Masters Theses

Date of Award

6-1981

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

L. S. Jeffery

Committee Members

Elmer L. Ashburn, David L. Coffey

Abstract

Field studies were conducted to determine: (1) a systematic approach to selectively control sicklepod (Cassia obtusifolia L.) in soybeans (Glycine max (L.) Merr.) utilizing preplant incorporated, preemergence, and postemergence applications of appropriate herbicides, (2) the competition effects involving removal of sicklepod plants at different times during the soybean growing season, and (3) production costs and net dollar return for each herbicide system. The herbicide systems and competition studies were conducted in 1980 at the Plant Science Field Laboratory at Knoxville and on a farm near Benton, Tennessee. Parameters measured were percent sicklepod control and soybean yield in the herbicide study, and sicklepod stand count and soybean yield in the competition study. Net dollar return was also determined for the study. At both locations the soybean cultivar 'Essex' was used. Metribuzin (4-amino-6-tert-butyl-3-(methylthio)-as-triazin- 5(4H)-one) plus vernolate (S-propyl dipropylthiocarbamate) applied pre plant incorporated followed by linuron (3(3,4-dichlorophenyl)-l-methoxy- 1-methylurea) plus 2,4-DB (4-(2,4-dichlorophenoxy) butyric acid) applied postemergence directed gave excellent control of sicklepod. Metribuzin mixed with either metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl) acetamide) or alachlor (2-chloro-2',6'-diethyl-N-(methoxymethyl) acetanilide) applied preemergence followed by linuron plus 2,4-DB applied postemergence directed, also gave effective sicklepod control. Generally, postemergence herbicide treatments such as acifluorfen (5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid), or toxaphene (chlorinated camphene containing 67-69% chlorine) used alone were not as effective in controlling sicklepod as they were when used following a preemergence herbicide. Better sicklepod control was achieved with toxaphene and acifluorfen when they were applied to sicklepod in the cotyledon or unifoliolate stage of growth. Generally, soybean yields were higher as more sicklepod control was achieved. Dollar net returns were generally higher where sicklepod was effectively controlled. Soybean yields were generally higher if soybeans were kept free of sicklepod for 4 or more weeks after planting.

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