Field and growth chamber experiments were conducted to determine the effects of surface soil moisture on the phytotoxicity of alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] to grain sorghum [Sorghum bicolor (L.) Moench. ‘Funk 623 GBR’], which was unprotected or protected with CGA-43089 {α-[(cyanomethoxy)imino] benzeneacetonitrile}. In field tests, neither alachlor nor metolachlor was phytotoxic to unprotected grain sorghum when the surface soil remained dry until the sorghum had emerged. CGA-43089 protected sorghum emerging from moist soil that had been treated with alachlor or metolachlor at rates of 2.24 or 3.36 kg/ha. Growth chamber tests showed that CGA-43089 was less effective in protecting sorghum from herbicide injury when Ships clay was continuously wet [110% field capacity (FC)] from time of planting to emergence (3 to 5 days) than when soil was wet for only 1 or 2 days prior to emergence. In contrast, if the surface soil remained dry until the coleoptile reached the soil surface, alachlor and metolachlor had little effect on sorghum even when no protectant was present. When sorghum was planted in Arenosa sand containing 5% organic matter, protected sorghum grew as well as the control even under continuous high moisture conditions. Metolachlor incorporated into the root zone at a rate of 20 ppm had no effect on either protected or unprotected sorghum. Alachlor and metolachlor were most phytotoxic when placed in the surface 1.25 cm of moist soil or when incorporated. The coleoptile was the most susceptible plant part. Thus, the key to grain sorghum response to these herbicides was in herbicide placement and availability to the coleoptile. Under conditions normally leading to phytotoxic effects from alachlor or metolachlor, grain sorghum growth was significantly better from seed protected with CGA-43089 than from unprotected seed.

Absorption, translocation, and metabolism of foliar-applied ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulphonate] were studied to explain field observations showing differences in susceptibility among sugarbeet (Beta vulgaris L.), common ragweed (Ambrosia artemisiifolia L.), redroot pigweed (Amaranthus retroflexus L.), and common lambsquarters (Chenopodium album L.). In laboratory studies, two- to four-leaf seedlings of the highly susceptible species, redroot pigweed and common lambsquarter, absorbed greater amounts of 14C-ethofumesate from foliar application than the moderately susceptible common ragweed and tolerant sugarbeet. Sugarbeet translocated very little 14C from treated foliage to untreated plant tissue. All weed species translocated 14C-ethofumesate to untreated leaf tissue when 14C-ethofumesate was applied to seedlings at the two-leaf stage. Ethofumesate was translocated basipetally to the stem and root of two-leaf redroot pigweed and common lambsquarter seedlings. A high percentage of the 14C was found in the water-soluble fraction in sugarbeet seedlings, indicating inactivation. The amount of metabolites recovered in the non-polar fraction depended on the stage of plant growth. Total photosynthesis and respiration in redroot pigweed was inhibited 4 h after foliar application and did not recover after 96 h. Uptake and evolution of CO2 were also inhibited in sugarbeet leaves, but they recovered rapidly, depending on age of plant at treatment. The stage of plant development was the key factor determining species response to foliar treatments of ethofumesate in terms of absorption, metabolism, and total photosynthesis and respiration.

A phytosociological study of weeds carried out at Ajmer in the semi-arid zone of India revealed the presence of Dactyloctenium-Cynodon-Chloris community during the monsoon season and Cynodon-Tribulus-Tephrosia community of weeds during the summer season, growing on coarse and sandy soils and in harmony with all biotic factors. The communities experience high summer and low winter temperatures with rainfall occurring only during the monsoon season (July to September). Other dominant weeds included Achyranthes aspera L., Amaranthus gracilis Desf., Tephrosia purpurea (L.) Pers., and Trianthema portulacastrum L. during the monsoon season, and Boerhavia diffusa L., Indigofera linifolia (L.) Retz., and Rhus mysurensis Heyne ex Wight. are dormant during the summer season.

Bromacil (5-bromo-3-sec-butyl-6-methyluracil), glyphosate (N-phosphonomethylglycine), picloram (4-amino-3,5,6-trichloropicolinic acid), simazine [2-chloro-4,6-bis (ethylamino)-s-triazine], and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] were evaluated at four application rates and five application dates, May 1, June 1, July 1, August 1, and September 1, for their ability to control seven herbaceous, forest ground covers, hayscented fern (Dennstaedtia punctilobula (Michx.) Moore), New York fern (Thelypteris noveboracensis L.), short husk grass (Brachyelytrum erectum Schreb.), bracken fern [Pteridium aquilinum (L.) Kuhn var. latiusculum (Desv.) Underw.], wild oat grass (Danthonia compressa Aust.), rough goldenrod (Solidago rugosa Mill.), and flattop aster (Aster umbellatus Mill.) without residual effects on black cherry (Prunus serotina Ehrh.) seed stored in the forest floor, or on survival and growth of natural or planted black cherry seedlings. Control of most of the target species depended on the date and rate of application. Simazine had no herbicidal effect on these extremely acid (pH 3.9 to 4.4) Allegheny Plateau sites. None of the herbicides interfered with germination of black cherry seed stored in the forest floor or with establishment of seedlings. Bromacil applied at 22.4 kg/ha, picloram, at 9.0 kg/ha, and hexazinone at 13.4 kg/ha reduced survival, or growth, or both, of black cherry seedlings planted in a forest opening. Glyphosate was the most economical herbicide that met the control criteria. Application of 1.1 kg/ha between August 1 and September 1 produced acceptable control of all target species for at least 3 yr.

Information from taxonomic treatments and comparisons of accessions from numerous locations grown in the field and greenhouse were combined and summarized to produce a key and descriptions of common agricultural nightshades in North America (Solanum americanum Mill., S. nigrum L., S. ptycanthum Dun., and S. sarrachoides Sendt.). Quantitative and qualitative descriptions of key characters and photographs of important morphological structures are provided to facilitate field identification. Problems with nomenclature among these species are discussed, and a system of common names that would standardize usage is proposed.

Field studies of herbicidal antagonism were conducted in corn (Zea mays L.), soybeans (Glycine max L. Merr.), and on industrial sites. The addition of chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea], cyanazine {2-[[4-(chloro-6-(ethylamino)-s-triazin-2-yl] amino]-2-methylpropionitrile}, bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate], or atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] wettable powder plus dicamba (3,6-dichloro-o-anisic acid) to glyphosate [N-(phosphonomethyl)glycine]-alachlor[2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] combinations reduced the activity of glyphosate on quackgrass [Agropyron repens (L.) Beauv.], common dandelion (Taraxacum officinale Weber), and Canada thistle [Cirsium arvense (L.) Scop.] in no-till corn. Reduced weed control from antagonism resulted in decreased corn yields. Linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], chlorbromuron, or metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one], when added to glyphosate, reduced the control of quackgrass but not that of Canada thistle, alfalfa, or common dandelion in soybeans. Antagonsim was not evident in annual weed species. In perennial weeds, the degree of antagonism was often reduced with increased dosages of glyphosate. The inclusion of terbacil (3-tert-butyl-5-chloro-6-methyluracil), bromacil (5-bromo-3-sec-butyl-6-methyluracil), and simazine [2-chloro-4,6-bis(ethylamino)-s-triazine] with glyphosate in mixes interfered with the control of smooth brome (Bromus inermis Leyss.), but not when applications of the residual herbicides were delayed. Quackgrass control was reduced when amitrole (3-amino-s-triazole) was mixed with glyphosate, or when applied separately.

Toxicity of non-radiolabeled and absorption and translocation of 14C-activity of applied 14C-acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} in showy crotalaria (Crotalaria spectabilis Roth) were evaluated in the growth chamber at air temperatures of 18, 27, or 35 C and 40 or 100% relative humidity (RH). Four days after treatment, acifluorfen applied over-the-top at 0.1 kg/ha resulted in 64 to 95% injury, but did not kill showy crotalaria. Acifluorfen was more toxic at 100% than at 40% RH. At either 40 or 100% RH, acifluorfen was more toxic at 27 and 35 C than at 18 C. Plants were placed in the greenhouse 4 days after treatment. At 6 weeks after treatment, there was extensive regrowth, and injury to all plants was less than 32%, except for those plants initially treated at 18 C and 40% RH for 4 days. These plants showed 76% injury. Acifluorfen applied to a single leaf midway up the stem caused 80 to 100% injury to the immature leaves near the apex, but less than 30% injury to lower leaves. Absorption of 14C-activity from 14C-acifluorfen applied to a single leaf midway up the shoot varied from 8 to 76% after 2 days. At either 40 or 100% RH, absorption was approximately four-fold greater at 27 and 35 C than at 18 C. At all temperatures tested, absorption was three- to four-fold greater at 100% than at 40% RH.

The absorption, translocation, and exudation of 14C-glyphosate [N-(phosphonomethyl) glycine], 14C-fosamine [ethyl hydrogen (aminocarbonyl)phosphonate] and 14C-amitrole (3-amino-s-triazole) in field horsetail (Equisetum arvense L.) were examined in glasshouse experiments. Amitrole was absorbed much more readily than either fosamine or glyphosate, and although the initial translocation of amitrole was faster, eventually more 14C was recovered from the underground parts of plants treated with 14C-glyphosate and fosamine. Radioactivity from all three compounds was translocated to areas of meristematic activity such as shoot and rhizome apices and rhizome nodes. The amounts of radioactivity recovered from the roots and rhizomes were small in relation to the amounts applied. Root exudation and guttation could account for some loss of herbicide from the plant. Radioactivity from 14C-amitrole, in particular, was present in relatively large amounts in guttation fluid.

Field research was conducted in 1973, 1974, 1977, and 1978 to compare water-culture practices and rates of molinate (S-ethyl hexahydro-1H-azepine-1-carbothioate) for control of “strawhull” red rice (Oryza sativa L.) in water-seeded rice (O. sativa L.). Water-culture treatments (continuously drained, alternately drained and flooded, or continuously flooded during the first 28 days after seeding) alone, or preplant, soil-incorporated treatments of molinate (3.4, 4.5, and 6.7 kg/ha) alone did not control red rice. Treatments of preplant-incorporated molinate at 4.5 and 6.7 kg/ha in a continuously flooded culture or 6.7 kg/ha in an alternately drained-flooded culture controlled 87 to 93% of the red rice and permitted production of satisfactory yields of high quality rice grain.

Glyphosate [N-(phosphonomethyl)glycine] was applied at various stages of maturity to corn (Zea mays L. ‘Pioneer brand 3147’ and ‘Dekalb XL 394’), soybeans [Glycine max (L.) Merr. ‘Forrest’ and ‘Essex’], and johnsongrass [Sorghum halepense (L.) Pers.]. Glyphosate applied over-the-top of corn before the grain moisture level decreased to 30% (black layer will have been formed) caused various seed and subsequent progeny abnormalities. Depending on grain moisture level at the time of glyphosate application, seed weight was sometimes reduced and progeny seedling emergence, vigor, and weight were reduced. Also, abnormal seedlings, albino or straited, occurred. Glyphosate applied 2½ weeks or more before soybean maturity reduced seed weight, caused seed discoloration, and drastically reduced progeny seedling emergence, vigor, and weight. Glyphosate applied in September or early October controlled semimature johnsongrass. Later applications were less effective because of advanced senescence.

Field experiments were conducted in 1977 and 1978 to determine susceptibility of rhizome johnsongrass [Sorghum halepense (L.) Pers.] to metriflufen3 {2-[4-(4-trifluoromethylphenoxy) phenoxy] propanoic acid, methyl ester} applied as preplant-incorporated, preemergence, or postemergence treatments. Rates of metriflufen applied preplant incorporated and preemergence were 1.12, 2.24, and 3.36 kg/ha. Postemergence treatments consisted of 0.56, 1.12, and 1.68 kg/ha of metriflufen plus a non-ionic polyethylene glycol alkyl ester, each applied to johnsongrass at growth stages of 30 to 38 cm, 60 to 75 cm, and heading. Johnsongrass control increased with each increase in rate of soil-applied metriflufen with no differences in control between preplant incorporated and preemergence treatments. Johnsongrass density was reduced by increased rates of metriflufen, and 1978 soil-applied treatments reduced densities by 62%. Preplant-incorporated and preemergence applications of 3.36 kg/ha of metriflufen resulted in higher soybean yields than did the two lower rates. Results from treatments with trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) were similar to those with metriflufen at the same rate. Metriflufen applied to 30-to 38-cm johnsongrass reduced stands by 60% in 1978, but stands increased by 51 and 71% in plots treated at the 60- to 75-cm or heading stages of growth. Soybean tolerance to postemergence applications of metriflufen was excellent for all stages of growth and rates of metriflufen.

Postemergence applications of MSMA (monosodium methanearsonate) for weed control in spring wheat (Triticum aestivum L.) were evaluated in the field, greenhouse, and controlled environmental chamber. MSMA controlled weeds better when applied to wheat at the four- to five-leaf stage than when applied at the two- to three-leaf stage. MSMA, tank mixed with barban (4-chloro-2-butynyl-m-chlorocarbanilate) or diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}, controlled wild oat (Avena fatua L.), green foxtail, [Setaria viridis (L.) Beauv.] and broadleaf weeds better than did MSMA applied alone. Wild oat control with tank-mix applications of MSMA and difenzoquat (1,2-dimethyl-3,5-diphenyl-1H-pyrazolium) was variable. Weed control with MSMA was enhanced by 30 C air temperatures, 90% relative humidity, and adequate soil moisture. A simulated rainfall of 0.5 mm within 0.5 h or 4 mm with 4 hr after application reduced wild oat control with MSMA.

The effect of postharvest storage temperature (–15, 5, 20, and 30 C) on seed dormancy of red rice [Oryza sativa L. ‘strawhulled (SH)’], an annual species, was studied. Intact and dehulled (by hand) seeds were dormant at harvest. Intact seeds were nondormant (greater than 90% germination at 30 C) after dry storage at 20 or 30 C for 4 weeks after harvest. In intact seeds stored dry at 5 C, the degree of dormancy was dependent upon postharvest exposure time at 20 C prior to storage. Dormancy of intact seeds decreased at 5 C as this initial postharvest exposure to 20 C was increased from 2 to 7 days. This effect of initial 20 C exposure was independent of seed moisture content (11 to 12%). After dry storage of intact seeds at 5 C, dehulling promoted germination. Germination of such dehulled seeds increased with increasing storage time at 5 C up to 11 months when complete germination occurred. The response of seeds dehulled immediately after dry storage at 5 C was independent of prior exposure time (2 to 7 days) at 20 C. Storage at −15 C prevented all forms of dry-afterripening for 1 yr.

Field and laboratory experiments were conducted in 1977 and 1978 to evaluate the movement and persistence in soil of metriflufen {methyl ester of 2-[4-(4-trifluoromethylphenoxy)phenoxy] propanoic acid} under different conditions. In the field, delaying incorporation of metriflufen did not affect its activity in Taloka silt loam for either year as shown by bioassay with grain sorghum [Sorghum bicolor (L.) Moench]. Metriflufen activity in the soil persisted for 63 and 40 days after application in 1977 and 1978, respectively. In the laboratory, metriflufen moved through saturated soil columns to an average depth of 7.5 and 18.5 cm following the addition of 2.5 or 10 cm of water to the columns. In a growth chamber bioassay, grain sorghum growth in treated soil gave a dose-response in a range of 0.02 ppmw (I10), 0.09 ppmw (I50), and 0.38 ppmw (I90). When soil treated with metriflufen at 1 ppmw was incubated for specified times under soil moisture levels of 5, 15, or 25% and temperature regimes of 15, 25, or 35 C, soil incubated at 15 C for as long as 75 days completely inhibited grain sorghum growth regardless of the other treatment variables. Grain sorghum growth inhibition was reduced with incubation time and warmer temperatures for treated soil maintained at 5 and 15% moisture, but sorghum growth inhibition persisted for treated soil incubated under wet (25% moisture) conditions.

The field performance of amitrole (3-amino-s-triazole) formulations containing a number of additives was tested on bracken [Pteridium aquilinum (L.) Kuhn var. aquilinum]. All formulations that did not contain thiocyanate produced severe foliar scorching within 72 h of spraying. The following season, control was relatively poor (63 to 77% reductions in frond density). The formulation of amitrole with sodium iodide produced particularly severe scorching followed by a nonsignificant reduction in frond density (2%) the following season. Formulations containing ammonium thiocyanate (molar ratios of 1:0.5, 1:0.75, 1:1, and 1:1.25 amitrole:ammonium thiocyanate) greatly reduced this foliar scorching, and control the following season was of the order of 94 to 97% in all cases. Translocation was proposed as being the limiting factor in control, ammonium thiocyanate increasing translocation by preventing scorching and hence decreasing decomposition in the foliage. To investigate scorching further, a bioassay, which consisted of floating bracken leaflets on amitrole solutions, was developed. The commercial 1:1 molar ratio of amitrole:ammonium thiocyanate may not be optimum for all conditions. Other additives were tested and cyanide and hexacyanoferrate (II) were found to be very active scorch inhibitors.

Experiments were conducted in the field, greenhouse, and controlled environment chambers to determine the extent to which MCPA {[(4-chloro-o-tolyl)oxy] acetic acid} antagonizes wild oat (Avena fatua L.) control with diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}. Wild oat control with diclofop at 1 kg/ha was reduced from 96% when used alone to 76, 48, 31, and 14% by tank mixture with IAA (3-indole acetic acid), MCPA, 2,4-D [(2,4-dichlorophenoxy)acetic acid], or dicamba (3,6-dichloro-o-anisic acid), respectively. Wild oat control with diclofop applied alone at 1.1 kg/ha was similar to that of diclofop at 2.2 kg/ha applied as a tank mixture with MCPA at 0.15 or 0.3 kg/ha. MCPA antagonism of wild oat control with diclofop increased as the post-treatment temperature increased from 10 to 30 C. MCPA antagonism of wild oat control with diclofop was the same whether the herbicides were applied to the foliage only or to the foliage and soil. Approximately 20% of the wild oat root inhibition with diclofop applied postemergence, however, was from diclofop uptake from the soil. MCPA at 0.6 kg/ha did not reduce wild oat control when applied as a sequential treatment 2 days before or 1 day after diclofop at 1.1 kg/ha.

The effects of weed density on the phytotoxicity of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] to white mustard (Brassica hirta Moench) and alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] to foxtail millet [Setaria italica (L.) Beauv.] were determined in the greenhouse. The fresh weight of both plants was reduced by the herbicide treatments, but as the weed density (plants per pot) increased, the herbicide rate required to cause equivalent fresh weight reductions per pot also increased. White mustard and foxtail millet grown in pots absorbed less 14C-atrazine or 14C-alachlor per plant from the soil at high weed density than low, regardless of herbicide rate. Foxtail millet seedlings grown in petri dishes absorbed less 14C-alachlor per plant from aqueous solution as the number of seedlings per petri dish increased. Data from field experiments in 1977 and 1979 indicated that more alachlor or metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl) acetamide] was required for equal control of a high than low density of forage sorghum [Sorghum bicolor (L.) Moench ‘Rox Orange’] interseeded in maize (Zea mays L.). Rox Orange sorghum was used to simulate shattercane [Sorghum bicolor (L.) Moench], a problem weed in Nebraska. At the higher Rox Orange sorghum seeding rate used, both alachlor and metolachlor treatments decreased Rox Orange sorghum plant populations but not yield.

Photosynthesis in corn (Zea mays L. ‘Pioneer 3369A’) was inhibited 25% by atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] after a 2-h root exposure in nutrient solution. Photosynthesis of the treated plants had completely recovered 21.4 h after removal from the treatment solution. Recovery of photosynthesis from second and third successive atrazine treatments required only 10.3 h and 4.0 h, respectively. Atrazine metabolism rates in corn plants after 1, 2, or 3 successive 4-h treatment periods, where each treatment period was followed by a 12-h recovery period, showed increased rates of metabolism of atrazine during each recovery time. An increased level of glutathione-S-atrazine was found following the first 4-h atrazine treatment and 12-h recovery. The enhanced production of GS-atrazine was maintained throughout subsequent exposures and recoveries. An inverse correlation (r2 = 0.992) was found between the increase in GS-atrazine production following each 4-h atrazine exposure and the time required for corn plants to recover from atrazine-induced photosynthesis inhibition. Enhanced detoxification of atrazine by corn plants pretreated with atrazine was indicated. No enhanced tolerance to other herbicides was observed from atrazine pretreatment. This phenomenon is similar to that described for the enhanced detoxification of several insecticides in animal systems.

The newly developed herbicide buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadizol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone} was studied with respect to its interaction with soils and homoionic clay minerals and its response to irradiation with ultraviolet light. Results showed that it could enter the interlamellar spaces of swelling clays such as smectite. Isothermic adsorption studies indicated that Cu+2-smectite adsorbed more buthidazole than Cu+2-kaolinite. The Cu+2-clay adsorption isotherm fitted the Langmuir model. The effect of exchangeable cations on adsorption was not significant in soils of high organic matter content. Bioassay studies indicated that buthidazole's phytotoxicity was not decreased in either clays or in organic soils. Infrared spectroscopic studies showed the coordination of buthidazole with Cu+2 through C=O Cu interaction with buthidazole resulted in a ligand-to-metal ratio to 1:1. Protonation of buthidazole occurred in Al+3-and H+-smectite. The herbicide was labile to UV-light irradiation at 254 nm but not at 366 nm. The photoconversion indicated a first-order reaction. The photolytic product(s) included the –N=C=O structure. Copper(II) ions, which form complexes, retarded photolysis of buthidazole in UV-light, but the Ca+2 ion, which is unable to form complexes, did not.

Several regimes of supplying exogenous aromatic amino acids to intact, 3-day-old, soybean [Glycine max (L.) Merr. ‘Hill’] seedlings by root uptake were tested to determine if growth retardation caused by root-fed, 0.5 mM glyphosate [N-(phosphonomethyl) glycine] could be reversed. Generally, root-fed levels of aromatic amino acids just below growth-retarding levels (e.g. 1 mM phenylalanine + 0.1 mM tyrosine) reversed root growth inhibition caused by glyphosate to a small (ca. 10%) but significant extent. Feeding aromatic amino acids for 1 to 3 days before glyphosate exposure did not enhance the reversal. Uptake and metabolism of root-fed, aromatic amino acids in control and glyphosate-treated plants were verified by increased levels of hydroxyphenolic compounds (end products of aromatic amino acid metabolism) and by uptake and incorporation of 14C-labeled phenylalanine and tyrosine. On a fresh weight basis, glyphosate had no inhibitory effect on uptake or incorporation of these amino acids into protein or secondary phenolic compounds. After 3 days of exposure, glyphosate had no substantial effects on shikimate dehydrogenase activity in control or aromatic amino acid-fed seedlings. These data suggest that either root-fed aromatic amino acids are compartmentalized differently than the endogenous pools affected by glyphosate or that root-fed glyphosate exerts most of its effect on growth of soybean seedlings through means other than inhibition of aromatic amino acid synthesis.