Using local weather stations to generate growing degree‐day data to predict the flowering pattern of an annual bluegrass fairway in Michigan

Abstract

Six 1-yr observational studies were conducted from 2001 to 2006 at the Hancock Turfgrass Research Center in East Lansing, MI to characterize the timing, duration, and amplitude of annual bluegrass (AB) (Poa annua L.) seedhead emergence in a 10-to 15-yr-old AB fairway. The objective of this research was to collect data that could be used in the development of a growing degree-day (GDD) model to predict AB seedhead emergence at other locations by using readily available weather station data. New GDD models were compared with previously published models. Plots were established on two adjacent perennial stands of AB maintained at 1.5 cm, receiving 0.5 to 0.6 cm of automatic daily irrigation throughout the growing season and 120 kg N ha -1 yr -1 from 2001 to 2006. The soil type is a Marlette sandy loam (fine-loamy, mixed, semiactive, mesic Oxyaquic Glossudalf). Line intersects and visual estimations of seedhead cover were evaluated multiple times throughout the spring seedhead emergence period. A base temperature of -5 ˚C most accurately predicted the onset, peak duration, and completion of the AB seedhead emergence period for all 5 yr. The final model flowering rate = (-3.331599 × 10 -6 × gdd 2) + (6.968782 × 10-3 × gdd) + -2.841894, accurately predicted (R 2 = .64) flowering stages of an AB fairway turf over 6 yr in Michigan.

Maximizing seedhead suppression of Poa annua L. in Michigan through use of growing degree‐days to predict optimum application timing for ethephon and ethephon plus trinexapac‐ethyl

“…As the climatic conditions varied from year to year, the application date was converted to growing degree‐days (GDD). A base temperature of –5 °C (GDD –5 ) was used, as it had previously been shown to provide the best fit to the response of seedhead formation in this AB population (Calhoun, 2010). In this way, GDD values for each application date could be compared from year to year and potentially extrapolated to other locations.…”

Pre‐snow and post‐snow applications of ethephon in winter enhance the suppression of annual bluegrass seedheads

“…The treatments in each experiment included an untreated check and an industry standard two-application spring program treatment of ethephon (5 fl oz 1,000 ft −2 ) + trinexapac-ethyl (0.125 fl oz 1,000 ft −2 ) (hereafter referred to as the spring program). Except in two experiments where weather or golf course maintenance practices interfered, the initial spring program application was made at 300 to 450 growing degree-days (GDD 32F ) from 15 February (Table 1) following the model for annual bluegrass seedhead control in northern climates (Calhoun, 2010). This was different from Reicher et al (2020), who used a 1 January biofix, and Askew (2017), who used 50 GDD 50F to time the spring treatments.…”

“…Van Dyke, unpublished data, 2022). A post‐snow application may keep plants regulated during warm periods in early spring with variable weather when GDD are accumulating ahead of the current seedhead model (Calhoun, 2010). The biological significance of GDD that accumulate ahead of the model are not yet known, but rogue AB seedheads have been found by this author in Utah during early February on greens clear of snow, and supports the theory that floral induction can occur during winter (Askew, 2017), including in regions with snow cover (Raudenbush et al., 2020).…”