Masters Theses

Date of Award

6-1977

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

Larry S. Jeffery

Committee Members

Laurence N. Skold, Elmer L. Ashburn, Frank F. Bell

Abstract

Chemical soil sterilization is one of the most important recent developments in weed control and interest from both the agricultural and industrial sectors is increasing. The problem of unwanted vetega-tion in roadsides, fence rows, rights-of-way, and building areas is complex and of great economic significance, particularly when the labor and machinery costs of nonchemical control are considered. This research compared the effectiveness of several herbicides used at selected rates for the purpose of soil sterilization. The study was initiated in the spring of 1976 at four Tennessee locations, i.e., Ames Plantation, Crossville, Knoxville, and Milan, with soil types at the above locations being Grenada silt loam, Tilsit loam, Dandridge shaly clay, and Loring silt loam, respectively. A randomized complete block design with three replications was used at each location. Percent bare ground and control of dominant weed species were measured by visual observation approximately each month during the ensuing growing season. Treatments include: amitrole (3-amino-s-triazole) at 5.6 kg/ha, atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-striazine] at 11.2 and 28.1 kg/ha, BAY 6579 H (N-[5-(ethylsulfonyl)-l,3, 4-thiadiazol-2-yl]-N,N'-dimethylurea), at 9.0 kg/ha, bromacil (5-bromo- 3-sec-butyl-6-methyluracil) at 16.8 kg/ha, diuron [3-(3,4- dichlorophenyl)-1,1-dimethylurea] at 11.2 and 22.4 kg/ha, fenac [(2,3,6-trichlorophenyl)acetic acid] at 13.5 kg/ha + paraquat (1,1'- dimethyl-4,4'-bipyridinium ion) at 0.6 kg/ha, karbutilate [tert-butylcarbamic acid ester with 3-(m-hydroxyphenyl)-1,1-dimethylurea] at 16,8 kg/ha, prometone [2,4-bis(isopropylamino)-6- methoxy-s-triazine] at 22.4 kg/ha, simazine [2,-chloro-4,6-bis (ethylamino)-s-triazine] at 11.2 and 28.1 kg/ha, tebuthiuron (N-[5-(1,1-dimethyethyl)- 1,3,4-thiadiazol-2-yl]-N,N'-dimethylurea) at 22.4 kg/ha, tetrafluoron (3-tetrafluoroethyoxyphenyl-N,N-dimethylurea) at 4.5 kg/ha + paraquat at 0.6 kg/ha, triclopyr ([(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid) at 6.7 and 10.1 kg/ha, and DPX-3674 [3-cyclohexyl-6- (dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] at 9.0 kg/ha. Bromacil, karbutilate and tebuthiuron exhibited 90% or better bare ground and control of dominant species including: johnsongrass, [Sorghum halepense (L.) Pers.], at Ames Plantation; bermudagrass, [Cynodon dactylon (L,) Pers.] and dallisgrass, [Paspalum dilitatum Poir.] at Milan; beaked panicum,[Panicum anceps Michx.], purpletop, [Tridens flavus (L.) Hitch.], broomsedge, [Andropogon supp.] and sericea lespedeza [Lespedeza cuneata (Dumont) D, Don] at Knoxville. BAY 6579 H and DPX-3674 effectively controlled bermudagrass and dallisgrass at Milan but not johnsongrass at Ames Plantation. Atrazine and simazine at 11.2 and 28.1 kg/ha as well as diruon at 11.2 and 22,4 kg/ha controlled shallow rooted annual broadleaf species but failed to control perennial broadleaf weeds and established grasses. Prometone and both rates of triclopyr exhibited very rapid knockdown activity as did those compounds mixed with paraquat. Neither compound exhibited much residual activity. Triclopyr was effective in controlling some perennial broadleaf species but failed to control grasses. A tabulation of the number of rhizome johnsongrass shoots per square meter made in April 1977 at Ames Plantation indicates that bromacil, karbutilate and tebuthiuron significantly reduced the number of johnsongrass shoots. After one year, only 5, 5, and 3 rhizome shoots per square meter, respectively, were recorded in plots treated with these chemicals, as compared with 122 rhizome shoots per square meter in the weedy check. From this research the following information was obtained: bromacil, karbutilate and tebuthiuron at rates of 16.8, 16,8, and 22,4 kg/ha, respectively, controlled tough perennial weeds and persisted in the soil for at least one year. BAY 6579 H and DPX-3674 at 9 kg/ha are excellent soil sterilants where bermudagrass is prevalent, but neither controlled johnsongrass. Amitrol T, atrazine, diuron, fenac, prometone, simazine, tetrafluoron, and triclopyr have individual merits as herbicides but at rates used in this study, do not warrant description as soil sterilants.

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