Adsorption of tebuthiuron N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N’-dimethylurea appeared to be related to organic matter and clay content. After six successive desorption extractions, 40% of the tebuthiuron was adsorbed in soil with 4.8% organic matter but less than 1% was adsorbed in soil with 0.3% organic matter. Differences in adsorption were also reflected in the activity of tebuthiuron on soybeans [Glycine max (L.) Merr.] and corn (Zea mays L.) where it took 4.9 and 9.5 times as much tebuthiuron, respectively in soil with the greater adsorption to reduce growth by 50%. Soil mobility of tebuthiuron was identical to fluometuron[1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl),urea] in three soils tested. Soil mobility of herbicides was greater in soil with low organic matter and low clay content. Both temperature and soil moisture had an effect on persistence of tebuthiuron. Greater dissipation occurred at 15% soil moisture and 30 C than at lower moisture and temperature levels.

Single applications of several herbicides were compared after 12 to 48 months for control of chamise (Adenostoma fasciculatum H. & A.) and redshank chamise (Adenostoma sparsifolium Torr.). Glyphosate [N-(phosphonomethyl)glycine] provided more effective control and canopy reduction than any other herbicide tested. Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} and DX-1108 (ammonium ethyl carbanoylphosphonate) were also effective for control of chamise. Reduction in chamise canopy without leaf necrosis was observed with DPX-1108. Any herbicide tested could provide an alternative to currently used herbicides for chamise suppression.

Copper sulfate (CuSO4 · 5H20) was used as a tracer to determine soil sample variation and the effects of incorporation and seedbed preparation practices on the horizontal distribution of broadcast herbicide sprays. A Dubbs very fine sandy loam soil was sprayed with 14.1 kg/ha copper (as CuSO4 solution) and 19 mm diameter soil core samples were taken to a depth of 15 cm after spraying, after single or double disk-harrow incorporation, and after incorporation followed by bedding and row leveling. Cores were systematically located along and across the center two rows of the plots and numbered according to position. Soil cores were weighed, extracted with 0.05 M Na2 EDTA and the extract was analyzed by atomic absorption spectrophotometry. For all samples, cores had a range of copper between 50 and 1000 μg, with a coefficient of variation of 47%. Disk-harrow incorporation decreased the copper found in the center of the harrow path by nearly 50%. Bedding followed by row leveling did not change the tracer content of cores but decreased soil core densities. Disk-harrow incorporation may redistribute a herbicide that is initially applied evenly, producing areas of poor weed control and/or crop damage. This observation was confirmed in a field bioassay using trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and wheat (Triticum aestivum L. ‘Coker 6815′).