plots averaged six inches faster than the check.

       Let’s further consider this six-inch residual green speed the day after rolling.  As previously mentioned most golfers cannot detect a difference in green speed of six inches or less.  Consequently, if a rolling treatment results in a one foot increase in green speed and only six inches of that are lost the next day, then the golfer would not be able to detect the difference in speed the day after rolling as compared to the day of rolling.

Roller frequency and duration (length of time adhering to the same roller schedule) apparently has an effect on residual green speed too.  This is most apparent when comparing mowing height green speed studies performed at Arizona State University (ASU) and MSU.  Both universities researched the premise that it may be possible to raise mowing heights and with the aid of rolling retain green speeds identical to lower heights of cuts that are not rolled.  The difference in mowing heights was identical (.03 inch), but the roller frequencies differed in that the ASU study rolled two times per week while the MSU study rolled three times per week.

       Results of the ASU experiment suggest that non-rolled, low-cut turf is faster than the rolled, high-cut bentgrass.  At MSU the non-rolled, low-cut turf plots were also initially quicker than the rolled high-cut plots.  However, after two weeks of rolling the high-cut plots retained the same green speed as the non-rolled, low-cut turf on the day of and the day after rolling treatments were applied.

 Additional Observations

       Golf course superintendents have been justifiably concerned that rolling may lead to diseased turf.  Dollar spot is a turfgrass disease spread primarily by maintenance equipment that carries the mycelium and infected plant tissue from green to green.  Given this mechanical form of spreading it is reasonable to assume rolling would increase the severity of this disease.  However, dollar spot severity decreased on MSU research greens rolled three times per week for five straight years.  It is hypothesized that these positive results were obtained because of the timing of the mowing and rolling.  Synonymous with most golf courses, the research greens were mowed at dawn and rolled within an hour after mowing.  This timing is believed to be important because early a.m. mowing may exacerbate the release of guttation droplets due to turgor pressure that remains at that time of day.  These guttation droplets are used as a nutrient supply by fungal pathogens.  Rolling after an early a.m. mowing may disperse concentrated guttation water, thus reducing the severity of disease symptoms.

       Debris (excess leaf tip clippings that miss the bucket) also adheres to the rollers and is transported back to the wash-pad.  This debris is not only a possible nutrient source for the pathogens, but may also contain black cutworm eggs.  In 1998 Dr. Potter from the University of Kentucky reported black cutworm moths lay nearly all their eggs on the tips of leaf blades and that many eggs survive passage through the mower blades and will later hatch (8).  On  a green rolling research site at MSU bird activity highly coincided with numerous black cutworms being observed on the site.  While no attempt was made to quantify the amount of cutworms on the site, significantly less bird beak intrusions were observed on greens that were rolled.  Considering debris adheres to green rollers and is transported to the wash-pad, it is conceivable that rolling could have decreased the amount of cutworms per green by removing eggs with the excess debris.  The only negative observed on plots rolled (under 4 times per week) compared to non-rolled plots is on one occasion MSU reported rolled plots displayed more Microdochium patch symptoms in the late spring than non-rolled plots.

 Conclusions

             After 100 years of dispute researchers are just beginning to give superintendents answers regarding the frequency and weight for a safe season.