Response of wild oat (Avena fatua L.) at the three-leaf stage to five postemergence herbicides, asulam (methyl sulfanilylcarbamate), barban (4-chloro-2-butynyl m-chlorocarbanilate), diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, difenzoquat (1,2-dimethyl-3,5-diphenyl-1 H-pyrazolium), and flamprop [N-benzoyl-N-(3-chloro-4-fluorophenyl)-DL-alanine] was measured and compared in nine physiological and biochemical processes (chlorophyll content, photosynthesis, photosynthate translocation, and changes in ATP, lipids, DNA, RNA, amino acids, and proteins). Content of chlorophyll a and b was reduced by the application of diclofop and difenzoquat. Photosynthesis was inhibited with all five herbicides, but photosynthate translocation from the leaves to the roots was reduced only with diclofop, difenzoquat, and flamprop. ATP production was inhibited by all herbicides except flamprop, which increased the ATP content. Incorporation of 32P into lipids was reduced by all herbicides except asulam. The incorporation of 32P into nucleic acids (DNA and RNA) was inhibited by all five herbicides. Serine and threonine, especially the latter, accumulated in large quantity with all herbicides except difenzoquat. Protein content (water-soluble,-insoluble, and total amount) was reduced by asulam, diclofop, and flamprop, but barban and difenzoquat reduced water-insoluble and total proteins only. Apparently, all herbicides examined affected more than one physiological function and biochemical process in wild oat.

GAF 141 [(2-chloroethyl)phosphonic acid plus N-methylpyrrolidone] increased basipetal translocation of glyphosate [N-(phosphonomethyl)glycine], dicamba (3,6-dichloro-o-anisic acid), and acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxyl]-2-nitrobenzoic acid} in bean seedlings (Phaseolus vulgaris L. 'Stringless Greenpod′). The GAF 141 was applied as a foliar treatment before or at the same time as herbicide injection into the cotyledonary node. GAF 141 applied 24 h prior to glyphosate, dicamba, or acifluorfen injection enhanced basipetal translocation to the roots and inhibited acropetal translocation to the young shoots. GAF 141 applied simultaneously with the herbicide injection did not have substantial effects on translocation. Greater basipetal translocation of acifluorfen occurred at high (75 ± 5%) than at low relative humidity (35 ± 5%).

Three cultivars of wild rice (Zizania palustris L.) were grown with various densities of common waterplantain (Alisma triviale Pursh) established from seeds and from rootstocks during 1979 and 1980. Wild rice cultivars did not differ in their response to common waterplantain interference. Common waterplantain grown from seeds at densities up to 82/m2 did not significantly reduce wild rice yield. Common waterplantain established from rootstocks significantly reduced wild rice yield at densities as low as 3/m2. A density of 43/m2 reduced wild rice yield by 91%. The yield component most susceptible to interference from common waterplantain was panicles per plant. The number of seeds per panicle was reduced by densities as low as 11/m2 and seed weight was reduced by densities of 22/m2 or greater. Only a density of 43/m2 reduced the stand of wild rice. Common waterplantain established from rootstocks at a density of 17 plants/m2 did not reduce wild rice yield if removed by 7 weeks after planting. Interference from common waterplantain for 9 weeks or longer reduced wild rice yield by approximately 50%.

Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl) acetanilide], acetochlor [2-chloro-N-(ethoxymethyl)-6′-ethyl-o-acetotoluidide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] were adsorbed in similar amounts, approximately one-third that of the reference compound prometryn [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] by Ca-organic matter and seven soils. Adsorption isotherms for the four herbicides by Ca-montmorillonite were of the same shape, but different bonding mechanisms were involved. Adsorption and bioactivity of the acetanilide herbicides were correlated with organic matter, clay content, and other soil parameters as determined by two different soil- testing laboratories.

Alfalfa (Medicago sativa L. ‘Vernal′) seeded in April in rows 55 cm apart and kept free of weeds produced 820 kg/ha of seed during the year of seeding. Competition from a dense popualtion (40 plants/m of row) of mixed species of annual weeds reduced the seed yield to 45 kg/ha. Competition from a dense population (55 plants/m of row) of broadleaf weeds, a light population (4 plants/m of row) of broadleaf weeds, or a heavy population (75 culms/m of row) of barnyardgrass [Echinochloa crusgalli (L.) Beauv.] reduced yields to 80, 310, and 160 kg/ha, respectively. A weed management system, consisting of EPTC (S-ethyl dipropylthiocarbamate) or profluralin [N-(cyclopropylmethyl)-α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine] applied at or before planting, 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid] applied postemergence, trifluralin (α,α,α- trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) incorporated with the soil when the alfalfa was 20 cm tall, interrow tillage, and a modest input of hand labor brought the crop to harvest free of weeds, and the yields of alfalfa seed were similar to those from plots kept weed-free by hand labor only. When weeds within the rows were controlled by hand labor only, labor inputs as great as 930 h/ha were required to bring the crop to harvest free of weeds, whereas labor inputs of 7 to 17 h/ha removed all surviving weeds when effective weed management systems had been applied.

The effects of shade on dry-matter production, leaf area, and biomass partitioning in purple nutsedge (Cyperus rotundus L.) and yellow nutsedge (C. esculentus L.) were determined in a controlled-environment greenhouse with a day/night temperature regime of 32/26 C. For comparison with a full-light treatment, screening provided 40, 70, and 85% shade. Shading significantly reduced height of yellow nutsedge and dry-matter production, leaf-area production, and rhizome and tuber formation of both species. Shading decreased the partitioning of plant biomass into tubers and rhizomes and increased partitioning into leaves. Yellow nutsedge had a higher net-assimilation rate than purple nutsedge at all levels of shading, but the greater leaf-area duration or total amount of leaf area present in purple nutsedge resulted in greater dry-matter production by that species. The responses of the two species showed no differences in shade tolerance.

The absorption, translocation, metabolism, and retention of an isopropylamine formulation of glyphosate [N-(phosphonomethyl)glycine] in the presence and absence of the commercial dimethylamine salt and isooctyl ester formulations of 2,4-D [(2,4-dichlorophenoxy)acetic acid], or the commercial isooctyl ester formulation of bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) was investigated in barley (Hordeum vulgare L. 'Summit′). In all treatments, absorption of 14C-glyphosate continued for up to 24 h, but no further absorption occurred with a further 48 h of treatment. A considerable reduction in absorption and translocation of 14C-glyphosate occurred when it was applied to the leaf surface in a mixture with the commercial formulation of either 2,4-D amine, 2,4-D ester, or bromoxynil. When a 14C-glyphosate solution was spotted on the leaf adjacent to drops of the commercial formulation of either 2,4-D amine, 2,4-D ester, or bromoxynil, no reduction in absorption or translocation of 14C-glyphosate occurred. The herbicide components of the 2,4-D amine and bromoxynil formulations were solely responsible for reduced absorption and translocation of 14C-glyphosate. No 14C-glyphosate metabolites were detected in barley following treatment with 14C-glyphosate either alone or mixed with the commercial formulations of 2,4-D amine or bromoxynil. No 14C-glyphosate complexes were detected in mixtures of the commercial formulations of 2,4-D amine, 2,4-D ester, or bromoxynil with 14C-glyphosate. Barley leaves retained less glyphosate when it was spray-applied together with the commercial formulation or the solvent system of 2,4-D amine.

A method is presented to determine which of a set of sampling techniques is most nearly optimum for sampling weed abundance. To employ the method, one needs first to develop a set of sampling alternatives. A pilot survey is then conducted to determine time costs and sampling and measurement error variances associated with each technique. We used this method to determine which of three plot sizes (0.6 by 0.6 m, 0.6 by 1.5 m, 1.2 by 2.1 m) and two types of orchard scans is most nearly optimum for estimating weed abundance in apple [Malus domestica (Bork)] orchards. The results indicate that, for weed species that are fairly apparent, orchard scans are optimal when less than 8 h of sampling effort is expended, but when a high degree of precision is required, or when the weed species is more difficult to detect, plot samples may be the better choice. A size of plot ca. 0.6 by 1.5 m size was found to be most nearly optimum.

Field studies were conducted in 1978 and 1979 on broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash] management in peanuts [Arachis hypogaea (L.) ‘Florigiant′]. In both years, preplant incorporated applications of benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] provided better than 75% initial control of broadleaf signalgrass. Preemergence applications of alachlor and metolachlor provided 90% or better initial control. Vernolate (S-propyl dipropylthiocarbamate) and diphenamid (N,N-dimethyl-2,2-diphenylacetamide) provided less than 45% initial control. An at-cracking application of dinoseb (2-sec-butyl-4,6-dinitrophenol) plus naptalam (N-1-naphthylphthalamic acid) plus either alachlor or metolachlor increased control over that provided by at-planting herbicides alone and maximum yields were obtained. No at-planting herbicide alone provided better than 60% control at harvest and consequently yields were lower. In three of four experiments, sequential applications of at-planting and at-cracking herbicides provided better than 75% control at harvest. In the fourth experiment, only benefin and metolachlor followed by at-cracking applications provided better than 70% control at harvest.

Interference studies utilizing natural infestations of broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash] in peanuts [Arachis hypogaea (L.) ‘Florigiant′] were conducted at two sites in 1978 and repeated at the same sites in 1979. Full-season interference from broadleaf signalgrass populations of 8, 16, and 1050 plants/10 m of row reduced seed yields 14, 28, and 69%, respectively. Linear regression analysis showed that slightly less than 4 plants/10 m of row significantly reduced yields. Broadleaf signalgrass interference with peanuts for 6 weeks or less after planting did not reduce seed yields; however, interference for 8 weeks or longer after planting did. Peanuts kept weed-free for 6 weeks or more after planting had seed yields equal to peanuts kept weed-free all season. Full-season broadleaf signalgrass interference reduced mature peanut forage yields 64%, but peanut interference only reduced broadleaf signalgrass forage yield 10%.

Benazolin (4-chloro-2-oxobenzothiazolin-3-ylacetic acid) formulated as the dimethylamine salt was evaluated for common cocklebur (Xanthium pensylvanicum Wallr.) and prickly sida (Sida spinosa L.) control in soybeans [Glycine max (L.) Merr.] between 1977 and 1979. Benazolin was applied alone or in admixtures with acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid}, bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4 (3H)-one 2,2-dioxide], dinoseb (2-sec-butyl-4,6-dinitrophenol) plus naptalam (N-1-naphthylphthalamic acid), and 2,4-DB [4-(2,4-dichlorophenoxy)butyric acid] over-the-top of soybeans {V3 to V12 [V(N); vegetative stage with “N” nodes on the main stem beginning with the unifoliolate node]}. Benazolin effectively controlled common cocklebur at rates of 0.2 and 0.4 kg/ha. Soybean tolerance was acceptable even with a repeat application of 0.4 kg/ha. Early-season (July) control was less than late season (August) because it took 2 to 3 weeks for benazolin to kill common cocklebur. Prickly sida control was poor with benazolin even at 0.6 kg/ha. Soybean tolerance and seed yields were higher when soybeans were treated with admixtures of benazolin plus bentazon than with benazolin alone. Antagonism was observed with this admixture for prickly sida and late-season common cocklebur control. Antagonism was eliminated with ratios of benazolin to bentazon of 1 to 3 applied in a single application or a 1 to 1.5 ratio repeated.

Of 15 pesticides evaluated in a screening test with respect to their effects on growth and nitrogen assimilation of the Azolla mexicana (Presl) – Anabaena azollae (Strasburger) symbiosis, the bipyridilium and phenolic herbicides at 0.1 ppmw were the most detrimental, causing up to a 75% reduction in nitrogen fixation and nitrate reduction with little or no effect on growth. Chloramben [3-amino-2,5-dichlorobenzoic acid] at 1.0 ppmw, and dicamba [3,6-dichloro-o-anisic acid], and benomyl [methyl-1-(butylcarbamoyl)-2-benzimidazolyl carbamate] at 10.0 ppmw caused an 84 to 99% reduction in nitrogen fixation without affecting nitrate reduction or growth. Simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] at 10.0 ppmw stimulated nitrate reduction 20 fold, causing a 99% reduction in nitrogen fixation. Growth and nitrogen assimilation were reduced at similar concentrations between 0.1 and 10 ppmw for each of the other benzoic, triazine, dinitroanaline, and urea herbicides tested. Naptalam [N-1-naphthylphthalamic acid] was the only pesticide tested that had no effect on growth or nitrogen assimilation at 10.0 ppmw.

Experiments were conducted to determine the influence of the dimethylamine salt of MCPA {[(4-chloro-o-tolyl)oxy] acetic acid} pretreatment, darkness from 1 day prior to treatment until harvest, and exogenous sucrose on diclofop {2-[4-(2,4-dichlorophenoxy)phenoxyl] propanoic acid} glucose, and sucrose uptake and translocation by wild oat (Avena fatua L.). Uptake of 14C-diclofop label by wild oat foliage was not influenced by MCPA pretreatment, constant dark treatment, or the addition of exogenous sucrose. Total 14C-diclofop and 14C-glucose label uptake and translocation were similar whether 5 cm of the treated leaf tip were placed in distilled water or 1% (w/v) sucrose. Downward translocation of 14C-diclofop, 14C-sucrose, and 14C-glucose label in the phloem of wild oat was reduced similarly by MCPA, constant dark treatments, or a combination of the two. Upward translocation of 14C-diclofop label was greater and exudation of 14C-diclofop label into the ‘tip’ solution was less than that of 14C-sucrose or 14C-glucose label, regardless of MCPA or constant dark treatments. Downward translocation of 14C-diclofop label was reduced as much by MCPA topically applied to the wild oat leaf 1 cm above, 1 cm below, or with the diclofop as with the MCPA broadcast pretreatment.

Field experiments were conducted to determine the effectiveness of the herbicide antidote R-25788 (N,N-diallyl-2,2-dichloroacetamide) in protecting corn (Zea mays L.) cultivars from EPTC (S-ethyl dipropylthiocarbamate) injury. Preplant-incorporated applications of EPTC, with and without R-25788, were made to a fine sandy loam in 1976 and a loamy sand soil in 1977. EPTC at 6.7 kg/ha was 20 to 30% more injurious to the susceptible cultivars grown in sandy, lower organic-matter soil than in fine sandy loam. R-25788 did not decrease the weed-control efficacy of EPTC. The cultivar ‘TXS114’ was highly tolerant to EPTC at 6.7 kg/ha with or without antidote protection. Most of the other EPTC-susceptible cultivars showed significant stand improvement when R-25788 was used in combination with EPTC. R-25788 did not alleviate EPTC phytotoxicity toward ‘XL55’ and ‘XL379’ cultivars. EPTC applied in combination with R-25788 showed no, or only, slight injury to all other cultivars.

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.

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.

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.

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.

Ethylene-stimulated germination of witchweed [Striga lutea Lour. = S. asiatica (L.) O. Ktze.] seed first occurred after 13, 10, 6, 3, and 2 days of conditioning in moist sand at day/night temperatures of 20/14, 23/17, 26/20, 29/23, and 32/26 C, respectively. Maximum germination percentages in these regimes were 0.5, 3, 20, 24, and 37%, respectively. No germination occurred at 17/11 C. Witchweed seed survived in sand frozen for 7 weeks at −7 or −15 C and subsequently germinated in response to ethylene or in the presence of corn (Zea mays L., ‘DeKalb B73 × Mo.17H′) roots. The parasites emerged from the soil and flowered when maintained at 29/23 C after the termination of the freezing treatments. In other experiments, witchweed parasitized corn and/or sorghum [Sorghum bicolor (L.) Moench ‘DeKalb E-59+′] root systems in a sandy loam under 26/17, 26/20, 29/20, 32/23, and 32/26 C day/night regimes. Witchweed emerged from the soil with 26/20, 29/20, 32/23, and 32/26 C and flowered with 26/20, 32/23, and 32/26 C day/night regimes. Underground development and subsequent emergence of the parasites were substantially reduced with day/night temperatures below 29/20 C. Winter soil temperatures and growing season soil and air temperatures are unlikely to limit the spread of witchweed into important corn- and sorghum-producing areas of the United States.

Of 15 hard red winter wheat (Triticum aestivum L.) cultivars grown on several soil types and treated in the spring with several rates of metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazine-5(4H)-one], ‘Lindon’ and ‘Vona’ were the most sensitive and ‘TAM W 101’ and ‘Osage’ the most tolerant. Differences in cultivar response to metribuzin occurred in 9 of 13 locations, but were not observed when precipitation was very light or when the soil was saturated at the time of treatment. TAM W 101 was also more tolerant than Vona in the greenhouse.