Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)



First Advisor

Y.A. Greichus

Second Advisor

R.A. Moore


Purposes of this study were to find an effective herbicide for control of grassy weeds in a pasture, to adapt known laboratory procedures for analyzing residues and to determine amounts of residues during the growing season in treated plots. Nine herbicides were screened for controlling grassy weeds, primarily downy brome (Bromus tectorum L.) in a native pasture. Data indicated 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) applied postemergence at 1 lb/A was the most effective at 85% control. The following year, atrazine, 2-chloro-4, 6-bis­ (ethylamino)-s-triazine (simazine) and 2, 2-dichloropropionic acid (dalapon) each at 1, 2 and 3 lb/A were applied preemergence to switchgrass pasture. Of primary concern was control of grassy weeds; downy brome, green foxtail (Setaria virdis (L.) Beauv.) and yellow foxtail (Setaria glauca (L.) Beauv.). Atrazine effectiveness remained nearly constant through the summer with 50% grassy weed control. Simazine control was not significantly (P < .05) different from that of atrazine. Dalapon effectiveness decreased from 90% to 61 % and gave significantly (P < .05) higher percent control than either triazine. Atrazine and simazine were significantly (P < .05) higher in broadleaf weed control than dalapon. Atrazine and simazine caused no injury to the switchgrass. Dalapon, however, resulted in severe injury or death to the desirable grass. All herbicides increased in effectiveness as the rate of application increased. Herbicidal carry over as recorded in July 1970 was evident. Laboratory procedures for atrazine and simazine residue analysis included column, thin-layer and hydrogen-flame gas chromatography. Dalapon was analyzed using electron capture gas chromatography. No recordable atrazine and simazine residues (less than 5 ppm) were found in vegetative samples beginning with the June harvest. Dalapon applied in May at 1, 2 and 3 lb/A decreased to less than 3 ppm in late summer harvest.

Library of Congress Subject Headings

Weeds -- Control



Number of Pages



South Dakota State University