Dissertation - University Access Only
Doctor of Philosophy (PhD)
Department / School
Sharon A. Clay
Leafy spurge (Euphorbia esula L.) is an exotic, herbaceous, perennial weed that reduces rangeland productivity. The extensive root system is responsible for the plant's perennial nature and, therefore, is the target of control attempts. Chemical and mechanical methods were evaluated as alternatives to conventional herbicide treatments for effectiveness in reducing leafy spurge growth and root carbohydrate reserves as well as promoting grass production. Soil texture preferences of the leafy spurge biological control agents Aphthona nigriscutis and Aphthona cyparissiae were evaluated from open release site sweep net samplings collected by several state and federal agencies. The ability of these two Aphthona species to establish in a specific habitat was evaluated by determining larval densities in the fall and spring following adult infestation of enclosed cages. Black plastic smother, mowing at 2 and 4 week intervals, and biweekly applications of 2,4-D at 0.11 kg ha-1 reduced leafy spurge stem density, biorrass, and crown and root total nonstructural carbohydrate (TNC) levels compared to a single application of 1.12 kg ha-1 2,4-D and an untreated control. Grass biomass was greatest in plots treated with biweekly 0.11 kg 11a-1 2,4-D treatments in 1992. In comparison, black plastic smother killed all of the grass by the end of the 1992 growing season. In 1993 one-half of each plot was allowed to recover from 1992 treatments. Leafy spurge recovered from the black plastic treatment rapidly, while grass recovered slowly. Leafy spurge recovered well from the mowing and biweekly 0.11 kg ha-1 2,4-D treatments but grass biomass in these plots was greater than the control. Crown and root TNC were affected by alternative control methods, but the magnitude and pattern of the affect was different than leafy spurge stem density and biomass reduction. In 1992, crown and root TNC levels increased from the first sampling date in control plots. However, crown TNC did not increase in mow 4 week and 2,4-D plots. Root TNC increased from the first sampling date in all treatments except the smother plots in 1992. In 1993 crown TNC increased in the control and two 2,4-D treatments while all treatments allowed root TNC to increase during the 1993 growing season. Crown TNC increased in all recovery plots except mow 4 week and 2,4-D 1X and root TNC increased in the recovery plots of all treatments. Numbers of Aphthona spp. larvae recovered from microcages in the fall and spring were highly variable. Numbers of larvae recovered in the fall ranged from 0 to 44 and in the spring from 0 to 62. Larval head capsule width was greater in larvae from the spring than from the fall, indicating the larvae had grown. The spring-harvested cage with 62 larvae present had no living leafy spurge root tissue in it. Aphthona beetles released at open sites on coarse-textured soil became established more frequently than Aphthona spp. beetles released on medium- and fine-textured soil.
Library of Congress Subject Headings
Leafy spurge -- Control
South Dakota State University
Scholes, Chad Michael, "Suppression of Leafy Spurge (Euphorbia Esula L.) With Alternative Chemical, Mechanical, and Biological Methods" (1996). Electronic Theses and Dissertations. 202.