Irrigation frequencies and reference evapotranspiration replacement affecting annual bluegrass encroachment in perennial ryegrass in western Oregon

Abstract

Annual bluegrass (Poa annua L.) encroachment may increase when turfgrass is maintained with excessive irrigation; however, with proper deficit irrigation, annual bluegrass germination and growth may be suppressed while desirable turfgrass is sustained. The goal of this project was to determine the optimal irrigation regime for suppressing annual bluegrass in perennial ryegrass (Lolium perenne L.) stands during the summer months. Two frequencies (once or four times a week) and rates (45% and 80% reference evapotranspiration [ET ref ] replacement) were used to assess the encroachment of annual bluegrass in perennial ryegrass maintained at 5 cm. Experimental design was a 2 × 2 factorial randomized complete block design with four replications. Preliminary findings suggest that irrigation applied once a week will reduce annual bluegrass compared to irrigation four times a week, while ET ref replacement had no effect on annual bluegrass encroachment. Findings also suggest that frequent irrigation will increase turfgrass quality and soil moisture in the top 3.8 cm.

Using survey results to direct future extension efforts in annual bluegrass management

“…Extension specialists or stakeholders in the cool‐season turfgrass zone would benefit most from research conducted by Cain et al. (2021), Kowalewski et al. (2022), and McNally et al.…”

“…These findings are similar to results produced by Brosnan et al (2022) in which the vast majority of survey respondents identified creeping bentgrass as the dominant turfgrass on putting greens across the United States. Extension specialists or stakeholders in the cool-season turfgrass zone would benefit most from research conducted by Cain et al (2021), Kowalewski et al (2022), andMcNally et al (2023), which specifically explored methods to control annual bluegrass within other cool-season turfgrass species. Most of the survey participants from the warm-season zone are managing hybrid ultradwarf bermudagrass greens, while creeping bentgrass greens dominated the responses from the transition zone (Table 2).…”

Comparing methods to quantify cover in turfgrass research

“…The point intercept method is a quantitative measure with an established history in plant ecology (Jonasson, 1988), which has been adapted into turfgrass research to measure cover. Adaptations of the point intercept method in turfgrass management include a frame with a grid of strings that is placed on the turfgrass surface (Figure 1; Cain et al., 2021; Gaussoin & Branham, 1989; Inguagiato et al., 2008; Schmid et al., 2017; Wang et al., 2018). Data can, then, visually be collected while looking down at the turfgrass surface at the intercept points.…”

“…These various adaptations of the point intercept method have been used to quantify percent cover of mixed stands of perennial ryegrass ( Lolium perenne L.) and annual bluegrass ( Poa annua L.) (Cain et al., 2021), tall fescue ( Schedonorus arundinaceus [Schreb.] Dumort.)…”

“…The point intercept method has also been used to quantify percent anthracnose ( Colletotrichum cereale ) on annual bluegrass (Hempfling et al., 2017; Inguagiato et al., 2008; Schmid et al., 2017; Wang et al., 2018). While several studies have used the point intercept method in turfgrass research, intercept spacing has varied substantially ranging from 5.0 to 13.3 cm (Cain et al., 2021; Gaussoin & Branham, 1989; Hunt & Dunn, 1993; Inguagiato et al., 2008). Increasing intercept spacing will reduce the number of data points within a plot, which consequently reduces data collection time, but decreases accuracy.…”