Field studies were conducted to measure the response of corn (Zea mays L. var. ‘Pioneer 3377’) to foliar applications of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid}, and haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid} as influenced by corn growth stage and the addition of 7.7, 15,4, 77.7, 140, 280, and 840 g/ai/ha of bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. Applications of sethoxydim (16.8, 33.6, 67.2, 100, and 134 g ai/ha), fluazifop, or haloxyfop (1.0, 2.0, 4.0, 8.0, 10.0, and 13.4 g ai/ha) to four- to five-leaf corn did not reduce seed weight, but significant reductions resulted when sethoxydim (100 g/ha) or fluazifop (13.4 g/ha) was applied to 70- to 80-cm (six-leaf) corn with or without bentazon. Corn grain yield was significantly reduced by sethoxydim (>67.2 g/ha) treatment at either growth stage of corn. In contrast, corn injury induced by fluazifop (>8.0 g/ha) and haloxyfop (13.4 g/ha) resulted in reductions in yield only when applications were made to 70- to 80-cm corn. Significant reductions in seed germination also resulted from foliar applications of the graminicides, but these reductions were inconsistent across corn growth stage.

Translocation of 14C-haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} in quackgrass [Agropyron repens (L.) Beauv. # AGRRE] from the treated area (the middle 2.5 cm of the second of three leaves) to the lower leaves was reduced in plants in which 0.56 kg/ha of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} or bentazon [3-1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide] was added in tank mixture to a 0.07 kg ai/ha application of haloxyfop. Reduced translocation did not occur when haloxyfop rates were increased to 0.28 and 1.1 kg/ha. Bentazon reduced absorption of 14C-DPX-Y6202 {2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propionic acid} when applied in tank mixtures with 0.28 and 1.1 kg ai/ha DPX-Y6202. There was less 14C-DPX-Y6202 in the leaf tips of plants treated with 0.07 kg/ha DPX-Y6202 plus 0.56 kg/ha acifluorfen in tank mixture. Relatively small amounts of both 14C-haloxyfop and DPX-Y6202 accumulated in the rhizome and adjacent shoots and acifluorfen did not influence translocation to these plant parts. Considerably more 14C-haloxyfop than 14C-DPX-Y6202 was absorbed by quackgrass. Treatment of quackgrass with acifluorfen or bentazon 24 h prior to application of 14C-haloxyfop or 14C-DPX-Y6202 did not influence absorption or translocation.

The influence of some s-triazine herbicides on acid phosphatase (acid Pase) and phosphodiesterase (PDase) from corn (Zea mays L. var. ‘Orfeo’) roots was investigated. Terbutryn [N-(1,1-dimethylethyl)-N′-ethyl-6-(methylthio)-1,3,5-triazine-2,4-diamine] stimulated both phosphatases, whereas prometryn [N,N′-bis(1-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine] stimulated only the PDase. Atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and desmetryn [N-methyl-N′-(1-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine] inhibited both phosphatases to varying degrees. Atraton [N-ethyl-6-methoxy-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], prometon [6-methoxy-N,N′-bis(1-methylethyl)-1,3,5-triazine-2,4-diamine], and simazine (6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine) inhibited acid Pase. No effect was exerted by ametryn [N-ethyl-N′-(1-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine]. The enzyme assays and the kinetic parameters demonstrated that the interferences observed were due to an action on the synthesis of one or both enzymes rather than on the enzyme reactions. The types of the N-alkyl and the C1-substituent groups in the structures of the s-triazines tested appear important in determining the degree of the interference.

Four synthetic multiring analogs of strigol (0.1 mM) were effective as germination stimulants of dormant, unchilled seeds of shepherdspurse (Capsella bursa-pastoris (L.) Medik. # CAPBP). The effect was concentration dependent and exceeded that produced by 0.1 mM gibberellic acid (GA). The analog treatments resulted in normal, unpigmented seedlings after 7 days, whereas GA treatment led to distorted, nongeotropic, yellow seedlings. The strigol analogs were also more effective in inducing shepherdspurse germination than 10 mM nitrate or 5.0 mM thiourea (ineffective in the dark) and 5.0 mM thiourea plus 4.5 mM ascorbate (germination stimulated, but seedling growth, inhibited). Chilling at 4 C for 11 days reduced the effectiveness of the strigol analogs, but not that of gibberellic acid and thiourea plus ascorbate. Ascorbate acts synergistically with thiourea in promoting shepherdspurse germination. Strigol and epistrigol had no effect on either chilled or unchilled shepherdspurse seeds. The stimulation of dormant shepherdspurse seeds by the synthetic strigol analogs is the first demonstration that these compounds have bioregulatory activity in dormant seeds of genera other than Striga.

Root and foliar absorption and translocation of 14C-metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] were determined in tolerant (‘Steptoe’) and susceptible (‘Morex’) barley (Hordeum vulgare L.) cultivars grown in nutrient solution culture under greenhouse conditions. Root-applied metribuzin toxicity to the two barley cultivars was also examined. A 50% reduction in growth occurred at 0.22 and 0.72 μM metribuzin for Morex and Steptoe, respectively. Root absorption was similar for both cultivars at 1 day, but Steptoe absorbed about two times more metribuzin 4 and 8 days after application than did Morex. Steptoe absorbed 19% of the total applied metribuzin by 8 days. Root absorption was positively correlated with water uptake (r≥ 0.87). Leaf absorption was three times greater for Morex than for Steptoe after 4 days. Transport to leaves from root application was rapid, and, by 1 and 8 days, leaves of Steptoe contained 71 and 82% and leaves of Morex 78 and 84% of the total absorbed 14C, respectively. Translocation was apoplastic following both root and leaf absorption and was similar for both cultivars. Differential tolerance could partially be accounted for by differences in foliar absorption but not by differences in root absorption.

Experiments were conducted to determine 14C absorption and translocation by oat (Avena sativa L. ‘Lyon’) foliarly treated with 14C-sethoxydim {(2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one)} and various additives. Safflower (Carthamus tinctorius L.), soybean [Glycine max (L.) Merr.], linseed (Linum usitatissimum L.), and sunflower (Helianthus annuus L.) oil all similarly increased foliar absorption and translocation of 14C more than palm oil (Elaeis quineensis Jacq.) but less than petroleum oil, when applied without an emulsifier. An emulsifier in the oil additive tended to enhance 14C absorption and translocation more in soybean oil than petroleum oil so that 14C absorption and translocation were similar with both oils containing emulsifiers. Absorption and translocation of 14C tended to increase more with an increase in emulsifier concentration in soybean oil than in petroleum oil but not beyond 15% with either oil. Percentage of 14C absorbed and translocated from 14C-sethoxydim applied to oats increased as the amount of soybean oil applied increased from 2.3 to 4.6 L/ha, but the increase was less for sethoxydim at 0.87 kg ai/ha than at 0.03 or 0.17 kg ai/ha.

Various populations of common lambsquarters (Chenopodium album L. # CHEAL) and late-flowering goosefoot (Chenopodium strictum Roth. # CHESG) plants were studied at the eight-to ten-leaf stage. Prior to measurement of fluorescence induction, the detached leaves were vacuum infiltrated with unformulated atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea], and pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone]. The fluorescence induction measurements were then made 1 h after adaptation in the dark. The fluorescence induction curves of intact leaves were recorded with a laboratorybuilt apparatus. A xenon lamp was used to produce the actinic beam. Cytological tests were done on meristematic cells of the root tips of the seedlings treated in 2 nM 8-hydroxyquinoline. The cytotypes were hexaploids (among which were atrazine-susceptible, pyrazon-susceptible, atrazine-resistant, and pyrazon-tolerant populations), and tetraploids (among which were atrazine-susceptible and atrazine-tolerant populations).

The ether extract of small everlasting (Antennaria microphylla Rydb.) was phytotoxic to lettuce seed root growth and leafy spurge (Euphorbia esula L. # EPHES) root elongation and cell culture growth. Three phenolic compounds (hydroquinone, arbutin, and caffeic acid) were chromatographically isolated and characterized from the ether extract. Arbutin and caffeic acid were moderately phytotoxic to leafy spurge root growth at 300 ppm (w/v), and hydroquinone was strongly phytotoxic to leafy spurge root growth at 50 ppm (w/v). The observed phytotoxicity of hydroquinone and the high-yield natural occurrence of arbutin, a water soluble, easily hydrolyzed monoglucoside of hydroquinone, in small everlasting is consistent with the participation of these two compounds in the observed allelopathy of small everlasting against leafy spurge.

Absorption and translocation of glyphosate [N-(phosphonomethyl)glycine] with and without adjuvants were examined in field bindweed (Convolvulus arvensis L. # CONAR) to develop an understanding of the influence of selected adjuvants and environment before application on glyphosate activity. Light intensity and humidity during plant development resulted in differences in 14C-glyphosate absorption. When applied in water or with an oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate) adjuvant, an average of 9% of the glyphosate was absorbed in plants grown in high light intensity, low humidity (HLLH) before treatment, compared to an average of 21% in plants grown in low light, high humidity (LLHH) before treatment, respectively. Amounts of epicuticular wax on HLLH field bindweed were almost three times as great as on LLHH leaves and may explain absorption differences. No differences in glyphosate absorption were observed between glyphosate applied with oxysorbic or no adjuvant even though the oxysorbic adjuvant effectively reduces surface tension. Absorption was increased two- to threefold with a polyethoxylated tallow amine adjuvant (MON 0818) compared to no adjuvant. Unlike absorption without adjuvant or with oxysorbic adjuvant, there were few absorption differences in plants grown in different environments before application. Absorption continued for 24 to 36 h after application regardless of adjuvant. Reductions in MON 0818 concentration and subsequent necrosis resulted in increased movement of radioactivity away from the site of application.

Rush skeletonweed (Chondrilla juncea L. CHOJU) infestations occur along the eastern seaboard and in several western states of the United States. This Eurasian species was inadvertently introduced prior to 1870, with established stands first reported in Maryland and West Virginia (16). These infestations (16) were assessed as lacking aggressive characteristics and posed little threat as a problem weed. Although rush skeletonweed was discovered in the Pacific Northwest as early as 1938, the species was not recognized as a potential weed problem until nearly three decades later (27). Subsequent surveys revealed that infestations occupied over 2.3 million ha in California, Idaho, Oregon, and Washington (6). Attempts to generate support for an organized control program in Idaho were met with little enthusiasm during the 1960's.

Two strains of crownvetch (Coronilla varia L. # CZRVA) rhizobia were cultured in vitro with various rates of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate]. Growth, measured turbidimetrically over 48 h, was similar for both strains. Atrazine and bifenox significantly reduced bacterial growth after 14 and 36 h, respectively, only at the highest concentrations tested (463 μM atrazine and 292 μM bifenox). Since growth of crownvetch rhizobia was apparently not affected by rates of atrazine or bifenox above reasonable soil solution concentrations, it is likely that herbicidal effects on nodulation were due to toxicity to the host plant rather than toxicity to these bacteria. In a growth chamber experiment, total nodule activity (TNA) and carbon dioxide exchange rate (CER) were measured simultaneously in an effort to distinguish direct atrazine effects on nodule function from indirect effects due to inhibition of photosynthesis and a resulting decrease in photosynthate supply to nodules. When 5 and 50 mg atrazine per kg soil were applied to intact plants, CER was severely reduced within 24 h, but similar reductions in TNA were not observed until 48 h after treatment. Total nodule activity was reduced similarly by atrazine and defoliation; the application of atrazine to defoliated plants did not inhibit TNA more than did defoliation alone. The data indicate that reductions in crownvetch nodule activity by atrazine are due to inhibition of photosynthesis or other processes rather than direct toxicity to N fixation.

To investigate the mode of action of a grass-specific herbicide, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} was added to corn and soybean cell suspension cultures containing metabolic intermediates such as sucrose [14C-U], sodium acetate [14C-1,2], or L-leucine [14C-U]. Death of the corn suspension cells occurred within 3 days after haloxyfop was added at a concentration of 1.0 μM to supplemented Murashige and Skoog's medium. At 0.1 μM haloxyfop, 14C-sucrose uptake and 14C loss due to respiration of the corn cells declined without a significant reduction in cell fresh weight, cell viability, cellular ATP level, free sugar content, cell wall materials, or level of glycolytic intermediates. The proportions of sucrose, glucose, and fructose in the free sugar fraction were not affected. However, the 14C-labeled free amino acid level was increased. During a 24-h incubation period, incorporation of leucine [14C] as a precursor revealed that haloxyfop did not inhibit protein synthesis. Incorporation of acetate [14C-1,2] showed that total lipid synthesis was inhibited by 42% at 0.1 μM haloxyfop (sublethal). Similar responses were observed in the soybean suspension cells; however, the calculated 50% lethal concentration (LC50) was 47 times higher than for corn cells. The results of this study suggest that the site of action of haloxyfop is located where metabolic intermediates enter the Kreb's cycle and lipid synthesis. Glycolysis is not inhibited.

Previous research has shown that haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} and sethoxydim {2-[1-(ethoxyimino)butyl-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} give less control of quackgrass [Agropyron repens (L.) Beauv. # AGRRE] when applied at the five- to seven-leaf stage compared to the three- to four-leaf stage. Current research indicates that reduced control of quackgrass in the eight-leaf stage, compared to the four-leaf stage, was not due to reduced herbicide retention on leaves or to changes in residual herbicide activity in the soil following postemergence applications. The efficacy of both herbicides on rhizome bud kill did not change between the four- and eight-leaf stages following application to the foliage. However, the efficacy of both herbicides on crown tissue bud viability was less at the eight-leaf stage. Rhizome sink intensity (the capacity to accumulate radiolabel) was similar at both stages of development following 14C-haloxyfop and 14C-sethoxydim application to either upper or lower leaves. Crown tissue sink intensity was significantly less at the eight-leaf stage compared to the four-leaf stage following 14C-sethoxydim application to either upper or lower leaves and following 14C-haloxyfop application to lower leaves. These data suggest that crown bud regrowth contributes substantially to reduced control of quackgrass in advanced stages of growth following applications of haloxyfop and sethoxydim.

To develop an understanding of how adjuvants might enhance glyphosate [N-(phosphonomethyl)glycine] activity, absorption and translocation of a polyethoxylated tallow amine amphoteric surfactant (MON 0818) were examined in field bindweed (Convolvulus arvensis L. # CONAR). Scanning electron microscopy did not reveal any physical disruption of the epicuticular waxes from spray applications of MON 0818, an oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate) surfactant, or glyphosate. Radioactive MON 0818 absorption was rapid during the first 6 h. Maximum absorption (84%) occurred by 24 h after application. Less than 3% of the applied radioactivity was recovered from the epicuticular wax of treated leaves. Movement of radioactivity away from the treated area was limited predominantly to movement within the treated leaf. Altering light intensity or humidity in which the plants developed before treatment did not influence MON 0818 absorption.

The cross-resistance of triazine-resistant biotypes of smooth pigweed (Amaranthus hybridus L. # AMACH), common lambsquarters (Chenopodium album L. # CHEAL), common groundsel (Senecio vulgaris L. # SENVU), and the crop canola (Brassica napus L. var. Atratower) to a selection of herbicides was evaluated at both the whole plant and chloroplast level. The triazine-resistant biotypes of all four species showed a similar pattern of cross-resistance, suggesting that a similar mutation had occurred in each species. The four triazine-resistant biotypes were resistant to injury from atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], bromacil [5-bromo-6-methyl-3-(1-methylpropyl)-2,4-(1H,3H)pyrimidinedione], and pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone] and were slightly resistant to buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone}. The triazine-resistant biotypes were more sensitive to dinoseb [2-(1-methylpropyl)-4,6-dinitrophenol]. Triazine-resistant smooth pigweed showed resistance to cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile} and metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] with slight resistance to linuron [N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea] and desmedipham {ethyl [3-[[(phenylamino)carbony] oxy] phenyl] carbamate}. There was little or no resistance to diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea], bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], or dicamba (3,6-dichloro-2-methoxybenzoic acid). Parallel studies at the chloroplast level indicated that the degree of resistance to inhibition of photosynthetic electron transport was highly correlated with the degree of resistance to herbicidal injury. This correlation indicates that atrazine, cyanazine, metribuzin, pyrazon, bromacil, linuron, desmedipham, and buthidazole cause plant injury by inhibition of photosynthesis. This correlation also indicates that triazine resistance and cross-resistance at the whole plant level is due to decreased sensitivity at the level of photosynthetic electron transport. Cross-resistance to numerous additional herbicides was evaluated on isolated chloroplast thylakoid membranes and these results are discussed. 14C-atrazine was displaced from thylakoid membranes by several herbicides, indicating that these herbicides compete for a common binding site.

Three triazine-resistant biotypes of grass weeds, hood canarygrass (Phalaris paradoxa L. # PHAPA), ryegrass (Lolium rigidum Gaud.), and slender foxtail (Alopecurus myosuroides Huds. # ALOMY) were collected along roadsides on the coastal plain of Israel that had been treated repeatedly with s-triazine herbicides. Resistant biotypes (R) survived up to 4 kg ai/ha of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] applied pre-and postemergence, while susceptible (S) biotypes were killed by 0.25 kg/ha. R and S biotypes were equally sensitive to diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea]. Electron transport in chloroplasts isolated from R biotypes was not affected by atrazine, whereas in S biotypes electron transport was inhibited 50% by 0.4 to 1.0 μM atrazine. Chloroplasts from both biotypes were equally sensitive to diuron. These data indicate that the R biotypes have a plastidic mode of resistance to atrazine. In addition, seedlings of R biotypes exhibited resistance to triazinone herbicides. The R biotype of hood canarygrass was more tolerant to postemergence application of diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}.

Four Centaurea species, diffuse knapweed (C. diffusa Lam. # CENDI, spotted knapweed (C. maculosa Lam. # CENMA), yellow starthistle (C. solstitatilis L. # CENSO), and the closely related Russian knapweed [Acroptilon repens (L.) DC. syn. Centaurea repens L. # CENRE] are serious introduced weeds which infest extensive areas of pasture and rangeland in Canada and the United States (1, 10, 14, 17, 18, 26, 30). Russian knapweed and yellow starthistle are also troublesome in cultivated land (1, 14, 26). These four species are members of the Cardueae tribe of the Asteraceae family and have been accidentally introduced from Eurasia as contaminants in crop seed.

Tridiphane [2-(3,5-dichlorophenyl)-2-(2,2,2-trichloroethyl)oxirane] inhibited growth of seedling corn (Zea mays L. ‘DK T 1100’), wheat (Triticum aesetivum L. ‘Arthur’), and sorghum (Sorghum vulgare Pers. ‘DK 42Y’) in growth chamber experiments. These inhibitions were partially circumvented by simultaneous treatment with OTC (L-2-oxothiazolidine-4-carboxylic acid). Tridiphane, atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], and OTC each increased levels of low molecular weight thiols (glutathione) in intact roots of treated corn seedlings, but only OTC did in excised roots. Tridiphane and atrazine caused a decrease in thiol content of excised roots. Tridiphane treatments reduced the amount of glutathione S-transferase activity extractable from corn roots, and this reduction was circumvented partially by OTC applied in combination with tridiphane. These data present evidence that tridiphane interference with cysteine or glutathione metabolism can be reversed by increasing cellular content of cysteine.

Absorption and translocation of 14C-ethalfluralin (N-ethyl-N-(2-methyl-2-propenyl)-2,6-dinitro-4-(trifluoromethyl)benzenamine) were measured in cucumber plants in the field and greenhouse. In field enclosures, cucumbers treated with 1.68 or 3.36 kg ai/ha preemergence soil-surface applications of 14C-ethalfluralin accumulated significantly more 14C in leaves than in petioles, stems, or fruits. In greenhouse studies, 14C-ethalfluralin vapor was absorbed by both cucumber seedling stems and cotyledons. Seedlings absorbed 14C-ethalfluralin from a nutrient solution and translocated 14C into all plant parts. Cucumber absorbed 14C-ethalfluralin topically applied to the stem and translocated 14C acropetally, while only limited basipetal translocation occurred. Although cotyledons absorbed 14C-ethalfluralin, very little 14 C moved out of the treated tissue.