Semester of Graduation

Fall 2017

Degree

Master of Science (MS)

Department

Plant, Environment, and Soil Sciences

Document Type

Thesis

Abstract

Salvinia molesta is one of the world’s worst aquatic weeds and has cost Louisiana nearly $7 million worth of damage and economic impact each year. While aquatic herbicides and the biological control agent, Cyrtobagous salviniae, are the most efficacious control methods, there are limitations with each technology. Therefore, studies were conducted to evaluate insect mortality at upper and lower lethal temperatures and investigate integrated pest management (IPM) with insects and herbicides. Three Louisiana populations of C. salviniae were tested to evaluate cold tolerance and found that at 0°C, the Bayou Nicholas population was 1.3- and 1.4-times more cold tolerant at LT50 and LT90 (lethal time to kill 50 and 90% of test population) compared to the Houma and Natchitoches populations, respectively. At -5°C, the Bayou Nicholas population was 1.1- to 1.3-times more cold tolerant than the other populations. There were no differences between populations at -9°C. These findings demonstrate C. salviniae can survive at lower temperatures than previously reported. Growth chamber trials investigated the tolerance of C. salviniae at 35 to 50°C to determine impact of high temperatures on mortality. At 35°C, the LT50 was 27.5 hours of exposure, while at 40°C, the LT50 was 14.8 hours. As expected, mortality occurs more rapidly at higher temperatures (45 and 50°C). Mesocosm trials were conducted to determine optimum timing for treating S. molesta with aquatic herbicides along with integrated management techniques compared with herbicides alone. An early season (April) herbicide application alone or in combination with C. salviniae was more efficacious than a late season application with or without C. salviniae. Glyphosate + diquat was efficacious against S. molesta at both application timings. Although C. salviniae alone was capable of reducing plant biomass, higher efficacy was achieved when used in conjunction with herbicides. Insect densities were highest at 6 and 9 weeks after treatment (WAT) regardless of treatment; however, the penoxsulam + C. salviniae treatment produced the lowest insect density overall. In addition, flumioxazin was efficacious in both trials and offers an alternate mode of action to treat S. molesta.

Date

10-30-2017

Committee Chair

Griffin, James

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