Weed Management in Arizona Nurseries

Current weed management needs in Arizona nurseries assessed and research areas identified through surveys, interviews, and visit to nursery sites. Compared to other management issues in nursery production, weed management is still a major production challenge in Arizona nursery; with Chamaesyce prostrate (prostrate spurge), Cardamine hirsute (bittercress) and Baccharis sarothroides (desert broom) listed as major problems in that order. Interviews, surveys and field visits reiterated that prostrate spurge is the number one problem in container nursery production. Nursery growers in Arizona have tried various pre-emergence herbicides to control spurges, but reported verbally that none of the chemicals has given satisfactory control of prostrate spurge. During the field visits, it was common to see field grown nursery stock, infested with spurge weeds and that a high level of control is demanded to manage competition from such weeds, and to keep field appearance attractive. First it became apparent that spurge is number one problem challenging their production and plant marketability. Second, herbicides and mulches play a critical role in managing weed populations but there are issues related to sanitation, calibration, rate of application, time and uniform application of herbicides. Herbicide evaluations at two nursery sites in Phoenix, AZ indicated that opportunities for improved control do exist, if grower use proper calibration, rate of application, time and uniform application of herbicides, with granular formulations of pre-emergence herbicides such as indaziflam (Marengo G) which had long last effect on weed pressure for at least 3 months after treatment application or with currently used herbicides such as the combination of dimethenamid + pendimethalin (FreeHand 1.75G) which resulted in a weed free plots until eight weeks after treatment. Mulches proved as effective as herbicides and resulted in more than 90% control of spurges at least for eight weeks after treatment. Finally, we conclude that effective weed management in nursery crops should involve a combination of management options such as sound sanitary, cultural practices, and proper use of mulches along with proper use of herbicides.