Seedhead Development of Three Warm-Season Turfgrasses as Influenced By Growing Degree-Days, Photoperiod, and Maintenance Regimens

Seedheads of warm-season grasses can reduce the quality of golf course turf. The objectives of this research were to evaluate environmental conditions associated with seedhead production of three warm-season turfgrasses maintained at various mowing heights (0.6 or 1.3 cm 2 d wk⁻¹, 3.8 cm wk⁻¹, or no mowing) over a 3-yr period. Photoperiod was more influential on initial seedhead development of ‘TifGrand’ bermudagrass [Cynodon dactylon (L.) Pers. ´Cynodon transvaalensis Burtt-Davy] and ‘Sea Isle 1’ seashore paspalum (Paspalum vaginatum Sw.) than calendar date or growing degree day (GDD) accumulation. Across all mowing heights, initial seedhead emergence began at 13.5-h photoperiod in 2013 and between 13.8 and 14.2 h in 2014 and 2015. Calendar date and GDD had stronger correlations than photoperiod with seedhead production from January until summer for bermudagrass and seashore paspalum at all mowing heights except for the 0.6 cm 2 d wk⁻¹. ‘Diamond’ zoysiagrass [Zoysia matrella (L.) Merr.] exhibited two major flushes of seedhead emergence that began with photoperiods of ~12.8 h in fall and spring. The GDD on dates of initial seedhead emergence in spring and fall ranged from 167 to 196 and 1949 to 2230 (base model 10°C on 1 January), respectively, in all years across mowing regimens. Zoysiagrass seedhead production had the highest correlation with GDD in spring and with photoperiod in fall. Overall, photoperiod triggers initial seedhead emergence of bermudagrass and seashore paspalum, but GDD is more influential on seedhead production in summer. The emergence of Diamond zoysiagrass seedheads in spring was associated with calendar date, GDD, and photoperiod, but emergence in fall was dependent on photoperiod.