Field studies were conducted to determine suitability of flurtamone alone and in tank mixture with ethalfluralin for selective control of weeds in safflower. Flurtamone at 0.6 to 0.9 kg ha−1 controlled field pennycress, kochia, and Russian thistle. Flurtamone and ethalfluralin were compatible in tank mixture and provided comparable or superior control of wild oat, kochia, and field pennycress than either herbicide alone. Plant height, date of flowering, seed yield, and quality data indicated that safflower tolerated flurtamone alone up to 1.6 kg ha−1 and flurtamone tank mixed with ethalfluralin at rates as high as 1.1 plus 1.1 kg tar1, respectively. Safflower yield response to these herbicides was positive and reflected level of weed control attained with various treatments.

Experiments were conducted to determine the influence of nitrogen (N) fertility and winter wheat cultivars on weed infestations in a winter wheat-ecofallow sorghum-fallow rotation near North Platte, NE. Centurk 78 and Lancota winter wheat suppressed density and growth of barnyardgrass and green foxtail significantly more than Eagle winter wheat before and after wheat harvest. Increasing N rates applied to winter wheat decreased annual grass weed population and weed yields. However, 67 and 101 kg N ha−1 reduced winter wheat grain yields compared to 34 kg N ha−1. Plots treated at 2.8 plus 0.3 kg ai ha−1 of atrazine plus paraquat 31 d after wheat harvest had more barnyardgrass before grain sorghum planting in 1983 than plots treated 17 d after wheat harvest but the reverse was true for green foxtail after grain sorghum emergence in 1984. Increasing N rates from 34 kg ha−1 to 67 and 101 kg ha−1 in the previous wheat crop decreased weed density before and after grain sorghum planting. There was no advantage in weed control in the grain sorghum from applying N to winter wheat in the fall vs. spring.

Field research was conducted at Arlington, WI, in 1988 and 1989 to determine the influence of application time on weed control and residue carryover with imazethapyr in no-tillage soybean production. Imazethapyr at ≥ 55 g ai ha−1 applied early preplant controlled > 90% of the common lambsquarters, velvetleaf, and giant foxtail before no-tillage planting of soybean. Early preplant and sequential treatments with an early preplant component controlled ≥ 88% of all weeds for the entire growing season. Delaying the initial imazethapyr application until immediately after soybean planting reduced weed control compared to the early preplant treatments. Low level of weed control with planting time treatments appeared to be due to a lack of control of common lambsquarters emerged at the time of imazethapyr application and dry weather following imazethapyr application. No soybean injury from imazethapyr was observed and differences in soybean yield appeared to be due to differences in weed control. No significant carryover of imazethapyr was detected through a corn bioassay in the field.

The response of ‘C-20’ navy bean and ‘Frankenmuth’ soft white winter wheat grown in rotation to clomazone, imazethapyr, bentazon, and acifluorfen was examined. Clomazone at 560 and 430 g ai ha−1 plus 800 g ai ha−1 pendimethalin and 2000 g ai ha−1 chloramben visibly injured navy bean in 1 of 2 yr. However, navy bean seed moisture at harvest and yield was not reduced compared to the weed-free control. PPI and PRE treatments of 70 g ai ha−1 imazethapyr did not injure navy bean or reduce yield. Imazethapyr applied POST at 70 g ha−1 plus nonionic surfactant visibly injured navy bean. The addition of urea ammonium nitrate to imazethapyr enhanced visible injury and seed moisture compared to nonionic surfactant alone in 1 of 2 yr. However, seed yield was not reduced. Seed moisture at harvest was greater following treatment with 430 g ai ha−1 acifluorfen plus nonionic surfactant or urea ammonium nitrate and 140 and 280 g ha−1 acifluorfen plus 840 g ai ha−1 bentazon in 1 of 2 yr compared to the weed-free control, but yield was not reduced. Wheat yield was reduced in 2 of 2 and 1 of 2 yr by 560 g ha−1 and 430 g ha−1 clomazone, respectively, plus pendimethalin plus chloramben compared to the weed-free control. Wheat yield was not reduced by imazethapyr, bentazon, or acifluorfen.

Colorimetry, nephelometry, and chlorophyll assays of cultures of Chlamydomonas reinhardtii Dangeard, Chlorella pyrenoidosa Chick., and Scenedesmus quadricauda (Turp.) Bréb. were used as criteria for measuring algae growth. Among the four s-triazines studied, cyprazine appeared to be the most inhibitory to algae growth, followed by atrazine > simazine > cyanazine. Stimulatory effects of cyanazine, simazine, and cyprazine on chlorophyll content of C. reinhardtii and C. pyrenoidosa were also observed. Cyanazine was most stimulatory on both species but simazine also showed stimulation. Cyprazine was stimulatory only to C. reinhardtii at 0.22 μM concentration but apparently was inhibitory to C. pyrenoidosa at the same concentration. In one experiment, atrazine caused a slight stimulation in C. reinhardtii. Averaged over two consecutive experiments, however, atrazine was inhibitory. Chlorophyll content of the algae was found to be the best criterion for determining effect of the chemicals on algae growth. Continuous exposure of C. reinhardtii culture to the highest concentration of each of the four herbicides resulted in selection of algal lines having increased triazine tolerance.

The photolytic degradation of several imidazolinone herbicides in solution and on soil was investigated. Ultraviolet light caused 100% degradation of imazaquin, imazethapyr, and imazapyr, and 87 and 8% degradation of imazamethabenz and atrazine in aqueous solutions, respectively, after 48 h. The order of susceptibility to photolysis in decreasing order was imazaquin = imazethapyr > imazapyr > imazamethabenz > atrazine. In soil Studies, 45% of imazaquin and 52% of imazethapyr dissipated from moist sand after 48 h of exposure. Herbicide dissipation on air-dry sand and on field capacity and air-dry silty clay loam was less than 10% in most instances. Atrazine photolysis was not detected. This research indicates that photolysis of imidazolinone herbicides in solution is rapid. Photolysis on soil occurs readily on coarse-textured wet soils probably due to greater availability of the herbicide for photochemical alteration.

Metazachlor degradation in soil was studied in fields of spring barley, turnips, brussels sprouts, and leeks. Metazachlor in soil was transformed into 2-hydroxy-N-(2,6-dimethylphenyl)-N-(1H-pyrazol-1-yl methyl)-acetamide (compound 2), 2-chloro-N-(2,6-dimethylphenyl)-acetamide (compound 3), and 4,4′-methylenebis-(2,6-dimethylbenzenamine) (compound 4). Soil concentrations of compound 4 were always lower than 0.1 ppm. The half-life of metazachlor in the 0- to 10-cm soil layer was 1 to 3 mo. Metazachlor and compounds 2, 3, and 4 were not detected in the 10- to 20- and 20- to 30-cm soil layers. Metazachlor and metabolites (compounds) 2, 3, and 4 were not detected in barley grain or in the edible part of the vegetables. The sensitivity limit for these compounds was 0.02 ppm.

Adsorption and desorption of metribuzin and metolachlor were studied for 0- to 15- and 30- to 45-cm soil depths and at 5 and 28 C temperatures for two subarctic Alaskan agricultural soils. Surface soils had five to eight times the organic carbon content of deeper soils and had lower Freundlich isotherm slopes (1/n) for both herbicides. Surface soil Freundlich coefficients (Kf) were affected by both soil type and equilibration temperature, with soil type accounting for greater than 80% of the variation in Kf. Surface soil mean Kf values ranged from 1.5 to 2.4 for metribuzin and 4.4 to 9.2 for metolachlor. For soils from the 30- to 45-cm depth, neither soil type nor temperature affected Kf. Isotherm slopes for desorption were less than adsorption, indicating hysteresis. Regressions between desorption Kf and maximum herbicide adsorbed prior to desorption were highly significant with coefficients of determination (r2) between 0.50 and 0.99.

A system, including a specialized treatment vessel for pesticide uptake studies, was developed and experiments were carried out to determine the ability of Glomus intraradices (Schenck & Smith), G. vesiculiferium (Thaxter), and indigenous vesicular-arbuscular mycorrhizae (VAM) fungi to influence 14C-atrazine uptake and transfer to corn. Uptake by root systems with and without VAM infection was compared to uptake by VAM hyphal systems by controlling access to 14C-atrazine-treated soil. Hyphal systems of Glomus species were able to remove 14C-residue from soil and transfer these to corn. Amount of 14C-residue transferred to corn through hyphal systems was highly correlated to the level of VAM root infection which varied among VAM species. In root systems, variations in 14C-residue uptake resulting from mycorrhization were largely explained in terms of the negative correlation between level of infection and root mass located in 14C-atrazine-treated soil. Allocation of 14C-residue to shoot tissues of corn was greater when 14C-residues were taken up through root systems rather than through hyphal systems. There were significant effects of VAM species on 14C-residue compartmentalization between methanol extractable and nonextractable portions of corn tissues. Data from these experiments in a confined soil system were related to VAM cost-benefit relationships and indicate a significant role for VAM in determining atrazine fate in agricultural systems.