Irrigation frequency and mowing height influence annual bluegrass in perennial ryegrass

Abstract Annual bluegrass ( Poa annua L.) is a winter annual weed with limited herbicide control options in cool‐season turfgrasses. This research evaluated the effect of irrigation frequency and mowing height on annual bluegrass cover in perennial ryegrass ( Lolium perenne L.) in 2019 and 2020 on a 3‐year‐old mixed stand in North Brunswick, NJ. Treatments were arranged in a 2‐by‐2 factorial in a randomized split‐plot design with mowing height (11 or 38 mm) as the main plot and irrigation frequency (once or thrice week −1 ) as subplot. From June to October each year, both irrigation frequency treatments were irrigated to 60% reference evapotranspiration minus rainfall. Soil volumetric water content was consistently lower in once week −1 irrigation treatments in both years. Annual bluegrass cover was affected by irrigation frequency and mowing height, but no interaction was detected. In October, annual bluegrass cover was reduced (47%) in once week −1 treatments compared to thrice week −1 treatments (59%). Additionally, annual bluegrass cover in October was reduced in treatments mown at 38 mm (46%) compared to 11 mm (60%). Irrigation frequency had no effect on turfgrass quality, green cover, or normalized difference vegetation index (NDVI); however, mowing height affected these response variables. When differences were present, all values were greater in the higher mown treatments. This research suggests reducing irrigation frequency reduces annual bluegrass cover without affecting turfgrass quality, green cover, or NDVI in the humid subtropical climate (near the Humid Continental climate zone). Additionally, increasing mowing height will reduce annual bluegrass cover.