Date of Award

12-1973

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Plants, Soils, and Insects

Major Professor

Larry S. Jeffery

Committee Members

Clifford C. Amundsen, David L. Coffey, William A. Krueger, John H. Reynolds

Abstract

The rates of disappearance of 1,1-dimethyl-3-(a, a, a-trifluoro-m-toly1) urea (fluometuron) and the propylene glycol butyl either esters and a triethylamine salt of (2, 4, 5-trichlorophenoxy) acetic acid (2, 4, 5-T) from the application site in field plots and lysimeters were determined. Residual herbicide concentrations were estimated for field plot soil, runoff water collected in the plots after rainfall, and permanently impounded drainage water from the plots. Bioassays, spectrophotometry, and gas-liquid chromatography were utilized to detect residual concentrations of the three compounds. Linear and multicurvilinear equations were developed from known concentrations of the herbicide for predictions of residue amounts in the field plots and lysimeters. The effects of the herbicides on forage sorghum [Sorghum bicolor (L.) Moench, 'Pioneer 931'] plant densit and the relationship of stand to forage yield were evaluated.

Preemergence application of fluometuron and 2, 4, 5-T reduced forage sorghum plant density to 75 and 43 percent of the control, respectively. The annual mean yield of oven-dry forage was 824 g/m2. There were no differences between forage yields from treated and untreated plots or between weed-free and weedy control plots when means were tested at the 0.05 level of probability.

The herbicides applied to the surface of Etowah silt loam were detected in the 0-1 cm depth of the plot soil within seven days of application. After 60 days no residue could be detected in the 0-1 cm zone. Fluometuron and 2, 4, 5-T herbicides present in the 0-15 cm soil zone and fluometuron in the 30-45 cm soil zone 14 days following application were degraded or leached from the sampling area in seven months. Fluometuron was present on day 210 following initial herbicide application but only in plots which were resprayed during the season.

The mean concentration of 2, 4, 5-T detected in impounded water was 0.04 ppmw. Detectable amounts of 2, 4, 5-T were not present in fresh runoff water collected in the plots. The ester formulation of 2, 4, 5-T dissipated more slowly in the impounded water than it did in field plot soil. No 2, 4, 5-T residues were detected in water seven months following herbicide application.

No detectable quantities of fluometuron residues were found in runoff and impounded water from the field plots 60 days following initial herbicide application. Fluometuron was degraded as rapidly in water as it was in soil.

Residual fluometuron and 2, 4, 5-T of both formulations were present in lysimeter percolation water 1 to 16 days following application to the soil surface. No detectable residues were present in lysimeter percolation water 90 days following herbicide application.

The data collected in this study indicate that the herbicide treatments did not permanently modify the application site or the nontarget sites to which the compounds migrated. No residual compound from the initial herbicide application could be detected at the end of the crop season.

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