Field horsetail (Equisetum arvense) management with an herbicide layering strategy in established cranberry field

Field horsetail (HT; Equisetum arvense) is the most problematic creeping perennial weeds (CPW) in cranberry production in British Columbia (BC). Due to their extensive underground root and shoot system, CPW are seldom controlled by a single herbicide application. This study aims to develop an effective herbicide layering strategy composed of broadcast applications of pre-emergent (PRE), post-emergent (POST) and/or post harvest (POST-H) herbicides to manage HT in established cranberry beds. The experiment was conducted at an established (~5 years old) cranberry farm in Pitt Meadows, BC, that was highly infested with HT. The herbicide treatments were timed with the phenological stages of the cranberry plant: 1) PRE of sulfentrazone (140.16 g ai ha-1) at pre-bud break; 2) POST#1 of Clopyralid (102 g ai ha-1) or mesotrione (100.8 g ai ha-1) at bud break; 3) POST#2 of mesotrine (100.8 g ai ha-1) in tank mix with sethoxydim (495 g ai ha-1) at hook stage; and POST-H of dichlobenil (4400 g ai ha-1) at dormant stage after harvest. Weed coverage assessments were conducted biweekly until harvest starting after the POST#2 application. Weed coverage was visually scored on a 0% (no coverage) to 100% (complete coverage) scale. This study demonstrated that excellent HT control (>95% control) was maintained until harvest (late September) when the POST-H treatment of dichlobenil was included, suggesting that the PRE herbicide application may not be necessary for HT control when a POST-H herbicide application of dichlobenil is included in the treatment. For example, the POST-H followed by POST treatments were as effective as the full layering treatments on HT control. Furthermore, the study demonstrates that POST-H herbicide of dichlobenil should be included for season-long HT management. Future studies should examine whether the POST-H application of dichlobenil can reduce the need for POST herbicides while providing excellent (>95%) season-long HT control.