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Introduction
Highbush blueberry is an important small fruit crop in North America. More than 30,000 ha are cultivated in the United States, and an additional 11,000 ha in Canada (USDA 2021). About 30% of the U.S. blueberry hectarage is located in the Pacific Northwest (PNW) region, mainly in Oregon and Washington. In the PNW region, blueberries are irrigated by overhead sprinkler or drip irrigation systems; the latter is gaining popularity (Bryla et al. 2011). Irrigation is essential for the commercial production of blueberries because the crop is sensitive to water deficits, probably associated with its shallow root system located primarily in the top 0.4 m of soil (Bryla and Strik 2007). Plants are spaced at 3 m between rows and from 0.9 to 1.2 m within the row to allow ample sunlight into the canopy (Strik 2007). Sawdust mulches are usually applied to the soil surface in a 3-m band at 18 cm depth after planting and reapplied when needed to maintain a depth of at least 12 cm, and the soil within the planting rows is never disturbed (Strik 2007). PNW blueberry growers have identified field bindweed as a difficult-to-control weed species (DeFrancesco and Murray 2011).
Field bindweed is a perennial vining weed with vigorous growth and a deep root system that thrives in undisturbed soil and abundant light (Weaver and Riley 1982). This weed infests perennial and annual cropping systems and natural areas (Sosnoskie et al. 2020), and is distributed throughout the United States and Canada (Mitich 1991). Field bindweed dispersal occurs by seeds and root fragments (Buhler and Burnside 1987). In the PNW region, field bindweed growth is observed between April and November or until the first frost occurs. Field bindweed control in blueberry is limited to chemical control because cultivation equipment cannot be used without damaging blueberry plants. The current management strategy is to repeatedly apply postemergence herbicides such as carfentrazone or glufosinate during the season (Peachey and Moretti, personal observation) followed by hand removal. An herbicide that would provide season-long control of field bindweed would reduce herbicide drift, labor needs, and improve weed control and fruit yield and quality. Systemic herbicides such as glyphosate and 2,4-D can effectively control field bindweed, but multiple applications are required (Sosnoskie et al. 2020),...