‘Tracy′, ‘Tracy-M′, and ‘Centennial′, soybean [Glycine max (L.) Merr.] cultivars were evaluated under greenhouse and field conditions for their tolerance to metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one]. The I50 (50% injury) concentration of metribuzin, as determined in nutrient culture, for Tracy-M was more than three times the I50 for Tracy, but was equivalent to the I50 for Centennial. Data from greenhouse and field studies on Sharkey clay and Dundee silt loam soils indicated that Tracy-M was more tolerant to metribuzin than its parent selection, Tracy, but no more tolerant than Centennial when metribuzin was applied preplant soil incorporated or surface preemergence alone or in combination with several dinitroaniline herbicides.

The concentration of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} residue in Miller clay and Lufkin fine sandy loam was determined at various intervals following incorporated and nonincorporated applications in the field. Low levels of fluridone were present in Miller clay after 250 days while up to 25% remained in Lufkin fine sandy loam 385 days after treatment. Incorporation of fluridone increased its persistence in, Lufkin fine sandy loam but not in Miller clay. Fluridone degradation in Miller clay and Lufkin fine sandy loam was more rapid in the field than under controlled conditions. Fluridone degradation in sterilized Brennan fine sandy loam and Hidalgo sandy clay loam was significantly slower than in nonsterilized soil kept under the same conditions. These differences were not observed in Lufkin fine sandy loam and Miller clay.

Experiments were conducted to determine the energy requirements and the most effective rotary tiller configuration for incorporating cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile} on an 18-cm band centered on top of the previous year's corn (Zea mays L.) ridge. When the rotary tiller was operated full width at a 10-cm depth, the least cyanazine concentration was found in the center of the ridge, and the greatest concentration was found between ridges. The treatment having the greatest cyanazine concentrations in the center of the ridge and the least in the inter-row between ridges consisted of a ridge cleaner, a cyanazine application, and the rotary tiller configured to till a. 30-cm strip on the center of the ridge with a rotor enclosure. Energy requirements for operating the rotary tiller increased as the depth of operation increased, and the 10-cm depth of operation required less energy than two passes with a tandem disk.

Field studies were conducted for 3 yr to evaluate the persistence of metolachlor and alachlor applied to ‘Centennial’ soybean and to determine their residual effect on ‘Mars' rice. At labeled use rates of metolachlor at 2.8 kg ai/ha and alachlor at 3.9 kg ai/ha, soil residue levels in the fall 5 months after application on Crowley and Midland silt loam soils averaged 0.04 and 0.05 ppmw, respectively. Metolachlor fall soil residues averaged 3.5 times higher when applied at 5.6 and 11.2 kg/ha compared to 2.8 kg/ha, but residues for labeled and double rates of alachlor were similar. In the spring 9 months after herbicide application, soil residues averaged over years did not exceed 0.06 ppmw. The 3-yr rice yields were not affected by residual metolachlor or alachlor.

Six substituted dinitrobenzamine herbicides, including butralin [4-(1,1-dimethylethyl)-N-(1-methylpropyl)-2,6-dinitrobenzenamine], dinitramine (N4,N4-diethyl-α,α,α-trifluoro-3,5-dinitrotoluene-2,4-diamine), fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)aniline], pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], and trifluralin (α,α,α,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), were evaluated as directed broadcast sprays applied and soil incorporated at time of last cultivation (layby) of cotton (Gossypium hirsutum L. ‘Acala SJ-2’). At the rates used, all herbicides provided more than 90% control of annual grasses. During 1976 and 1977, control of redroot pigweed (Amaranthus retroflexus L.) and smooth pigweed (Amaranthus hybridus L.) ranged from 90 to 100% and none of the herbicides differed significantly in their effect. However in 1975, butralin at 1.1 kg/ha did not improve pigweed control when compared to the untreated control. None of the herbicides consistently controlled black nightshade (Solanum nigrum L.) and except pendimethalin, none caused detectable cotton injury. In 2 of 3 yr, pendimethalin caused enlarged growth of the cotton stem in the cotyledonary node area contacted by the herbicide spray. Stem breakage following wind occurred in about 5% of the cotton plants; however, the injury was not manifested by reduced yield. None of the herbicides influenced cotton yield. Residues from soil samples collected 4 months after herbicide application reduced growth of Japanese millet [Echinochloa crus-galli (L.) Beauv. var. frumentacea (Link) Wright]3 and grain sorghum [Sorghum bicolor (L.) Moench] 24 to 49%.

Two formulations of triallate [S-(2, 3, 3-trichloroallyl)diisopropylthiocarbamate] were evaluated for their effectiveness in controlling wild oat (Avena fatua L.) in spring wheat (Triticum aestivum L.) in 12 field experiments conducted between 1967 and 1978. Control of wild oat was greater with fall applications of triallate granules than liquid or with spring applications of either liquid or granules. Further-more, 1.1 kg/ha of triallate granules applied in the fall controlled wild oat as well as did 1.7 kg/ha of liquid triallate applied in the fall. Wild oat control with triallate was usually better when soil incorporated than when surface applied regardless of formulation or time of application. Triallate granules controlled wild oat similarly on either plowed ground or wheat stubble; whereas, liquid triallate controlled wild oat better on plowed ground than wheat stubble. A delay of 8 h in triallate incorporation did not reduce wild oat control with either formulation; however, a delay of 24 h reduced wild oat control with the liquid formulation.

For 3 yr, fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} at 0.1, 0.2, and 0.3 kg/ha, was applied with or without 0.6 kg/ha of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) before the preplanting irrigation for cotton (Gossypium hirsutum L.). Without trifluralin, fluridone at 0.1 kg/ha controlled less than 60% of annual grasses or redroot pigweed (Amaranthus retroflexus L.), but the 0.3-kg/ha rate controlled 90%. With trifluralin, fluridone at all rates controlled 98% of these weeds. Fluridone alone controlled 85% or more of black nightshade (Solanum nigrum L.). Fluridone did not alter cotton stand or yield. Fluridone residues 8 months after treatment reduced growth of several crops and weeds by 75% or more.

In a Crowley silt loam, between 30 kPa, continuous flood, and alternate flood laboratory treatments at 25 C, dissipation of incorporated oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-Δ2-1,3,4-oxadiazolin-5-one] varied little, with an average of 59% remaining after 20 weeks. In the greenhouse, subsurface application of oxadiazon reduced its phytotoxicity but increased its persistence up to four times more than with surface-applied oxadiazon. In the field, 50% of the surface-applied oxadiazon dissipated from the soil within 6 to 11 days when the soil was flush irrigated and then flooded, compared to 15 to 17 days when the soil was irrigated but not flooded in two rice (Oryza sativa L.) management systems. Oxadiazon dissipation in the field was greater during the first 2 or 3 weeks after application than in the laboratory study. This is explained at least partially by the lack of herbicide incorporation in the field.

The fate of field-applied herbicides, including losses in surface runoff with water and sediment, is highly dependent on herbicide properties. The two most important properties are soil adsorption and persistence. Adsorption affects the potential for a herbicide to be lost primarily with sediment, runoff water, or possibly leaching water. Solubility, often though not always inversely correlated with adsorption, is of secondary importance, although low solubility can limit transport with water. Persistence affects the time available to be lost in runoff. Studies have shown that for soil-applied herbicides; extraction into runoff water or movement with sediment takes place from a thin soil layer at the surface. In addition, for herbicides studied, there is little interaction between surface crop residue and applied herbicides, and washoff from the residue readily occurs with small amounts of rainfall. Runoff loss equals the volume of carrier (water or sediment) times the concentration in that carrier; therefore, practices that reduce either, or both, can reduce losses. Rate of application has been directly related to concentration and therefore loss. Reducing rate, such as by banding, soil incorporation, and avoidance of application to crop residue reduce losses. The choice of herbicide and herbicide formulation, in conjunction with application technology, as they affect properties, rate, and placement, play a large role in determining runoff loss. Runoff losses of herbicides that are strongly adsorbed and therefore transported mainly with sediment can be reduced by erosion control; runoff volume reduction can reduce losses with water of moderately to weakly adsorbed herbicides. Conservation tillage has potential to reduce both runoff and erosion. Timing of application relative to expected intense storms, both in the short and long term, can reduce the potential for runoff. If possible to determine thresholds, herbicide use could be avoided if weed infestation is below the economic effect level. Buffer or filter strips have the potential to reduce transport of herbicides lost from fields to surface water resources.

The formulation of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) encapsulated within a starch granule can reduce the loss in activity associated with the delayed incorporation of the emulsifiable concentrate formulation of trifluralin. Good weed control and high soybean [Glycine max (L.) Merr. ‘Wells II’] yields were obtained when a starch formulation of trifluralin was applied in the fall and incorporated at planting time the following spring. The cultural practices of shallow incorporation, delayed incorporation, and/or midseason cultivation intensified the weed control provided by a starch formulation of trifluralin. The adsorption of additional trifluralin onto the granule surface, cross-linking starch xanthate with a weak oxidant, and mixing granules with different release rates also increased initial control. Granules produced by the starch-calcium and starch-borate processes exhibited many of the same characteristics of granules produced by the older starch xanthate process, but are much less expensive to produce and do not require the use of the toxic carbon disulfide in the encapsulation process. The combination of an appropriate starch formulation of trifluralin with proper cultural practices provided good weed control from fall and spring applications of trifluralin.