Influence of shade on efficacy of aquatic herbicides for control of giant salvinia

• Published in: Journal of aquatic plant management 2024-01, Vol.62 (2), p.60-63
• Main Authors: Mudge, Christopher R, Pham, Korey D, P Sperry, And Benjamin
• Format: Article
• Language: English
• Subjects: Biomass; Diquat; Effectiveness; Floating plants; Foliage; Foliar applications; Freshwater plants; Glyphosate; Herbicides; High density polyethylenes; Leaves; Light; Light intensity; Luminous intensity; Mosses; Plant growth; Shade; Sunlight
• ISSN: 0146-6623
• DOI: 10.57257/JAPM-D-24-00011

Giant salvinia (Salvinia molesta) can be found in open water under full sunlight as well as under the dense canopy of trees across the southern United States. To date, most herbicides have been evaluated for efficacy against giant salvinia under full sunlight. Because most herbicides interfere with lightdependent processes, the influence of shade where plant growth is slower and herbicide activity could be hindered should be evaluated. Therefore, a mesocosm trial was conducted to determine the impact of reduced light on the efficacy of carfentrazone, diquat, flumioxazin, glyphosate, metsulfuron, and penoxsulam when applied to the foliage of giant salvinia grown under 0, 30, and 60% shade levels. At 7 wk after treatment (WAT), all herbicides reduced giant salvinia biomass 87 to 100% of the control when plants were cultured under 0% shade. Diquat and glyphosate efficacy was not impacted by light intensity, with biomass reduced $97% regardless of light treatment. There were no differences in control for plants grown under the full sunlight or 30% shade treatments and exposed to a foliar application of flumioxazin. However, giant salvinia control decreased by 16 and 27% when treated with carfentrazone and grown under 30 and 60% shade levels, respectively. The greatest impact on efficacy occurred when penoxsulam and metsulfuron were applied to giant salvinia grown under the 30% light intensity and biomass was only decreased 20 and 23%, respectively, compared to 63 to 92% control by these slow-acting systemic herbicides when grown under 30 and 0% shade. These findings suggest that light availability plays a crucial role in herbicide performance and herbicide selection is critical for managing this species in shaded areas.