Field studies at three locations across Nebraska showed that 2,3,6-trichlorobenzoic acid (2,3,6-TBA) leached readily into the soil profile. The herbicide was lost from the surface soil much more readily in central and western Nebraska than in eastern Nebraska even though rainfall was about twice as much at the last location. Volatilization was suggested as a possible reason for this loss of 2,3,6-TBA. There was a definite, but not complete, loss of 2,3,6-TBA from the three soil profiles between May 1960 and September 1961. Soybeans proved to be an acceptable bioassay plant for this herbicide in soil at 2,3,6-TBA concentrations of ½ to 2 ppmw.

As the seeds of leafy spurge (Euphorbia esula L.) increase in age after fertilization, their color changes from yellow to yellow with brown tips, to brown ends with a narrow yellow band, to brown with an orange band, and to a reddish-brown seed, followed in order by brown, gray-brown, gray, and finally, mottled. The last four are viable; the others are not. Mowing of leafy spurge to prevent viable seed production must be done before seeds have turned brown. Brown seeds appeared 10 to 13 days after fertilization depending upon seasonal conditions.

The fungus Scopulariopis brumptii Salvanet-Duval (MSU 42018) was isolated from a soil sample collected from the rhizosphere of a potted asparagus plant. When cultured 7 days in A-9 broth medium, the organism produced compounds phytotoxic to seeding dicotyledonous weeds (via foliar application) and to Chlamydomonas reinhardtii Dangeard. Three herbicidal metabolites, 3-hydroxybenzyl alcohol, 2-methylhydroquinone, and (+)-epiepoformin, were isolated by column and thin-layer chromatography (TLC) and structures confirmed by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic reasonance spectroscopy (NMR), and mass spectrometry (MS). Of the three compounds, (+)-epiepoformin was the most active, providing complete control of redroot pigweed and 88% control of white mustard when applied at 4.4 kg/ha.

Crown bud, tiller, and rhizome development was studied in 10 quackgrass biotypes at two stages (three-to four- and seven- to eight-leaf stages) of development to determine if differential development of these structures influenced control with sethoxydim and haloxyfop. There was a differential response among the 10 biotypes to both sethoxydim and haloxyfop at both stages of development. The biotypes differed in the number of crown buds, tillers, and rhizomes that formed at both stages of development. In the three- to four-leaf stage, the biotypes with the greatest number of crown buds were the most difficult to control. These results suggest that in the susceptible stage (three-to four-leaf) the quackgrass biotypes with the least number of crown buds will be the easiest to control; however, by the time all the biotypes reach the seven- to eight-leaf stage even the biotypes with the lowest number of crown buds have enough crown buds that they become difficult to control with either sethoxydim or haloxyfop.

Enzymatically isolated mesophyll cells of soybean [Glycine max (L.) Merr. ‘Kino’] and cotton (Gossypium hirsutum L. ‘Stoneville 1613 glandless’) were used to study the effects of three surfactants, I = ‘Sterox SK’ (polyoxyethylene thioether), II = ‘Renex 36’ (polyoxyethylene-6-tridecylether), and III = ‘WSCP’ [polyoxyethylene (dimethylimino) ethylene (dimethylimino) ethylene dichloride] alone or in combination with two herbicides, D-497 (1,1-dimethyl-4,6-diisopropyl-5-indanylethyl ketone) and oryzalin (3,5-dinitro-N4,N4-dipropylsulfanilamide) on cell permeability, photosynthetic 14CO2 fixation and cellular ultrastructure. Greatest amount of efflux of 14C-labeled material from soybean cells was caused by III, whereas other surfactants or herbicides produced only slightly higher effluxes than the controls. Mixtures of oryzalin-I or -II were the only combinations that enhanced efflux in soybean cells above that of cells treated with the surfactant or herbicide alone. However, on cotton cells all surfactants and oryzalin caused considerable leakage but no synergistic effects. Sugars were the predominant compounds leaked from the treated and control cells. Disorganization of all cellular membranes was caused by III whereas I and II disrupted only the chloroplast grana-intergrana thylakoids, causing abnormal grana. Herbicidal damage to the cell ultrastructure was minimal. Cells treated with combinations of surfactants and herbicides produced only those ultrastructural symptoms that the individual chemicals caused when applied alone. Photosynthetic CO2 fixation was inhibited in both cotton and soybean cells treated with surfactants and (or) herbicides. Interference with membrane integrity, either directly by interaction with membranes or indirectly by interference with cellular energy generating systems that maintain membrane integrity is the postulated mode of action of these surfactants and herbicides.

To determine if cell damage could account for chlorsulfuron inhibition of assimilate transport, the ultrastructure of companion cells and surrounding mesophyll cells was examined following chlorsulfuron treatment. Six hours after treatment of canola leaves, thylakoids in companion cells were swollen and chloroplast structures in mesophyll cells were disorganized. Three days after treatment, the treated leaves contained more starch granules in companion cells than corresponding control leaves, presumably as a result of reduced assimilate export. We conclude that the inhibition of assimilate export in chlorsulfuron-treated canola leaves is associated, at least in part, with the ultrastructural changes described, particularly those in companion cells.

The goal of this research was to determine whether crop management practices could substitute for a herbicide for managing mixed populations of green and yellow foxtail in hard red spring wheat. Crop yield and foxtail growth were measured in two years of field research in North Dakota. Spring wheat yields were as great or greater when early seeding date or 2× seeding rate were substituted for POST diclofop3 at 0.75 kg ai ha−1 for managing foxtail in spring wheat. Yield of spring wheat competing with foxtails was greater for the high seeding rate (2× = 270 kg ha−1) than both the normal (1× = 130 kg ha−1) and low (0.5× = 70 kg ha−1) seeding rates for early or middle seeding dates, but not for the late seeding date. For both early and middle seeding dates, wheat yield at the 2×seeding rate without diclofop was equal to or greater than that of the 1× seeding rate with diclofop. Late-seeded wheat did not yield well in competition with dense foxtail stands for any treatment combination. Early and middle seeding dates favored the relative increase of green foxtail over yellow foxtail in wheat, whereas late seeding favored yellow foxtail over green foxtail. Economic analysis demonstrated that early seeding date was the most critical factor in determining the stochastic dominance of treatments without diclofop over treatments with diclofop. Seeding rate was much less important than seeding date in determining the ranking of treatments in stochastic dominance analysis.

Two field experiments were conducted to examine the competitive effect of common cocklebur and sicklepod in soybean. Factors examined included sap flow of both the weed and the crop, as well as the traditional parameters of weed and crop growth and crop yield. The intent was to determine to what extent competitive effects could be attributed to differential water utilization. In the first study, soybean planted at 20 plants m−1 row was infested with either sicklepod at 10 plants m−1 row or common cocklebur at two plants m−1 row. Sicklepod reduced soybean sap flow and yield 53 and 49%, respectively. Common cocklebur reduced soybean sap flow and yield 31 and 38%, respectively. Within a weed species, weed-induced yield and sap flow reductions were comparable, indicating that water deprivation was the primary detriment that these weeds inflicted on soybean. Individual common cocklebur plants were 3.9 times more competitive than sicklepod with respect to reducing soybean yield. However, sap flow of individual common cocklebur plants was only 1.4 times more than that of sicklepod, indicating that water deprivation was not the only causal factor in weed-crop competition. In the second experiment, sicklepod was planted in soybean (fixed density) and clipped to either half the height, same height as soybean, or left unclipped, in an attempt to simulate herbicide-induced stunting. Clipping sicklepod had a positive effect on soybean sap flow and yield. Thus, the benefits of reduced weed competition were achieved without killing sicklepod.

Experiments were conducted to evaluate the occurrence and significance of release of herbicide through subterranean parts of nicosulfuron-treated johnsongrass. In a bioassay, the rooting medium of johnsongrass treated foliarly with 50 or 100 μg nicosulfuron plant−1 was inhibitory to the radicle elongation of sorghum and corn indicating the increased toxicity of the rooting medium of nicosulfuron-treated johnsongrass. The study with 14C-nicosulfuron indicated a basipetal translocation of foliarly applied nicosulfuron in johnsongrass to its roots/rhizomes and also into the rooting medium. By 30 DAT, around 23% of the 14C-label absorbed by johnsongrass was found exuded into the rooting medium. Radiochromatogram scans of thin layer chromatography plates of rooting medium indicated unmetabolized nicosulfuron as the major 14C-labeled compound (56%). The study also revealed a subsequent uptake of exuded 14C by corn roots sharing the medium. On the whole, the amount of 14C-label recovered from untreated corn amounted to 4.3% of the total applied to johnsongrass. In another experiment, the presence of nicosulfuron in the rooting medium was detrimental to corn growth. Reductions in corn growth occurred at concentrations of 10−8 M nicosulfuron or greater in the rooting medium. The sensitivity of corn to root uptake was attributed to greater accumulation of nicosulfuron at a faster rate in the growing parts.

Field horsetail shoots were severed from the rhizomes and grown hydroponically with and without shade (40 and 190 μmol m–2 s–1 photosynthetic photon flux) under six different nutrient regimes, by using nutrient solutions with different amounts of nitrogen (N) and potassium (K) (6/42 mmol L–1 N; 7/15/24 mmol L–1 K). Nutrients were supplied daily with the same volumes for the six different nutrient solutions at exponentially increasing rates corresponding to a maximum relative growth rate (RGR) of 12.5% from days 0 to 31 and 6% from days 32 to 48. RGR was calculated for the highest N and K rate. Photosynthetic rate and stomatal conductance to water vapor were determined on day 48, then the plants were harvested. The fresh weight (FW) and dry weight (DW) of different plant components were determined. Shade completely inhibited growth of tubers and fertile shoots and drastically reduced RGR, average aerial shoot height, and DW of shoots and rhizomes. N supplied at the high rate to unshaded plants increased the growth of all parts or the plant except fertile shoots and tubers. No effects of K were detected at the low N rate, whereas at the high N rate, K significantly increased total DW and belowsurface DW. RGR never exceeded 10% d–1. In the unshaded treatments, the K concentration was higher in aerial shoots, 150 to 240 μmol g–1 FW, than in belowsurface organs, 30 to 90 μmol g–1 FW. Shoot growth was significantly reduced at shoot K concentrations below 150 to 210 μmol g–1 FW, and root growth was significantly reduced at root K concentrations below 30 to 50 μmol g–1 FW. K significantly increased maximum net photosynthetic rate, 10 μmol CO2 m–2 s–1, at light saturation, 1,300 μmol m–2 s–1, in unshaded plants, whereas it reduced the light compensation point and respiratory losses of CO2 in darkness. It is concluded that field horsetail is a typical sunny habitat species with a rather high K demand.

The fact that quackgrass may occasionally escape control by the herbicide glyphosate is thought to result from the wide range in growth rate and sink activity among rhizome buds, especially in older portions of the rhizome. To study growth of rhizome structures, we supplied whole plants with 14CO2 throughout a 10-h light period and determined the amount of labeled carbon accumulated by the end of the subsequent 14-h night. Growth of rhizome structures during this 24-h period was estimated by determining their growth rate coefficients: the amount of labeled carbon accumulated per unit of carbon present in the structure. Growth rate coefficients generally were high for the rhizome tip that is enclosed in a sheath and the adjacent bud and rhizome segment, with values decreasing rapidly in a basipetal direction. However, extensive differences in the level and pattern of assimilate accumulation among rhizome structures were observed as rhizome development continued. Glyphosate accumulation generally paralleled the level of assimilate accumulation even though the range among rhizome structures for both increased with rhizome age. As a result of the increased variability among buds, some of the older buds will accumulate only a small, perhaps sublethal, amount of glyphosate and this may explain the tendency of the buds in older regions to escape control by glyphosate.

Field observations indicate that wheat (Triticum aestivum L.) is considerably more tolerant to soil residues of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} than barley (Hordeum vulgare L.). The basis for relative differences in tolerance was investigated by measuring herbicide dose response, uptake, movement, and metabolism using ‘Clark’ barley and ‘Marberg’ wheat. Barley root fresh and dry weights were significantly reduced when roots were exposed to nutrient solution containing 35 mM chlorsulfuron for 1 day. Wheat roots similarly exposed for 3 days to 1.1 mM chlorsulfuron displayed no growth reduction. The small differences in uptake and movement of chlorsulfuron detected in wheat and barley are inadequate to explain the large response difference between the two species. Both species rapidly metabolize chlorsulfuron in 1 day and there is no significant difference in the level of parent compound remaining in barley compared to wheat. A factor other than uptake, movement, or metabolism must account for barley roots greater sensitivity to root-applied chlorsulfuron.

The relationships between microorganisms and velvetleaf (Abutilon theophrasti Medic. # ABUTH) seeds in contact with soil were studied to determine microbial effects on velvetleaf seed viability. The characteristic seed microbial association persisted on velvetleaf seeds placed on the soil surface during 32 days of incubation. The fungal association comprised of Alternaria alternata (Fr.) Keissl., Cladosporium cladosporioides (Fres.) de Vries, Epicoccum purpurascens Ehrenb. ex Schlecht, and Fusarium spp. was detected on over 50% of the seeds during incubation. Establishment of soil microorganisms on 50% of seeds occurred at only one sampling date. Such establishment was largely unsuccessful due to the effective barrier presented by seedborne microorganisms. Seedborne and soilborne microorganisms were unable to reduce viability of velvetleaf seeds in contact with soil as the total viability of all seeds tested exceeded 90% during incubation. Velvetleaf seedborne microorganisms may augment seed longevity on and in soils by acting as a barrier to potential seed decomposers originating from soil.

The effects on leucine uptake and its incorporation into protein by cucumber (Cucumis sativus L. ‘Ashley’) cotyledon tissue following treatments with 2,4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne) were determined. Prometryne decreased 14C-leucine uptake both in the light and in the dark. Prometryne decreased leucine incorporation into protein only when the discs were also exposed to over 4 hr of light. Percent of absorbed leucine incorporated into protein was increased by a 4 hr exposure in the light to 10−4M prometryne following a 24-hr dark exposure to this same concentration. Similar exposure to 10~5M prometryne had no effect. Percent of leucine incorporated into protein was decreased by 10-5M prometryne following a 24 hr exposure to this same concentration in the light. However, under these conditions 10−4M prometryne had no effect. It is speculated that the increased percentage of leucine incorporated into protein may be related to increased availability of the absorbed leucine for use in protein synthesis rather than an effect of the herbicide on the rate of protein synthesis

The effects of imazaquin and imazethapyr on cotton planted the year following application to soybean were studied on one silt loam and two clay soils in Arkansas from 1989 to 1991. Imazaquin was applied to soybean at 0.07 kg ai ha−1 PPI and POST, 0.14 kg ha−1 PPI, PRE, and POST, and sequentially PPI or PRE followed by POST at 0.14 kg ha−1 per application. Imazethapyr was applied at 0.035 kg ha−1 PPI and POST, 0.07 kg ha−1 PPI, PRE, and POST, and sequentially PPI or PRE followed by POST at 0.07 kg ha−1 per application. Soil residues of 0.07 kg ha−1 imazaquin and imazethapyr did not injure cotton at any location. Residues of 0.14 kg ha−1 imazaquin applied sequentially reduced cotton shoot dry weight for 6 wk after emergence on clay but not on silt loam soil. The PPI followed by POST sequential imazaquin treatment (0.28 kg ha−1 total imazaquin) delayed initiation of fruiting and reduced yield and lint quality.

Early postemergence application of atrazine [2-chloro-4- (ethylamino)-6-(isopropylamino)-s-triazine] at 0.28 kg/ha in combination with alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 0.42 kg/ha plus a non-toxic oil-surfactant blend gave season-long weed control in sweet corn (Zea mays L. var. rugosa ‘Seneca Chief’). Bioassay with oats (Avena sativa L.) showed no detectable atrazine residue in the soil 3 months after herbicide application. In greenhouse studies, the response of Japanese millet (Echinochloa crus-galli L. Beauv. var. frumentacea) to early postemergence application of atrazine and alachlor combinations plus an oil-surfactant blend was synergistic. Soil uptake played a major role in the activity of the herbicides. Formulants used in commercial alachlor when added to atrazine spray, enhanced atrazine activity in a way similar to that of the non-toxic oil-surfactant.

Visible wheat (Triticum aestivum L.) injury, delay in bloom date, and yield reduction were observed following herbicide treatments in growing wheat. Protein content and volume weight of winter wheat were not significantly affected by any herbicide treatment. Some treatments reduced annual grass and broadleaf population by 90% or more 6 weeks after spraying and maintained weed control 8 weeks in untilled winter wheat stubble. Effective herbicide treatments that caused the least winter wheat injury in 1977 and 1978 included metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one] + alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 0.3 + 2.8 kg/ha, metribuzin + oryzalin (3,5-dinitro-N 4,N 4-dipropylsufanilamide) at 0.3 + 1.8 kg/ha, metribuzin + pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] at 0.3 + 2.2 kg/ha, metribuzin + SN-533 [N-ethyl-N-propyl-3-(propylsulfonyl)-1H-1,2,4-triazole-1-carboxamide] at 0.3 + 0.8 kg/ha, and R-40244 [1-m-trifluoromethylphenyl)-3-chloro-4-chloromethyl-2-pyrrolidone] at 1.1 kg/ha. Herbicide treatments that showed the most potential to control annual grass and broadleaf weeds selectively in tillered winter wheat and stubble in 1978 include metribuzin + metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 0.3 + 2 kg/ha, metribuzin + oryzalin at 0.3 + 1.4 kg/ha, and metribuzin + pendimethalin at 0.3 + 2 kg/ha.

EPTC (S-ethyl dipropylthiocarbamate), benefin (N-butyl-N-ethyl-α α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine], butralin[4-(1,1-dimethylethyl)-N-(1-methylpropyl)2,6-dinitrobenzenamine], diclofopmethyl {methyl 2-[4-(2,4-dichlorophenoxy)phenoxy]-propanoate} and 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] were evaluated in the greenhouse for effects on growth, nodulation, and NH3 production of alfalfa (Medicago sativa L.) and medium red clover (Trifolium pratense L.). Some reduction in nodulation occurred from some rates of the herbicides, but reduction in nodulation was usually associated with reduced plant growth caused by herbicidal injury.

Greenhouse experiments were conducted to evaluate phytotoxicity, absorption, and translocation of thifensulfuron when applied to pea at different rates, droplet sizes, and as dry particles. Thifensulfuron rates that reduced shoot dry weight by 25% were 0.46, 0.59, 0.98, and 1.21 g ai ha-1 for droplet diameters of 110, 155, 300, and 450 μm, respectively. The 14C-thifensulfuron absorption as percent of applied increased twofold, whereas translocation decreased 36% as herbicide concentration increased from 18 to 146 mg L-1 in 980-μm droplets. Small droplets (50 μm) that dried to particles before contact with leaves did not damage pea plants. However, under dew conditions, dry particles damaged peas to a similar degree as liquid droplets. We concluded that small and concentrated droplets of thifensulfuron can damage peas more than large and diluted droplets as a result of increased herbicide absorption.

Solutions containing 3-(m-trifluromethylphenyl)-l,l-di-methylurea (fluometuron) or 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron) were displaced through saturated 250-μ glass beads or through Norge loam soil at two water flow rates. The procedure used allowed uniform application of herbicide solutions to the soil surface and subsequent displacement of the herbicide through soil or glass bead columns at a constant water flow rate. Fluometuron was as mobile as the chloride ion at both high and low flow rates. The shape of the fluometuron distribution curves obtained at the two flow rates were distinctly different. The volume of water required to displace fluometuron through a material that adsorbed the herbicide was greater than that necessary to displace the fluometuron through materials giving a smaller amount of adsorption. More diuron was adsorbed by the glass bead system than fluometuron.