Date of Award

December 2019

Document Type


Degree Name

Master of Science (MS)


Environmental Engineering and Earth Sciences

Committee Member

Lambert B. McCarty

Committee Member

William C. Bridges

Committee Member

Matthew A. Cutulle


Golfers have steadily increased demands for putting green quality, including distance and smoothness. ‘Diamond’ zoysiagrass has emerged as a viable C4 turfgrass to be used by golf courses as putting greens or fairways and tees. ‘Diamond’ zoysiagrass exhibits multiple benefits over other C4 and C3 turfgrasses, but an undesirable trait is seedhead production.

Three studies were conducted at Clemson University from April 2018 to November 2019 to investigate the effects of plant growth regulators (PGRs) on ‘Diamond’ zoysiagrass’ turf quality (TQ), lateral recovery and seedhead production. Study 1 tested PGRs in a field setting on the TQ, seedhead production and root mass of a ‘Diamond’ zoysiagrass putting green. Study 2 tested PGRs on the TQ, seedhead production, clipping and root mass of ‘Diamond’ zoysiagrass in a greenhouse setting. Study 3 tested PGRs effects on the lateral growth of ‘Diamond’ zoysiagrass.

All three studies included treatments of trinexapac-ethyl (TE), prohexadione-calcium (PC), paclobutrazol (PB), flurprimidol (FL), ethephon (EP) and simazine (SI). The first study determined initial seedhead production was best predicted by 12.4 h photoperiod but accumulated growing degree days (GDD) was also fairly accurate. Compared to untreated, seedhead count was reduced through treatments SI and SI + TE by 80 and 75%, respectively, during fall seasons. Treatments did not consistently increase TQ above untreated. In fall 2018 at 14 days after treatment (DAT), SI and SI + TE decreased TQ to 5.5 and 5.3, respectively, significantly below the untreated’s rating of 7. However, in fall 2019 at 14DAT, SI and SI + TE were similar to control. Normalized difference of vegetative index (NDVI) reflected similar trends of TQ.

Study 2 illustrated 4 applications of TE, SI, PC, FL and SI on ‘Diamond’ zoysiagrass improved TQ to 7.9, 7.9, 7.8, and 7.8, respectively, all significantly greater than untreated’s 6.9. At this date EP reduced TQ to 5.6, significantly below untreated. Seedhead count after 5 applications was decreased by SI by 63% compared to the untreated, consistent with study 1. Interestingly, TE also reduced seedhead count by 41% below untreated, while EP increased count by 68% above untreated. Study 3 revealed at 16 weeks after initial treatment (WAIT) lateral recovery was decreased by FL, TE, PC, and PB by 20, 14, 12, and 11%, respectively, from untreated.



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