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.

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.

Effects of ethylene and KNO3 on the germination of dormant common lambsquarters (Chenopodium album L. # CHEAL) seed were studied under controlled environmental conditions. Ethylene, applied in the gaseous form or as an aqueous solution of ethephon (2-chloroethylphosphonic acid), was able to overcome the dormancy of over 70% of the seed. The optimum concentrations of ethylene and ethephon were 10 μL·L-1 and 100 mg·L-1, respectively. The dormancy-breaking action of ethylene was dependent on the availability of nitrate. Hence, seed containing a high level of endogenous nitrate responded readily to ethylene, whereas nitrate-deficient seed required a combined application of ethylene and nitrate. Stimulation of seed germination by ethylene was observed in soil at all depths studied (up to 15 cm). The sensitivity of seed to ethylene increased upon imbibition to reach a peak on the third day, followed by a steady decline. Consequently, the greatest promotion of germination occurred when ethylene was administered during the first 3 to 4 days of imbibition. The loss of seed sensitivity was neither preempted nor overcome by an exogenous supply of KNO3, and may imply that the seed had passed into secondary dormancy. The present findings could form the basis for the use of ethylene to accomplish commercially significant promotion of germination in the field and thus improve the efficiency of the control of common lambsquarters.

Phytotoxicity of chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide} in cell cultures of Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] was approximately 30-fold greater than in leafy spurge (Euphorbia esula L. # EPHES) cultures. Differences in chlorsulfuron phytotoxicity in these two species were attributed to large differences in cellular metabolism of the herbicide. Leafy spurge cells metabolized all of the applied 14C-chlorsulfuron within 72 h of treatment, while Canada thistle metabolized less than 2%. Acid hydrolysis of the metabolic products isolated from leaf disks and cell cultures of leafy spurge yielded a radioactive product that cochromatographed with a 2-chlorobenzenesulfonamide standard. Therefore, metabolic transformation occurred on the heterocyclic portion of the molecule. A major metabolite was further characterized as 2-chloro-N-[[4-(hydroxymethyl)-6-methoxy-1,3,5-triazin-2-yl]aminocarbonyl]-benzenesulfonamide by cochromatography with the authentic standard.

Horse purslane (Trianthema portulacastrum L. # TRTPO) seeds germinated from 20 to 45 C. Maximum germination of 90% was observed at 35 C. Germination was highest between the 4th and 8th days of incubation. Horse purslane seeds did not exhibit dormancy. Freshly harvested seeds when incubated at 35 C germinated to the extent of 54 to 56%. Seed germination steadily increased up to 7 and 8 months when stored under laboratory and field conditions, respectively. Seeds stored in soil had significantly higher germination than those stored in the laboratory. Maximum seedling emergence resulted when seeds were planted at 1 cm and gradually declined with the increased seeding depth. Seeds lying on the surface gave very poor seedling emergence.

The effect of environmental conditions on horse purslane (Trianthema portulacastrum L. # TRTPO) emergence, growth, and reproduction was studied by sowing seeds on June 10, June 30, July 20, August 10, and August 30, 1984. The first three seeding dates resulted in significantly higher seedling emergence than the August 30 date. Leaf number, leaf area, dry matter, and number of branches per plant at the peak growth stages of this weed were significantly higher for the July 20 sowing than for the other sowing dates, followed closely by the June 30 sowing. Similarly, number of nodes per plant, seeds per plant, and seed weight per plant were also significantly higher for the July 20 sowing, followed closely by the June 30 sowing. Phenological behavior of the plants indicate that: a) maximum seedling emergence takes place during June and July, b) rapid and vigorous growth occurs during July and August (rainy season) when conditions for growth are optimum, and c) production of flowers and seeds starts 20 to 30 days after sowing.

Methyl isothiocyanate (MIT) consistently killed large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] seed at concentations of 4.0 mM or greater. Concentrations of 0.6 to 1.0 mM MIT delayed germination of large crabgrass seed but ultimately allowed the majority of seed to germinate. Dormant large crabgrass seed were killed at concentrations of MIT similar to those required to kill nondormant seed. MIT stimulated germination of dormant large crabgrass seed at sublethal concentrations (0.1 to 1.0 mM). Experiments with metham (sodium methyldithiocarbamate) in the greenhouse and field (metham rapidly degrades to MIT in soils) confirmed results of laboratory experiments with MIT.

Seed from 21 common milkweed (Asclepias syriaca L. # ASCSY) populations from six states were germinated on six substrates (filter paper, sand, peat, clay, and mixtures) under three temperature regimes. The variation in germination response between populations and experimental conditions was analyzed. The greatest percent germination (59% average over all substrates) was obtained with an alternating 20 C (16 h), 30 C (8 h) temperature regime. At a constant temperature of 30 C, germination was lower (32% average) and much more variable among seeds from different populations. At 25 C, average percent germination dropped to 1.2% over all substrates. Germination appeared to be strongly correlated with seed source (population), temperature, and substrate type, and poorly correlated with seed size. No association was found between geographical origin and germination response.

Phenolic content, germination percentage, and host preference were compared among 11 seed populations of witchweed (Striga hermonthica (Del.) Benth. # STRHE). Significant differences in germination percentage occurred among the seed populations after preconditioning by their exposure to different durations of warm-moist conditions. Greatest percentage of seed germinated after 8 days of preconditioning. Preconditioning for more than 16 days reduced percentage germination. The host specificity range of witchweed seed populations that parasitized pearl millet [Pennisetum americanum (L.) K. Schum] was broader than were those seed populations that attacked sorghum [Sorghum bicolor (L.) Moench.]. Results of thin-layer chromatography indicated large variations in phenolic content among the witchweed seed populations.

Seedlings from golden delicious apples (Malus domestica Borkh. ‘Smoothee’) were grown in the greenhouse with orchardgrass (Dactylis glomerata L. # DACGL), Kentucky bluegrass (Poa pratensis L. # POAPR), red sorrel (Rumex acetosella L. # RUMAA), and Korean lespedeza (Lespedeza stipulacea L. # LESSL) at four densities and four fertility levels. Orchardgrass and red sorrel inhibited tree growth more than Kentucky bluegrass on a per plant basis. Korean lespedeza inhibition of apple growth was associated with the amount of root nodulation on the Korean lespedeza. Apple shoot dry weight over all fertility levels, ground cover species, and densities was predicted by a regression model based on increase with fertility and decrease with ground cover dry weight. These results indicate that the competitiveness between equal number of ground cover species is due to differences in biomass production. Addition of nitrogen to the system increased nitrogen levels in apples but did not completely overcome apple growth inhibition.

The importance of seeds in the reproduction and maintenance of yellow nutsedge (Cyperus esculentus L. # CYPES) populations was evaluated. Isozyme analysis using starch gel electrophoresis was performed on 20 individuals of each of 10 widely separate populations in California. Genetic variation among individuals served as an indicator of the relative importance of asexual and sexual reproduction in each population. Eight enzyme systems were assayed from which 12 loci were resolvable, with four of those loci exhibiting variability. A maximum of four isozyme genotypes appeared in any population; only nine of 81 total potential genotypes were identified. Five populations were isozymically uniform, apparently composed of a single genotype. The remaining five populations were genotypically variable; these frequently deviated strongly from the genotype frequencies expected of a sexually reproducing population. These results indicate that sexually produced seeds are unimportant in the maintenance of yellow nutsedge populations in agricultural environments. Although viable seed may be produced, tubers appear to be the primary mode of reproduction in this species.

Field experiments were conducted to study the phenology and growth of broadbean (Vicia faba L. ‘Alameda’) and crenate broomrape (Orobanche crenata Forsk. # ORACR) in relation to planting date. The establishment of crenate broomrape on broadbean planted between mid-December and mid-January coincided with the flower initiation on the crop. Establishment occurred during the vegetative phase, several weeks before flowering from a mid-November and mid-October planting. In general, no consistent relationships were observed between growth of the host and attachment or subsequent growth stage of the parasite. The maximum number of crenate broomrape plants successfully attached to the host as well as the duration of the underground stage of crenate broomrape decreased as broadbean planting was delayed. Broadbean dry weight decreased as infection rate increased. This effect was more intense in early than late plantings.

Thirty-eight percent of monoecious hydrilla [Hydrilla verticillata (L.f.) Royle # HYLLI] grown from tubers produced new tubers after 28 days exposure to a 10-h photoperiod. One hundred percent of the plants grown at a 10-h photoperiod produced tubers by 56 days while only thirty-eight percent of those grown at a 12-h photoperiod did so. Plants grown at 14- or 16-h photoperiods did not produce tubers. Tubers appeared to be produced at the expense of new root and shoot tissue. Dioecious hydrilla (female) grown under similar conditions did not produce tubers by 56 days at any photoperiod examined. Relative growth rates (total dry weight) for both types did not differ with photoperiod and ranged between 81 ± 63 and 284 ± 52 mg·g-1·wk-1 (regression coefficient ± standard error; n = 30). In general, total chlorophyll (a+b) was greater for dioecious than for monoecious plants. The ratios of chlorophyll “a” to chlorophyll “b” and carotenoids to chlorophyll a changed with increasing photoperiod and plant age in a similar manner for both monoecious and dioecious plants.

Experiments were conducted to investigate enhanced biodegradation of carbamothioates and to evaluate the effect of microbial inhibitors on the efficacy of butylate [S-ethyl bis(2-methylpropyl)carbamothioate], EPTC (S-ethyl dipropylcarbamothioate), and vernolate (S-propyl dipropylcarbamothioate) in soils that had received butylate treatment in previous years (butylate-history soils). Inhibitors used were fonofos (O-ethyl-S-phenylether phosphonodithioate) and R-33865 (O,O-diethyl-O-phenylphosphorothioate). R-33865 and fonofos significantly improved control of large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] with butylate and EPTC in corn (Zea mays L. ‘Coker 21’). Bioassay data reflected more residual phytotoxicity from butylate and EPTC when these herbicides were combined with the microbial inhibitors. In butylate-history soils planted to soybeans [Glycine max (L.) Merr. ‘Wright’], R-33865 did not improve the efficacy of vernolate. These results indicated some cross-adaptation of the butylate-adapted microorganisms for EPTC, but no cross-adaptation was detected for vernolate. Under laboratory conditions, 14C-butylate was degraded more rapidly to 14CO2 in butylate-history soils than in non-butylate-history soils.

Absorption and translocation of 14C following 14C-fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} butyl ester and 14C-sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} application to oats (Avena sativa L. ‘Lyon’) was greater when the herbicides were applied with oleic acid, linoleic acid, or fatty acid methyl esters compared to various triglycerides. The methyl esters of stearic, oleic, linoleic, and linolenic acids enhanced 14C absorption and translocation when applied with 14C-fluazifop and 14C-sethoxydim, except that the methyl ester of stearic acid did not enhance 14C absorption and translocation when applied with 14C-sethoxydim. The absorption and translocation of 14C following the application of 14C-CGA-82725 {(±)-2-[4-(3,5-dichloro-2-pyridyloxy)phenoxy] propanoic acid)-2-propynylester}, 14C-diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, 14C-fluazifop, and 14C-sethoxydim were generally enhanced equally or greater by the methyl ester of sunflower (Helianthus annum L.) oil than by petroleum oil additive or once refined sunflower oil. Methylated sunflower oil was equally or more effective as an additive than petroleum oil in enhancing grass control with fluazifop and sethoxydim in a field experiment.

Diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl) glycine] applied posttransplant in peppers (Capsicum annuum L.) but preemergence to hairy galinsoga [Galinsoga ciliata (Raf.) Blake # GASCI] controlled the weed at 1.7 to 2.2 kg ai/ha. No serious crop injury or yield reduction was observed when diethatyl was applied to peppers at 9 kg/ha posttransplant or at bloom. Soil ridging, practiced to improve drainage and control the crown rot phase of Phytophthora blight (Phytophthora capsici L.), limited the duration of weed control by disrupting the herbicide-treated surface soil and exposing untreated soil. Diethatyl applied at 2.2 kg/ha posttransplant and again at pepper bloom, after the soil ridges were formed, controlled hairy galinsoga throughout the entire growing and harvest season.

The influence of various additives on the absorption and translocation of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} butyl ester in oats (Avena sativa L. var. ‘Lyon’) was determined. Fluazifop absorption and translocation by oats 48 h after application were less when applied with safflower (Carthamus tinctorius L.), sunflower (Helianthus annuus L.), soybean [Glycine max (L.) Merr.], linseed (Linum usitatissimum L.), and palm (Eleais quineeneis Jacq.) oil than with petroleum oil. However, fluazifop absorption and translocation continued to increase for the 96-h duration of the experiment when applied with soybean oil but only for 24 h when applied with petroleum oil. The 14C-fluazifop-label recovery was higher when applied with oils than when applied alone, which may have been due to reduced fluazifop volatility when it was emulsified with the oils. Absorption and translocation of fluazifop applied with glycerol or various emulsifiers were equal to or less than fluazifop absorption and translocation when applied with petroleum oils but were greater than fluazifop absorption and translocation when applied with seed oils 48 h after application. Fluazifop absorption and translocation were similar whether soybean or petroleum oil additives were applied with or without emulsifiers. Totally refined seed oils only slightly increased fluazifop absorption and translocation compared to fluazifop with once-refined or degummed seed oils.

Field research was conducted in Nebraska to evaluate the efficacy of herbicides for the control of summer annual weeds in sorghum [Sorghum bicolor (L.) Moench.]. During 1976 to 1979, no-till plots treated with a mixture of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], and terbutryn [N-(1,1-dimethylethyl)-N′-ethyl-6-(methylthio)-1,3,5-triazine-2,4-diamine] yielded 33% more sorghum grain than plots receiving the same herbicides when a seedbed was prepared by disking. During 1981 to 1983, season-long weed control was obtained with acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl) acetamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile}, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], or terbutryn added to paraquat plus atrazine and metolachlor plus cyanazine plus paraquat applied 10 days prior to planting. The use of seed safeners did not increase sorghum yield.

Red rice (Oryza sativa L. # ORYSA) control in soybeans [Glycine max (L.) Merr.] was 93% or more with shallow-incorporated alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] at 3.9 kg ai/ha, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 2.8 kg ai/ha, and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] at 1.7 kg ai/ha. Junglerice [Echinochloa colonum (L.) Link. # ECHCO] control was 80% with alachlor but 90% or more with metolachlor and trifluralin when applied at the same rates. Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} at 560, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy]phenoxy]propanoic acid} at 280, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} at 140, and mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} plus bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4 (3H)-one 2,2-dioxide] at 140 plus 840 g ai/ha applied postemergence on two- to four-leaf red rice provided at least 87% control. Junglerice control with these treatments was 85% or more with the exception of fluazifop and mefluidide plus bentazon.

CGA 82725 {2-propynyl [2-[4-[(3,5-dichloro-2-pyridinyl)oxy)] phenoxy] propanoate}, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy]phenoxy] propanoic acid}, sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, and fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} were applied postemergence to Texas panicum (Panicum texanum Buckl. # PANTE), large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA], and broadleaf signalgrass [Brachiaria platyphylla (Griseb.)Nash. # BRAPP] in peanut (Arachis hypogaea L. ‘Florunner’). Fluazifop applied at 280 and 410 g ai/ha, sethoxydim at 340 g ai/ha, haloxyfop at 140 g ai/ha, and CGA 82725 at 280 g ai/ha usually gave better control when applied to annual grasses in the two- to four-leaf stage than when applied at the six- to eight-leaf stage. Higher rates of application were required to provide acceptable weed control at the later stage of growth. Peanut yields were usually higher following the early applications, indicating that timing of application is important in obtaining improved yields.