Irrigation Frequencies and Reference Evapotranspiration Replacement Affecting Annual Bluegrass Encroachment in Perennial Ryegrass in Western Oregon

AbstractAnnual 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 [ETref] 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 ETref 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.