Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)


Plant Science

First Advisor

W.E. Arnold


Studies were conducted to measure efficacy and economics of selected herbicide treatments for leafy spurge control in pasture, and to characterize the interaction of ammonium sulfate and glyphosate for quackgrass control. Several treatments resulted in leafy spurge control exceeding 90% in the tested pasture. Mean herbage dry-weight yield in treated plots was 2340 kg/ha, a 67% increase over untreated plots. Forage yields did not significantly differ among treatments controlling 90% or more leafy spurge. Marginal net return over marginal cost from herbicide treatments ranged from $35 to loss of $63/ha. Treatments providing satisfactory leafy spurge control with minimum economic risk were annual spring applications of 2, 4-D at 1. 7 kg/ha or dicamba + 2, 4-D at 0.6 + 1.1 kg/ha, and biannual application of 2, 4-D at 0.8 kg/ha. Addition of ammonium sulfate at rates of 1.4 to 5.6 kg/ha to glyphosate spray solutions of 0.22 to 0.68 kg/ha significantly improved quackgrass control over glyphosate alone at the same rates. An approximate doubling of activity was observed at low glyphosate rates. Generally any ammonium sulfate rate from 1.4 to 5.6 kg/ha produced similar effects. Since ammonium sulfate was not phytotoxic to quackgrass, the observed interaction between ammonium sulfate and glyphosate was an enhancement of glyphosate by ammonium sulfate. Electrolyte leakage from quackgrass leaves treated with ammonium sulfate and glyphosate was greater than from leaves treated with glyphosate alone. Absorption of 14C-glyphosate increased in solutions which contained ammonium sulfate. Translocation of 14C-glyphosate was not significantly affected by ammonium sulfate. More plastoglobuli were found in chloroplasts of plants 80 hr after treatment with glyphosate plus ammonium sulfate than in those treated with glyphosate. Based on these tests, ammonium sulfate enhancement of glyphosate is most likely from increased absorption of glyphosate into quackgrass leaves caused by increased cell membrane permeability due to the ammonium sulfate.

Library of Congress Subject Headings

Plants, Effect of glyphosate on
Weeds -- Control -- South Dakota




South Dakota State University