Studies in growth chambers indicated that CGA-43089 {α-[(cyanomethoxy)imino] benzeneacetonitrile} applied at a rate of 1.25 g/kg of seed reduced the phytotoxicity of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], bensulide [o,o-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl) benzenesulfonamide], EPTC (S-ethyl dipropylthiocarbamate), UBI-S734 {2-[(1,2,5-dimethylphenyl)ethylsulfonyl] pyridine N-oxide} and MBR-18337 {N-[4-(ethylthio)-2-(trifluoromethyl)phenyl] methanesulfonamide} to grain sorghum [Sorghum bicolor (L.) Moench] during seed germination and seedling emergence. The protected sorghum tolerated metolachlor over a wider range of rates than it tolerated the other herbicides. CGA-43089 did not protect sorghum from the phytotoxicity of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine). Of seven other oximes tested as seed treatments, dimethylglyoxime, benzophenone oxime, pyridine-2-aldoxime, benzoin-α-oxime, and methyl thioacetohydroxamate showed promise for increasing the tolerance of grain sorghum to metolachlor. In general, higher rates of these oximes than the rate of CGA-43089 were required for equivalent protection of sorghum.

Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] uptake from solution by excised velvetleaf (Abutilon theophrasti Medic.) root segments was studied. Initial atrazine absorption by 1-cm segments cut from the apical 5 cm of roots was rapid. Atrazine concentration in the tissue became equal to the external atrazine concentration by 30 min. Atrazine did not accumulate in the root tissue to concentrations above the external solution, and rapid efflux of atrazine occurred when the root segments were washed with atrazine-free solution. Atrazine absorption was linear over a range of external atrazine concentrations. Dinitrophenol and KCN increased atrazine absorption during the first 3 min of exposure to atrazine. Anoxia increased atrazine absorption but decreased K+ uptake. Decreasing temperatures decreased atrazine absorption. Q10 values for atrazine uptake were between 1.3 and 1.4. The response of atrazine absorption by the excised roots to inhibitors, anoxia, external atrazine concentration, and temperature indicated simple diffusion as the mechanism of absorption of atrazine by velvetleaf roots.

Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 1 × 10−5 and 1 × 10−4 M increased the leakage of previously absorbed, 32P-labeled orthophosphate from the roots of onion (Allium cepa L.), a susceptible species, by 14 and 41 times the control values, respectively. A significant amount of 32P leaked from the roots of the moderately susceptible species, cotton (Gossypium hirsutum L. ‘DPL 61′) and cucumber (Cucumis sativus L. ‘Ashley′), whereas no significant loss of 32P occurred from two tolerant species, soybean [Glycine max (L.) Merr. ‘Bragg′] and corn (Zea mays L. ‘Pioneer 3369A′). At either 1 × 10−7 or 1 × 10−6 M, 1,8-naphthalic anhydride (NA) prevented 32P leakage from onion roots in the presence of 1 × 10−5 M metolachlor. High concentrations of NA [0.1% (w/v) suspensions], however, promoted 32P leakage and did not protect onion roots from the leakage induced by high concentrations (1 × 10−4 M) of metolachlor. Neither metolachlor nor alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], at 1 × 10−4 M, inhibited the uptake of acetate-2-14C or malonic acid-2-14C into excised cotton root tips or the incorporation of the precursors into lipids. Similarly, neither herbicide inhibited phospholipid synthesis by cotton root tips. Incorporation of 14C-choline chloride into phosphatidylcholine was not significantly inhibited by metolachlor.

Lath-house experiments were conducted to compare the effect of wild oat (Avena fatua L.) competition on two wheat (Triticum aestivum L. ‘Anza’ and T. turgidum durum group ‘Mexicali′) genotypes at three nitrate concentrations. Plants were grown to maturity in pots containing 10 wheat or wild oat plants, or mixtures of 10 wheat and 10, 25, or 50 wild oat plants. Nitrate was supplied in 500 ml Hoagland's solution with 1.5, 7.5, or 15.0 mM nitrate, as K and Ca nitrate, every 4 days. When grown without competition, Anza had more above-ground plant weight and grain yield and less whole-plant percent nitrogen than Mexicali. Wild oat competition caused larger reductions in plant weight and grain yield, and smaller reductions in percent nitrogen for Anza than for Mexicali. Wild oat competition reduced the effectiveness of nitrate in increasing plant weight, grain yield, and whole-plant percent nitrogen of wheat.

Intraspecific interference of populations of sunflower (Helianthus annuus L.) and velvetleaf (Abutilon theophrasti Medic), as well as interspecific populations of these two broadleaf weeds, in sugarbeets (Beta vulgaris L. ‘Mono Hy D2′) was determined in 2-yr field experiments. Sunflower was more competitive in sugarbeets than was velvetleaf. At densities of 6, 12, 18, and 24 sunflower plants/30 m of row, root yields were reduced 40, 52, 67, and 73%, respectively. At the same densities of velvetleaf, root yields were reduced only 14, 17, 25, and 30%, respectively. Interspecific interference of these two broadleaf weeds at the same densities reduced root yields 19, 36, 43, and 56%, respectively. The minimum number of weeds required/30 m of row to reduce sugarbeet root yields was predicted to be 1 for sunflower, 9 to 12 for velvetleaf, and 2 to 7 for an equal population of sunflower and velvetleaf.

The effects of chemical desiccation of bermudagrass [Cynodon dactylon (L.) Pers.] before seed harvest on seed yield and quality were studied. Harvest of 57.3% of available seed was obtained with the stripper harvester after chemical desiccation with paraquat (1,1′-dimethyl-4,4′-bipyridinium ion). Only 44.6% of the available seed was harvested by direct combining after paraquat treatment. This was significantly better than the 31.2% seed obtained by harvesting using the conventional swathing and combining method. Paraquat severely reduced germination of unhulled seeds. The inhibitory effects of paraquat application were removed by hulling or by hulling and scarifying the caryopses before germination. Significant improvement in germination of all seed (unhulled, hulled, and hulled-scarified) resulted from use of 0.2% KNO3 rather than water as a substrate moistening agent.

Dormant, dehulled red rice (Oryza sativa L. ‘Louisiana strawhulled′) germinated 80 to 90% at 30 C upon exposure to 10-3 M kinetin (6-furfurylaminopurine), benzyladenine (6-benzylaminopurine), or isopentenyladenine [6-(3-methylbut-2-enylamino)purine] at pH 3.5. Zeatin [6-(4-hydroxy-3-methylbut-trans-2-enylamino)purine] was also active, eliciting 45% germination at 10-3 M. Adenine was inactive at concentrations as high as 10-2 M. There was little influence of light and no effect of initial pH of the medium upon cytokinin-stimulated germination. At 20 C the response to cytokinins was reduced, but germination of non-dormant seeds was not prevented. At 30 C, the germination of dehulled red rice with 10-3 M kinetin occurred rapidly, with almost 70% germination after 2 days. When dehulled seeds were incubated in water and then transferred to kinetin, percent germination decreased as the duration of water incubation increased. The loss of cytokinin response did not parallel the timecourse of imbibition. Cytokinins did not break dormancy of intact seeds. The hull appeared to limit kinetin uptake and inhibited germination even when kinetin was forced into intact seeds by vacuum infiltration. Dry-after-ripening of intact seeds at 30 C did not increase the kinetin-sensitivity of intact red rice.

To simulate the effect of MSMA (monosodium methanearsonate) drift onto rice (Oryza sativa L. 'Starbonnet’ or ‘Labelle′), foliar applications at 0.20 to 0.78 kg/ha were made on rice at stages of maturity ranging from early tillering to panicle emergence. Foliage, sampled 1 to 2 weeks after application, and grain and grain parts harvested at maturity were analyzed by arsine generation atomic absorption spectrophotometry. Washed foliage contained 0.7 to 1.5 ppm background As, and 1 to 21 ppm As after MSMA application. The As content depended on application rate, stage of maturity at application, and the formulation of MSMA. Arsenic concentrations in grain increased exponentially as the time of application approached harvest, ranging from 0.25 to 7 ppm. There was little correlation between grain residues and rates, principally because dependence on the time of application was overriding. This study confirms previous observations that there is a specific stage in rice plant development, probably meiosis, during which rice is susceptible to sterilization by arsenic, and also indicates that significant yield reduction can occur from MSMA drift even when visual injury symptoms are not obvious.

Research involved the behavior of BAS-9052 OH {2[1-(ethoxyimino)butyl]-5-[2(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} in soybean [Glycine max (L.) Merr.] and johnsongrass [Sorghum halepense (L.) Pers.] plants, and the fate of 14C-BAS-9052 OH in intact plants and cell cultures of both species. Microscopic examination of seedling johnsongrass plants (two- to three-leaf stage) treated with foliar applications of 0.48 μg/plant revealed disorganized apical regions and necrotic cells within the apex and leaf primordia of the shoot. Necrotic zones were also evident at the base of expanding leaves and in root apices 1 day after treatment. Following application of 14C-BAS-9052 OH, the same radioactive products were isolated from cell cultures and intact plants. Products included BAS-9052 OH and three unidentified metabolites. Greater proportions of unchanged BAS-9052 OH were extracted from the apical leaves, roots, and cell cultures of johnsongrass than of soybean. BAS-9052 OH was thermal and photo-labile, and a large portion of 14C may not have entered the plant as BAS-9052 OH. However, tolerant soybean plants and cell cultures appeared to have metabolized the herbicide more rapidly than susceptible johnsongrass plants and cell cultures. An average of 64% of the 14C remained in the treated leaf of johnsongrass compared with 48% in soybean. About one-half as much 14C was translocated to the apical leaves of susceptible johnsongrass than tolerant soybean. Therefore, differential uptake and translocation cannot account for the selectivity of BAS-9052 OH.

In field tests, common cocklebur (Xanthium pensylvanicum Wallr.) was controlled at the one- and two-leaf stages with 0.3 kg/ha acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}. Four-leaf common cocklebur required 1.1 kg/ha for comparable control. Acifluorfen at 0.6 and 0.8 kg/ha controlled 96 and 90% of entireleaf morningglory [Ipomoea hederacea (L.) Jacq. var. integriuscula] atone- and two-leaf stages, respectively, but control was reduced as plants aged. Dark applications (2100 h) were more effective than those at sun-up (0600 h) or midday (1200 h) in control of hemp sesbania [Sesbania exaltata (Raf.) Cory], pitted morningglory (Ipomoea lacunosa L.), and smooth pigweed (Amaranthus hybridus L.). Hour of application had no significant influence on control of common cocklebur or prickly sida (Sida spinosa L.). An increase in surfactant (80% alkyl aryl polyoxyethylene glycols) concentration enhanced acifluorfen control of entireleaf morningglory and Texas gourd [Cucurbita texana (A.) Gray] at the 0.3-kg/ha rate applied 2 weeks after emergence. Soybean [Glycine max (L.) Merr.] injury was increased with the 1.1-kg/ha rate when surfactant concentration was increased from 0.5 to 0.75%. Increasing the spray volume increased pitted morningglory control but decreased hemp sesbania control. In the growth chamber, better control of pitted morningglory and common cocklebur was obtained at high (35 C day, 26 C night) than at low temperatures (27 C day, 18 C night) when plants were treated 1 week after emergence.

Quadratic response surface analysis was applied to data of seed germination in relation to temperature. Analysis of these data is the comparing of several levels of quantitative factors. In such situations, multiple-comparison procedures, such as Duncan's multiple range test, are inappropriate. The data were the germination percentages of four species at 55 constant or alternating day and night temperature regimes. A quadratic response surface was developed for each species using multiple-regression techniques. Estimated germination values and their confidence limits were derived from the quadratic response surface of each species for each cold-period temperature through a series of warm-period temperatures. Many parameters were synthesized from the response surfaces to evaluate germination of the four species in relation to temperature. These comparisons form a statistically valid basis from which to select the most adapted plant species and predict the best time for planting or applying weed-control treatments.

A method is described to produce inoculum of Alternaria cassiae Jurair and Khan for biocontrol studies. Approximately 8 g of a conidial preparation containing 1 × 108 conidia/g were produced per liter of growth medium. In greenhouse studies the effectiveness of A. cassiae as a biocontrol agent for sicklepod (Cassia obtusifolia L.) was affected by dew-period temperature, dew-period duration, inoculum concentration, and the stage of growth of sicklepod seedlings at the time of inoculation. Optimum environmental conditions included at least 8 h of free moisture at 20 to 30C. Spray mixtures containing approximately 5 × 104 or more conidia/ml gave maximum control when sicklepod seedlings were sprayed to runoff. Sicklepod seedlings in the cotyledon to first-leaf stage were most susceptible to the pathogen.

Caffeic acid, chlorogenic acid, coumarin, p-coumaric acid, ferulic acid, fumaric acid, gallic acid, hydrocinnamic acid, p-hydroxybenzoic acid, juglone, and pyrocatechol were examined for effects on germination of nine crop and weed species: cotton (Gossypium hirsutum L.), cantaloupe (Cucumis melo L.), corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], hemp sesbania [Sesbania exaltata (Raf.) Cary], sicklepod (Cassia obtusifolia L.), velvetleaf (Abutilon theophrasti Medic), prickly sida (Sida spinosa L.), and redroot pigweed (Amaranthus retroflexus L.). Germination tests with 10-3 and 10-5 M solutions were conducted under controlled conditions in petri dishes at 25 C in the dark. At 10-3 M, coumarin, hydrocinnamic acid, juglone and pyrocatechol inhibited germination, but p-hydroxybenzaldehyde and p-hydroxybenzoic acid were not effective and others had intermediate effects. There was little effect by any compound at 10-5 M. Chlorogenic acid, p-hydroxybenzaldehyde, and pyrocatechol, each combined with coumarin, inhibited germination. The combination of coumarin plus p-hydroxybenzaldehyde had an additive effect on hemp sesbania and prickly sida, inhibiting germination to a greater extent than either compound alone. The lack of inhibitory action at the higher concentration of some of these chemicals suggests they may not exhibit a high allelopathic potential.

Greenhouse and field experiments were conducted with a roller applicator at Lincoln, Nebraska, during 1979 and 1980. Glyphosate [N-(phosphonomethyl)glycine] concentrations of 5, 10, and 20% and carpet saturations of 50 and 75% controlled shattercane [Sorghum bicolor (L.) Moench] when applied to the top 30 cm of the plant in greenhouse research. In the field, glyphosate concentrations of 5 to 20% with a carpet saturation of 50% controlled shattercane acceptably in soybeans [Glycine max (L.) Merr.], but a concentration of 2.5% with 25% carpet saturation did not. Weed control was comparable whether speed of application was 3.2, 6.4, or 9.6 km/h. Shattercane control in grain sorghum [Sorghum bicolor (L.) Moench.] was excellent at glyphosate concentrations of 5, 10, and 20% and at carpet saturations of 50 and 75%, and sorghum injury was minimal at 25 and 50% carpet saturations. The roller applicator was compared to a ropewick applicator for shattercane control in sorghum. Excellent weed control (90% or greater) with minimal crop injury was obtained with the roller applicator at glyphosate concentrations of 10 and 20% at application speeds of 3.2 and 6.4 km/h and with the ropewick applicator with glyphosate concentrations of 35 and 50% applied at 3.2, 6.4, and 9.6 km/h.

Diffuse knapweed (Centaurea diffusa Lam.) and spotted knapweed (C. maculosa Lam.) presently infest approximately 1.5 million ha of pasture and rangeland in Washington, Montana, Idaho, Oregon, and California. The serious losses caused on lands where returns from herbicidal control are marginal or less prompted the testing and introduction of two strains of a seed-head fly (Urophora affinis Frlfld.) as a biological-control agent in these states. Over 27 000 flies were released in about equal numbers on both weeds during the years 1974 to 1977 and in 1979 and 1980. The fly became established in all states where it was released. The adult was found to disperse over 76 m from release point from 1974 to 1976, and to reduce the number of seeds per flower head in sampled heads by 80% in northern Washington and over 64% at the Heppner, Oregon site. A newly released moth (Metzneria paucipunctella Zell.) and a root-boring beetle (Spbenoptera jugoslavica Obenb.) are expected to cause additional pressure on these plants. The reproductive potential of the knapweeds is such that more natural enemies will be needed to provide enough stress to reduce these weedy species to an acceptable level.

The comparative susceptibility of weedy okra [Abelmoschus esculentus (L.) Moench.] and three commercial okra cultivars (′Dwarf Green Long Pod′, ‘Clemson Spineless', and ‘White Velvet′) to six preemergence herbicides was evaluated in the greenhouse. Okra can be controlled in cotton (Gossypium hirsutum L.) and soybean [Glycine max (L.) Merr.] fields with appropriate preemergence herbicide use. Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one] completely controlled okra at 0.2 to 0.8 kg/ha. Fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] at 0.9 to 1.8 kg/ha and cyanazine {2-[[4-chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile} at 1.2 to 2.4 kg/ha controlled okra, but at the 0.6 kg/ha rate cyanazine did not control wild okra and fluometuron at 0.45 kg/ha did not completely control any cultivar. Norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3 (2H)-pyridazinone] bleached the cotyledons and young leaves of okra, but gave 50% or less control even at 2.4 kg/ha. Both the weedy and commercial okras were completely resistant to trifluralin (α,α,α-trifluoro-2,6-dinitro -N,N-dipropyl-p-toluidine) and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] but higher rates of these herbicides affected okra growth.

Aerial applications of pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} at 0.5 kg/ha reduced creosotebush [Larrea tridentata (DC.) Coville] density by up to 86% and by 99% when applied at 1 kg/ha in February or March. Grass production 32 months after treatment was 174 to 305% greater in tebuthiuron-treated plots than on untreated ran gel and, but forb production in treated plots was reduced 38% or more and the poisonous half-shrub broom snakeweed [Gutierrezia sarothrae (Pursh) Britt. and Rusby] was reduced 94% or more.

Laboratory and field studies were conducted to examine the influence of R-33865 (O, O-diethyl-O-phenol phosphorothioate) on the degradation rate of EPTC (S-ethyl dipropylthiocarbamate) in three soils that had a history of repeated EPTC application and exhibited accelerated degradation of EPTC. In field studies, addition of R-33865 to EPTC extended EPTC persistence in soil and provided increased shattercane [Sorghum bicolor (L.) Moench] control. In two soils that exhibited rapid EPTC degradation, addition of R-33865 to EPTC extended the half-life of EPTC from 9 to 18 days and from 6 to 15 days, respectively. Evolution of 14CO2 from 14C-carbonyl EPTC-treated soils with a prior history of EPTC treatment was significantly reduced when R-33865 was added; however, the initial lag period of EPTC degradation was not restored. Addition of R-33865 to EPTC on soils with no prior EPTC treatment did not extend persistence of EPTC in soil.

The relationship between pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone] in soil solution and dosage was examined in two soils under slurry equilibrium conditions and at field water capacity. In a sandy soil, the partition coefficient, calculated from a regression analysis of soil water content on dosage applied, was similar under slurry conditions and at field water capacity, but in a loamy sand, high in organic matter, the partition coefficient was somewhat higher at field water capacity than the estimated 4.71 measured in a great excess of water. In the sandy soil, neither the partition coefficients under slurry conditions nor at field water capacity were significantly different from Freundlich's k. Under slurry conditions in the loamy sand this difference was barely significant, whereas at field water capacity the estimated partition coefficient was significantly higher than Freundlich's k. Soil water sampling at field water capacity a fortnight after the start of the experiment showed a considerable increase in partition coefficient compared with the first sampling after 2 days, and the relationship in a sandy soil showed a slight non-linear trend, but that of the loamy sand still appeared to be linear. A desorption experiment indicated that the recovery of soil-adsorbed pyrazon was almost complete.

Tubers of yellow nutsedge (Cyperus esculentus L.) were collected over a 2-yr period to investigate the variation in abscisic acid (ABA) and total phenols throughout the year. The amount of ABA increased gradually from the end of the summer to November when it reached the highest level (6.81 μg/g fresh wt of tubers). This coincided with the onset of dormancy of the tubers in the field. In April, when a maximum of tubers showed sprouting, no free ABA was detected in tuber extracts. These data seem to indicate that free ABA is, in part at least, responsible for the dormant state of tubers. No obvious relation was seen between the state of dormancy of the tubers and their total phenolic content. It is unlikely that the phenolics as a group have one specific role in regulating dormancy of the tubers, but is possible that individual classes, or individual phenols, may possess significant activity.