Page 10 - GreenMaster Spring 2022

The discovery that frequent rolling decreased dollar spot was the most astounding and useful cultural practice discovery since Old Tom Morris noticed topdressing the turf with sand improved conditions on his greens.
“...research indicate areas with the most dollar spot pressure should be irrigated lightly each night, shortly after sunset to presumably lengthen the time of increased volumetric moisture content in the soil”
savvy enough to incorporate Paul’s findings into an irrigation study. In 2011, Nancy Dykema initiated a 3-year master’s study focusing on the impact of irrigation timing on disease.
Her treatments included light- frequent irrigation compared to deep infrequent irrigation and the effect each had on dollar spot. Specifically, her treatments were irrigation applied daily at 10pm, applied daily at 5am, and applied 2 times per week at 10pm. All treatments received the same total amount of irrigation weekly (and seasonally).
Among her results, irrigating at 10pm nightly resulted in the least amount of dollar spot while irrigating infrequently at night resulted in the most dollar spot. Certainly, you cannot irrigate an entire golf course at the same time, however, any superin- tendent that has been at the same course for multiple years knows their troublespots.ResultsfromNancy’s researchindicateareaswiththemost dollar spot pressure should be irrigated lightly each night, shortly after sunset to presumably lengthen the time of increased volumetric moisture content in the soil without extending the leaf wetness period and, therefore, minimizing the disease pressure.
should be used sparingly if at all. I did not anticipate my results to refute those claims, I just knew there were no long-termrollingstudiesonfrequently sand-topdressed greens so I might as well be the first to gather the data. In the fall of 1996, I was as surprised as anyone else would have been when it became apparent that frequent rolling decreased localized dry spot and several turfgrass diseases including dollar spot.
As I began to share these astounding results they were met with skepticism, some degree of anger, and sometimes with thoughtful curiosity. It was Dr. Jim Crum, a soil scientist at Michigan State University (MSU), who asked, “Why do you think rolling decreases dollar spot? That’s what science needs to know”.
I followed his query with a list of possibilities that included frequent rolling: removes dew, guttation water, andleaflitterthatmissesthebucket duringthemorningmow,oritpossibly induces phytoalexin production in the plant (a form of defense against attack similar to white blood cells in humans following cuts) and finally rolling may alter the microbial popu- lation in the soil by increasing VMC.
Of those possibilities, I had reason to believe frequent rolling changed the microbial population in the soil and possibly increased phytoalexins in the plant too, however, determining how to measure these were beyond my skill set. 15 years later, enter Paul Giordano, master’s student under Dr. Joe Vargas of MSU and me.
Paul initiated research comparing plots single and double rolled in the morning as well as single rolled in afternoon. His results indicated that am and pm rolling decreased dollar spot similarly thus debunking the impact of dew, guttation, and leaf litter removal as a significant impact on dollar spot reduction. Additionally, Paul found that double rolling increased volumetric moisture con- tent (VMC) slightly more than single rolling which increased VMC slightly more than not rolling. Along those same lines, numerous bacteria populations were increased by frequent rolling which corelated with the increase in VMC.
Nancy Dykema has been the research technician for Dr. Vargas for over 30 years, and she was privy to Paul Giordano’s findings. Given that resume, it’s understandable she was
10 • CGSA • GreenMaster