Low carrier volume herbicide trials and UAAS support management efforts of giant salvinia (Salvinia molesta): a case study

Abstract

Expanding the current aquatic herbicide portfolio, reducing total spray volumes, or remotely delivering herbicide using novel spray technologies could improve management opportunities targeting invasive aquatic plants, where options are more limited. However, research on giant salvinia [Salvinia molesta (D. S. Mitchell)] response to foliar herbicide applications at carrier volumes ≤ 140 L ha-1 is incomplete. Likewise, no data exists documenting S. molesta control with unoccupied aerial application systems (UAAS). Following the recent >100 ha incursion of S. molesta in Gapway Swamp, North Carolina, a case study was developed to provide guidance for ongoing management efforts. In total, three field trials evaluated registered aquatic and experimental herbicides using a 140 L ha-1 carrier volume. Select foliar applications from UAAS were also evaluated. Results at 8 weeks after treatment (8 WAT) indicated the experimental protoporphyrinogen oxidase inhibitor, PPO-699-01 (424 g a.i. ha-1), in combination with endothall dipotassium salt (2370 g a.e. ha-1) provided 78% visual control, whereas control when PPO-699-01 (212 g a.i. ha-1) was applied alone was lower at 35%. Evaluations also showed diquat (3136 g a.i. ha-1) alone, glyphosate (4539 g a.e. ha-1) alone, and metsulfuron-methyl (42 g a.i. ha-1) alone achieved 86 to 94% visual plant control at 8 WAT. Sequential foliar applications of diquat, flumioxazin (210 g a.i. ha-1), and carfentrazone (67 g a.i. ha-1) 6 wk following exposure to in-water fluridone treatments were no longer efficacious by 6 WAT due to plant regrowth. Carfentrazone applications made from a backpack sprayer displayed greater control than applications made with UAAS at 2 WAT deploying identical carrier volumes; however, neither application method provided effective control at 8 WAT. Additional field validation is needed to further guide management direction of S. molesta control using low carrier volume foliar applications.