Growth and the chlorophyll and carotenoid contents were measured in greenhouse-grown yellow nutsedge (Cyperus esculentus L. ♯ CYPES), following treatment with glyphosate [N-(phosphonomethyl)glycine]. Herbicide was applied as a foliar spray at concentrations of 0.1, 1.0, 5.0, and 10.0 mM. After 2 weeks, growth was inhibited, and chlorosis and leaf apex necrosis were observed. Plant height was reduced, leaf fresh weight was decreased by 40%, and leaf dry weight was slightly affected. Rhizome, tuber, and secondary shoot formation was strongly inhibited, but root development was not affected by glyphosate treatment. With the 10-mM treatment, dry weight of the underground system was reduced by 80%. Chlorophyll and carotenoid levels were decreased by 52 and 54%, respectively, following glyphosate treatment.

The effects of several inorganic salts on the toxicity and translocation of nonradiolabeled and 14C-radiolabeled MSMA (monosodium salt of MAA) and the isopropylamine salt of glyphosate [N-(phosphonomethyl)glycine] following foliar applications to purple nutsedge (Cyperus rotundus L. ♯ CYPRO) were evaluated. Salts of the monovalent cations NH4+, K+, and Na+ and to a lesser degree the anion PO4 generally resulted in increased toxicity of these herbicides. Salts of the divalent and trivalent cations Zn++ and Fe+++ frequently reduced the activity of glyphosate and MSMA, whereas salts of the divalent Ca++ ion caused little or no effect on activity. Salts of the anions Cl–, NO3–, CO3—-, and SO4– resulted in increased, decreased, or unchanged glyphosate toxicity as influenced by the associated cation. Translocation of the radiolabel of 14C-glyphosate and 14C-MSMA was increased by the addition of NH4Cl, while retention of the radiolabel within the tissue of the treated area was increased by the addition of FeCl3 to the treated leaf surface.

Investigations were made under controlled environmental conditions of isoproturon [N-(4-isopropylphenyl)-N’,N′-dimethylurea] absorption and translocation in wheat (Triticum aestivum L.) (tolerant) and slender foxtail (Alopecurus myosuroides Huds. ♯ ALOMY) (sensitive). Effects of isoproturon on 14CO2 fixation and 14C-assimilate translocation were also examined in the test species. The amount of 14C-isoproturon translocated by slender foxtail was about four times greater than by wheat. Foliar application of isoproturon resulted in greater inhibition of photosynthetic 14CO2 fixation in slender foxtail than in wheat. The reduction in 14C-assimilate translocation was also significantly greater in slender foxtail than in wheat.

Protein damage, as a primary phytotoxic consequence of in vivo lipid peroxidation, induced by the diphenyl ether herbicide oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene] at a concentration of 10 μM, was measured with the green alga Scenedesmus acutus. In the light, water-soluble proteins are destroyed by a herbicide-induced peroxidation process that can be detected by production of fluorescent products and loss of specific amino acid residues of proteins. The water-soluble cytochrome c-553 and the membrane-bound cytochrome f-553, components of the photosynthetic electron transport, were specifically used as sensitive markers for protein damage, measured as decrease of redox reactions of the cytochromes. Under peroxidizing conditions, destruction of the algal cytochrome c is significantly higher than destruction of membrane-bound components, such as cytochrome f and chlorophyll. Protection against protein loss is achieved by the nonbiological antioxidant ethoxyquin (1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline) or the photosynthesis inhibitor diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea].

14C-Sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} was rapidly metabolized by quackgrass [Agropyron repens (L.) Beauv. ♯ AGRRE], barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯ ECHCG], alfalfa (Medicago sativa L. ‘Saranac’), and navy bean (Phaseolus vulgaris L. ‘Seafarer’). One hour after application, 46, 27, 38, and 46% of the total 14C in the ethyl acetate-soluble fraction from treated leaves was sethoxydim, respectively. After 24 h, less than 2% was sethoxydim in any species. Nine metabolites were found, seven of which cochromatographed with photo- and thermal-transformation products of sethoxydim. Two metabolites, previously shown to be phytotoxic to barnyardgrass, contained the majority of 14C up to 24 h after application. Quantitative or qualitative differences in the metabolites of treated leaves could not account for the observed differences in selectivity.

Certain oximes, including cyometrinil [(Z)-α-(cyanomethoxy)iminobenzeneacetonitrile], CGA-92194 [N-(1,3-dioxolan-2-yl-methoxy)-iminobenzeneacetonitrile], 2-pyridinealdoxime-O-benzyl ether (PA-B), and 2-pyridinealdoxime-O-phenethyl ether (PA-PE), which are known to protect sorghum from chloroacetanilide herbicides, increased the toxicity of the insecticide propoxur (o-isopropoxyphenyl-methyl carbamate) to a resistant strain of housefly (Musca domestica L.). Flurazole [5-thiazolecarboxylic acid, benzyl ester, 2-chloro-4-(trifluoromethyl)], a nonoxime protectant for grain sorghum, had less effect on the toxicity of propoxur than did the oximes. Metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], which can be used as a herbicide in sorghum [Sorghum bicolor (L.) Moench.] only if the seed have been treated with a protectant, also increased the toxicity of propoxur to houseflies. Commercially available insecticide synergists increase insecticide activity by inhibiting NADPH-dependent microsomal mixed-function oxidase activity. Sorghum coleoptiles possessed the enzyme system necessary to oxidize aldrin (1,2,3,4,10,10-hexachloro-1,4,4a,5,8,8a-hexahydro-1,4-endo-exo-5,8-dimethanonaphthalene) to dieldrin (1,2,3,4,10,10-hexachloro-6, 7-epoxy-1,4,4a,5,6,7,8,8a-octahydro-1,4-endo-exo-5,8-dimethanonaphthalene), which is a standard test for oxidative metabolism in insects. Under the conditions of these tests, the aldrin epoxidase activity in sorghum coleoptiles was not affected by pretreatment with cyometrinil or flurazole.

In laboratory experiments, the effects of the herbicides HOE-39866 [ammonium (3-amino-3-carboxypropyl)-methylphosphinate] and SC-0224 (trimethylsulfonium carboxymethylaminomethylphosphonate) on the incorporation of NaH14CO3, [14C]-leucine, [14C]-uracil, and [14C]-acetate into enzymatically isolated soybean [Glycine max (L.) Merr. ‘Essex’] cells were evaluated to assess the activity of these herbicides on CO2 fixation, protein, ribonucleic acid (RNA), and lipid syntheses. At low concentrations neither compound exhibited rapid or distinct inhibitions of any process as might be expected in the case of inhibition of a primary target site. Photosynthesis was the process least affected. At equimolar concentrations, protein and RNA syntheses were more sensitive to HOE-39866 than to SC-0224 while the reverse occurred in lipid synthesis. Protein synthesis appears to be a possible target site that may be involved in the herbicidal action of these two compounds.

The effect of FMC 57020 [2-(2-chlorophenyl) methyl-4,4-dimethyl-3-isoxalidinone] on chloroplast development was examined in the cotyledons of 5-day-old, etiolated pitted morningglory (Ipomoea lacunosa L. ♯ IPOLA) seedlings grown from seeds inbibed for 24 h in water or 0.5 mM FMC 57020. In etiolated tissues, protochlorophyllide content was unaffected by FMC 57020; however, the herbicide eliminated carotenoid accumulation. There was no effect of FMC 57020 on phytoene or phytofluene content, although norflurazon [4-chloro-5-(methylamino)-2-(3-trifluoromethyl) phenyl)-3(2H)-pyridazinone] increased phytoene content in these tissues. The Shibata shift was greatly retarded in FMC 57020-treated cotyledons, suggesting that phytol levels are also reduced by the herbicide. There were no ultrastructural effects on etioplasts; however, under low white light (150 μE·m-2·s-1 PAR), plastids of FMC 57020-treated seedlings did not develop into chloroplasts but rapidly developed ultrastructural symptoms of photobleaching. Starch was not mobilized in herbicide-treated plastids and sugar levels were higher in these plastids than in control plastids. Etiolated hypocotyl growth was inhibited by FMC 57020, whereas norflurazon had no effect upon it. Our results suggest that FMC 57020 blocks both diterpene and tetraterpene synthesis.

Wild and cultivated proso millet (Panicum miliaceum L. ♯ PANMI) showed increased height and dry mass with increasing photoperiod and flowered under all photoperiods. Increasing planting density decreased height and dry mass and slowed seedhead development in both types. Shading increased plant height and decreased dry mass of both millets and increased germination compared to unshaded treatments. Planting date did not affect germination of freshly collected seed of either millet. Wild proso millet seed had a low germination rate until 8 weeks after panicle emergence, and the rate increased to 22% after 10 weeks. Germination of cultivated proso millet seed was low for 5 weeks after panicle emergence and increased to 92% after 10 weeks.

Research was conducted from 1979 through 1982 in east-central Alabama to monitor changes in sicklepod (Cassia obtusifolia L. ♯ CASOB) seed numbers in the soil under various cropping and weed management systems in soybeans [Glycine max (L.) Merr.]. Significant declines in sicklepod seed numbers were attained only when mechanical summer fallow each year prevented replenishment of seed in soil. Repeated disking favored germination and emergence of sicklepod seed and thus caused a reduction in seed numbers. Chemical summer fallow, which relied on postemergence control of emerged sicklepod, did not result in a disturbed seedbed and was less effective in reducing seed numbers. Permitting subcompetitive densities of sicklepod, 0.45 and 0.90 plants/m2, to reach maturity each year resulted in increases in seed numbers in the soil. Increases were more dramatic in conventionally planted soybeans than in no-till culture. Sicklepod produced more pods per plant in tilled culture than in no-till. Sicklepod seed distribution in the upper 30 cm of the soil was not affected by the type of primary tillage.

An annual weed, found in Minnesota in the summer of 1984, was identified as Polygonum bungeanum Turcz. This species is not included in floras of North America and may have been introduced from Asia as long ago as 25 yr. Because the stems of this weed are prickly, we propose “prickly smartweed” as a common name for this species. Currently, we know the weed to occur in six counties in southern Minnesota and one county in northern Iowa. Field observations suggest that this species may be at least as competitive as other annual smartweeds.

Cotton (Gossypium hirsutum L. ‘Stoneville 213’) was grown on Lucedale fine sandy loam with sicklepod (Cassia obtusifolia L. ♯ CASOB) and a complex of redroot pigweed (Amaranthus retroflexus L. ♯ AMARE) and smooth pigweed (A. hybridus L. ♯ AMACH) in all possible combinations of 0, 1, 2, 4, 8, and 16 weeds of each species per 7.5 m of row. Seed cotton yields decreased as a quadratic function of increasing weed density. One pigweed and one sicklepod plant per 7.5 m of row reduced yields by 9 and 9.7% in 1979 and 1980, respectively. At low levels of infestation (≤4 weeds/7.5 m of row), the competitive effect of pigweed and sicklepod was additive; however, at the high densities, the competitive effect was not additive. Mechanical harvesting efficiency and cotton maturity were not decreased by any weed density. Sicklepod was more competitive than pigweed in both years.

Cotton (Gossypium hirsutum L. ‘Westburn M’) was grown for 2 yr at two locations with full-season interference from buffalobur (Solanum rostratum Dunal ♯ SOLCU) at densities ranging from 0 to 64 plants/10 m of row. Dry weight of buffalobur harvested increased by 0.063 to 0.303 kg/plot for each additional weed/10 m of row. Intraspecific competition among buffalobur plants was observed at the higher weed densities. Cotton plant height was reduced by 16 and 32 buffalobur plants/10 m of row (or more) at Tipton and Perkins, OK, respectively, when compared with cotton grown under weed-free conditions. The threshold densities at which initial lint yield reductions occurred were 8 buffalobur plants/10 m of row in 1982 and 1983 at Tipton and 32 and 2 plants/10 m of row at Perkins in 1982 and 1983, respectively. Lint yields were reduced curvilinearly from 6 to 18 kg/ha for each additional buffalobur plant/10 m of row. Fiber quality was not significantly influenced by weed density when analyzed over all experiments; however, 50% span length, uniformity index, and micronaire were adversely affected in some environments.

Relationships between production of cotton (Gossypium birsutum L. ‘Westburn M’) and full-season interference from tumble pigweed (Amaranthus albus L. ♯ AMAAL) at densities ranging from 0 to 64 plants/10 m of row were measured in three replicated experiments in the field. Dry weight of harvested tumble pigweed increased by 0.149 to 0.402 kg/plot for each additional weed/10 m of row. Intraspecific competition among tumble pigweed plants was observed at the higher weed densities. Cotton plant height was reduced in all three experiments at the 32 or 64 weed densities, but harvesting difficulties were not encountered in these studies. The threshold density where initial lint yield reductions occurred ranged from 4 to 16 tumble pigweed plants/10 m of row in the three experiments. Lint yields were reduced from 8 to 11 kg/ha for each additional tumble pigweed plant/10 m of row. Interference from tumble pigweed did not significantly affect cotton fiber length, uniformity, strength, or micronaire of hand-harvested bolls.

Field studies were conducted on a Taloka silt loam (Mollic Albaqualf) to determine the effects of residual levels of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] on rice (Oryza sativa L.). Yield reductions could be overcome by increasing rice seeding rate, by decreasing seeding depth, or by applying the safeners CGA-43089 [α-(cyanomethoxyimino)-benzacetonitrile] or CGA-92194 [α-(1,3-dioxolan-2-yl-methoximino)-benzacetonitrile] to the rice seed. Greenhouse studies with the safeners and reduced seeding depths indicated that CGA-92194 was better than CGA-43089 for protecting rice from metolachlor injury, but reduced seeding depths did not reduce metolachlor injury.

Chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carboxyl]benzenesulfonamide} has recently been registered for the control of several broadleaf weeds in spring wheat (Triticum aestivum L.), durum wheat (Triticum durum Desf.), and barley (Hordeum vulgare L.) in western Canada. Residue carryover of this herbicide can cause injury to subsequent sensitive crops. A bioassay technique based on growth of pregerminated corn roots was used to detect levels of chlorsulfuron as low as 0.125 ppb in three Saskatchewan soils. Confidence levels of 95% were established. These confidence bands allowed the detection of chlorsulfuron levels within a minimum and maximum variation of 3.1 and 11.5% of root development.

Reaction of some wild oat (Avena fatua L. ♯4 AVEFA) populations to the herbicide triallate [S-(2,3,3-trichloroallyl)diisopropylthiocarbamate] was investigated in a controlled-environment chamber. Under specified conditions, 1.0 mg active ingredient of triallate incorporated in 1 kg of soil was a satisfactory diagnostic rate for 14-day-old seedlings. Five seedling growth parameters were studied. These parameters were emergence, survival to produce first leaf, mesocotyl length, first-leaf length, and seedling height. Of these, mesocotyl length was least affected by triallate treatment, and significant differences in variability for triallate reaction were found within and among historically triallate unexposed, as well as exposed populations. Within-population variation for seedling emergence and survival was higher in unexposed than in exposed populations. Populations with recurrent exposure to triallate were more tolerant to the herbicide under experimental conditions than historically unexposed populations. Triallate-tolerant lines were identified which were tolerant to two other common wild oat herbicides.

Foliage-only, soil-only, and foliage plus soil applications of picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), clopyralid (3,6-dichloro-2-pyridinecarboxylic acid), chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide}, and metsulfuron {2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoic acid} were used to determine the contribution of soil spray deposit to the control of Canada thistle [Cirsium arvense (L.) Scop. ♯ CIRAR] under greenhouse conditions. Herbicide reaching the soil contributed significantly to the suppression of secondary shoot growth, particularly when pots were watered from above. In subirrigated pots, the herbicides showed activity if they were sprayed on moist soil, but not if they were sprayed on dry soil. These results suggest that it is important to shield the soil during postemergence applications of herbicides in greenhouse experiments in order to avoid overestimating foliar activity.

Chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide} was nontoxic to safflower (Carthamus tinctorius L.) when applied postemergence in 1983 and 1984 at 0.018 and 0.035 kg ai/ha. Trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] at 1.1 and 1.7 kg ai/ha and pronamide [3,5-dichloro(N-1,1-dimethyl-2-propynyl)benzamide] at 0.8 and 1.1 kg ai/ha were applied previously as preplant soil-incorporated treatments. In both years, safflower was relatively free of weeds where trifluralin was applied alone or in sequential treatments with chlorsulfuron. Pronamide, with or without chlorsulfuron, failed to completely control witchgrass (Panicum capillare L. ♯ PANCA) in 1 yr; thus safflower grain yields were reduced 21 to 35% when compared to weed-free safflower. Chlorsulfuron controlled redroot pigweed (Amaranthus retroflexus L. ♯ AMARE), puncturevine (Tribulus terrestris L. ♯ TRBTE), and common sunflower (Helianthus annuus L. ♯ HELAN).

Eleven herbicide systems were evaluated from 1981 to 1983 for cotton (Gossypium hirsutum L. ‘Stoneville 825’) planted no-till directly into cover crops or winter fallow and for cotton planted following conventional tillage. Herbicide systems consisted of paraquat (1,1’-dimethyl-4,4’-bipyridinium ion) or glyphosate [N-(phosphonomethyl)glycine] and/or residual herbicides applied prior to crop emergence. Some systems also included early postemergence or postemergence-directed applications. Cover crops were crimson clover (Trifolium incarnatum L.), hairy vetch (Vicia villosa Roth.), and rye (Secale cereale L.). Soil cover in fallow treatments was comprised mainly of cotton stalk residue. Conventional tillage and seedbed preparation included fall moldboard plowing and spring disking/smoothing. Treatments were maintained in the same site each year. Order of cover crop susceptibility to herbicides applied prior to crop emergence was rye>clover>vetch. In 1981, all residual treatments except cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl]amino]-2-methylpropanenitrile} alone prior to crop emergence provided better than 80% control of annual weeds. In subsequent years only systems that included applications prior to crop emergence and postemergence-directed herbicides provided acceptable control. From 1981 to 1983, annual grasses increased 20- to 100-fold for systems in which control was poor. Weed control was generally superior in conventional tillage. Vetch adversely affected cotton stands in all 3 yr. Also, in 1982, reduced cotton stands resulted from cyanazine treatments applied prior to crop emergence in clover, vetch, and fallow. Cotton yields were affected by cover dessication, annual weed control, and cotton stands. Buildup of annual weeds reduced yields to near zero for some treatments in 1983.