Semester of Graduation

Fall 2019

Degree

Master of Science (MS)

Department

SPESS

Document Type

Thesis

Abstract

The invasive aquatic fern giant salvinia (Salvinia molesta D.S. Mitchell) has been invading waterbodies across Louisiana and Texas since 1998. Recently, the non-aquatic herbicide metsulfuron-methyl was found to be highly efficacious against giant salvinia, but limited information is available on application techniques, use rates and concentrations, as well as its impact on non-target species. Therefore, a series of mesocosm experiments were conducted to further evaluate foliar and subsurface applications of metsulfuron against giant salvinia, as well as foliar applications of metsulfuron in combination with aquatic herbicides commonly used for giant salvinia control. When applied to the foliage of giant salvinia, metsulfuron provided ≥ 98% giant salvinia control by 8 weeks after treatment (WAT) at 10.5 to 168.2 g active ingredient (a.i.) ha-1. Metsulfuron was also compatible and highly efficacious in tank mix combinations with glyphosate, flumioxazin, diquat, and carfentrazone. All tank mixes increased speed of injury and plant death, but did not increase level of control. Subsurface applications of metsulfuron were also highly efficacious, and provided ≥ 98% control by 10 WAT at concentrations of 10 to 80 µg a.i. L-1. The calculated LD90 and EC90 (lethal dose and effective concentration to control 90% of the test population) values were 3.83 g a.i. ha-1 and 1.87 µg a.i. L-1 for foliar and subsurface applications, respectively. Outdoor mesocosm trials were also conducted to evaluate the sensitivity of non-target aquatic and terrestrial plants to metsulfuron as a foliar treatment, or in irrigation water. Foliar applications of metsulfuron at ≥ 10.5 g a.i. ha-1 resulted in ≥ 98% reduction in plant biomass of giant blue iris (Iris giganticaerulea Small.) and broadleaf arrowhead (Sagittaria latifolia Willd.), and ≥ 84% reduction of yellow water lily (Nymphaea mexicana Zucc.). Broadleaf cattail (Typha latifolia L.) was only impacted by rates ≥ 42.1 g a.i. ha-1. The non-target terrestrial plants vinca [Catharanthus roseus (L.) G. Don.], soybean [Glycine max (L.) Merr.], and cherry tomato (Solanum lycopersicum L.) were not impacted by metsulfuron treated irrigation water at concentrations ranging from 1 to 40 µg a.i. L-1, while iris was not affected until herbicide concentrations reached 40 µg a.i. L-1.

Committee Chair

Fontenot, Kathryn

DOI

10.31390/gradschool_theses.5023

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