Effects of propanil [N-(3,4-dichlorophenyl)propanamide] applied to three- to four-leaf rice (Oryza sativa L.) 1 or 7 days before, after, or tank mixed with methyl parathion (O,O-dimethyl-O-4-nitrophenyl phosphorothioate) were determined under different environmental conditions. Field experiments determined the effect on yield of drill-seeded rice, ‘Labelle’ for two planting dates in 1982 and ‘Lemont’ for one planting date in 1986. Treatments were applied at sunrise and at noon. Growth chamber and greenhouse experiments determined the effects of temperature, relative humidity (RH), and soil moisture on response of Labelle rice. In all experiments, propanil, both alone and with methyl parathion, resulted in 20 to 30% leaf burn during the first week after treatment with rapid recovery to less than 10% injury after 3 to 4 weeks. In field experiments, yields were not reduced in the treated rice below that in the untreated controls. In controlled-environment experiments, rice was not injured by propanil plus methyl parathion more than by propanil alone after 2 to 4 weeks. Both treated and untreated rice were injured more by the environmental conditions of high (40 C) temperature, low (40%) RH, and low (near the wilting point) soil moisture than by low (30 C) temperature, high (100%) RH, and flooded soil.

Studies were made of isozyme patterns of three enzymes and of total soluble proteins from seedlings of three crop species which were grown in association with different weed species. The gel electrofocusing separation technique was used. Marked qualitative and quantitative changes were observed in peroxidase of cabbage (Brassica oleracea L.) seedlings when grown in association with jimsonweed (Datura stramonium L.), velvetleaf (Abutilon theophrasti Medic.), wild mustard (Brassica kaber DC.), and green foxtail (Setaria viridis (L.) Beauv.). No differences were observed when lettuce (Lactuca sativa L.) and tomato (Lycopersicum esculentum Mill.) were grown in association with the above weed species. No differences were found in total soluble proteins or the isozyme patterns of esterase and acid phosphatase.

Aerial sprays of asulam (methyl sulfanilylcarbamate) applied at 3.4 or 6.7 kg/ha to forest plantations in western Oregon effectively controlled western bracken [Pteridium aquilinum (L.) Kuhn var. pubescens Underw.] without damaging Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings. Asulam also did not damage noble fir (Abies procera Rehd.) seedlings if applied without a surfactant. The half-life of asulam in forest soils ranged from less than 7 to 18 days and vertical movement in the soil profile was minimal. No herbicide residues were found in runoff water from treated areas up to 208 days after application.

Burs of common cocklebur (Xanthium strumarium L.) obtained from Stoneville, Mississippi; Urbana, Illinois; and Lamberton, Minnesota, were used in greenhouse and growth chamber studies. The Mississippi and the Illinois strains were both classified as being in the “strumarium” complex of X. strumarium, whereas, the Minnesota strain was classified as being in the “hybrid” complex. The Minnesota common cocklebur developed branch leaves in the leaf axils of the main stem to a much greater extent than did the Mississippi and Illinois common cocklebur. The Mississippi common cocklebur was frequently more tolerant of postemergence applications of bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] than were the Illinois and Minnesota common cockebur. The Mississippi and Illinois common cocklebur developed leaf necrosis when sprayed with an insecticide formulation containing malathion (o, o-dimethyl phosphorodithioate of mercaptosuccinate) and petroleum solvents; the Minnesota common cocklebur did not.

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.

Field experiments were conducted to determine optimum nozzle settings for applying glyphosate [N-(phosphonomethyl)glycine] in the recirculating sprayer for postemergence control of johnsongrass [Sorghum halepense (L.) Pers.] in soybeans [Glycine max (L.) Merr.]. Herbicide sprays were directed across the row to johnsongrass growing taller than soybeans in July and August. Herbicide not sprayed on johnsongrass was trapped and reused. Glyphosate at 0.56, 1.12, and 2.24 kg/ha applied with commercially available 25° spray nozzles provided johnsongrass control and soybean yields equal to those following applications with specialized uniform droplet nozzles. Glyphosate at 1.7 kg/ha applied in the recirculating sprayer using only one nozzle per row provided control of johnsongrass equal to or better than that from applications made with two, three, or four nozzles per row. Soybean yield following application of glyphosate at 1.7 kg/ha with one nozzle per row was equal to yields obtained following its application with two, three, or four nozzles per row, with or without surfactant at 0.1% in spray solutions. Soybean yield was higher with four nozzles per row than with one nozzle per row when 0.5% surfactant was included in spray solutions. Soybean injury was lower and yield was higher when glyphosate was applied in the recirculating sprayer rather than over-the-top with a conventional sprayer. Glyphosate at 1.12 kg/ha applied in the recirculating sprayer caused more injury to ‘Hill’ and ‘Bragg’ than to ‘Forrest’ or ‘Tracy’ soybeans.

Interspecific crosses were made between perennial sowthistle (Sonchus arvensis L.) and annual sowthistle (Sonchus oleraceus L.). Flower head size, leaf type, and creeping root growth of the hybrid were intermediate to those same morphological characteristics of the parents. Backcrosses to the parents produced plants which resembled annual or perennial sowthistle more closely than did the F1 hybrids. Annual sowthistle and backcrosses to annual sowthistle were more tolerant to (2,4-dichlorophenoxy)acetic acid (2,4-D) and 3,6-dichloro-o-anisic acid (dicamba) than were perennial sowthistle or backcrosses to perennial sowthistle. However, annual and perennial sowthistle were similar to each other in response to 4-amino-3,5,6-trichloropicolinic acid (picloram). Natural crosses between annual and perennial sowthistles may account for some of the variability in herbicide response found in perennial sowthistle.

Wheat (Triticum aestivum, subspecies vulgare L.) straw, sawdust, peat, and cellulose pulp were mixed with Westmoreland silt loam in a 2 to 1 ratio (soil to organic matter) in a greenhouse study, on the influence of organic matter-interaction with 3-amino-2,5-dichlorobenzoic acid (amiben) on nodulation and growth of soybeans (Glycine max L., var. Clark). The dry weights of shoots and roots, harvested 1 week after flower initiation in the control, decreased with increasing rates of amiben in the unamended soil and in soil in which cellulose pulp and peat were mixed.

Downy brome (Bromus tectorum L.) is a widely distributed invasive winter annual grass across western North America. Bromus tectorum phenology can vary considerably among populations, and those differences are considered adaptively significant. A consensus hypothesis in the literature attributes the majority of observed differences in B. tectorum phenology to differing vernalization requirements among populations. A series of greenhouse experiments were conducted to identify differences in B. tectorum vernalization requirements and link vernalization to expression of annual false-brome [Brachypodium distachyon (L.) P. Beauv.]-derived vernalization gene homolog (BdVRN1). Results from this study indicate that variation in time to flowering is partially governed by differing vernalization requirements and that flowering is linked to the expression of BdVRN1.

Research was conducted in soybean and common cocklebur to determine if the synergistic interactions of clomazone plus metribuzin and clomazone plus linuron were due to the effect of one herbicide on root uptake, partitioning, or metabolism of the other. Treatments consisted of 14C-clomazone alone and combined with metribuzin or linuron, 14C-metribuzin alone and combined with clomazone, and 14C-linuron alone and combined with clomazone. Root uptake and partitioning of clomazone applied alone in soybean differed compared to clomazone plus metribuzin. Root uptake and partitioning of metribuzin or linuron did not differ when applied alone or combined with clomazone. Binding of clomazone or its metabolites in an unextractable form may be a method of deactivating clomazone by soybean, but not by common cocklebur. Levels of parent clomazone were higher in common cocklebur roots when clomazone was combined with metribuzin and linuron compared to clomazone done. Levels of parent metribuzin were higher in soybean roots, and in common cocklebur roots and shoots when clomazone was combined with metribuzin compared to metribuzin alone. Levels of parent linuron were greater in soybean shoots when linuron was applied with clomazone compared to linuron alone. These results indicate that the metabolism of metribuzin and linuron is altered in both species when clomazone is applied, leading to increased phytotoxicity.

Foliar-spray and radioisotope herbicidal studies were conducted near Tucson, Arizona, to study factors influencing absorption, translocation and toxicity of (2,4,5-trichlorophenoxy)acetic acid (2,4,5-T) in creosotebush [Larrea tridentata (DC.)Cov.]. Maximum absorption and translocation of 14C-labeled 2,4,5-T occurred approximately 30 days after initiation of effective summer rains and coincided with maximum total killing of creosotebush. This occurred during the full-flowering to mid-fruiting stage of phenological development, overlapped the period of old leaf drop, and was due in part to the generally greater basipetal translocation of radioactive 2,4,5-T from old leaves, flowers, fruits, and young bark than from young leaves. Translocation of radioactive 2,4,5-T was relatively slow, 1 to 5 cm per hour, and basipetal movement ceased after 18 to 24 hr, following which the 2,4,5-T largely disappeared from the vascular tissues of the stem. Absorption of 2,4,5-T by the leaves was low during dormancy and may have limited herbicidal effects during this period, but it was not a factor during the season of high susceptibility.

Simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), and a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) were evaluated for weed control in pecan (Carya illinoensis (Wang.) K. Koch) orchard establishment. Maximum weed control and tree growth occurred in plots treated with diuron and simazine applied at 3.0 and 4.0 lb/A, respectively. During the second year, phytotoxic symptoms were observed in plots which had received superimposed annual treatments of diuron at 3.0 lb/A, but none appeared in simazine or trifluralin plots.

Foliar applications of 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) at 0.05 to 1.0 lb/A caused characteristic injury symptoms on cucumber (Cucumis sativus L.) plants. Analytical methods were evaluated and found suitable in detecting atrazine in cucumber leaves sprayed at a low rate of 0.005 lb/A. For analytical detection, tissue samples should be taken as soon as necrotic symptoms appear, 4 to 7 days after suspected drift, and frozen immediately.

Fluorochloridone {3-chloro-4-(chloromethyl)-1-[3-(trifluoromethyl)phenyl]-2-pyrrolidinone} effectively controlled wild mustard (Sinapis arvensis L. # SINAR) in sunflowers (Helianthus annuus L. ‘Hybrid 894′). Preemergence (pre) treatments were more effective than preplant-incorporated (ppi) treatments at rates of 0.3 to 1.1 kg ai/ha. Applied as a foliar spray, fluorochloridone at rates of 0.12 to 0.25 kg ai/ha controlled 96% or more of wild mustard but some crop injury occurred. When fluorochloridone was mixed with trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] or EPTC (S-ethyl dipropyl carbamothioate) and applied ppi, several annual grasses as well as wild mustard were controlled.

Paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), 2,4-D [2,4-dichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), and 2,4-D plus dicamba were applied as postemergence herbicide treatments in two experiments to weed-free dormant bermudagrass [Cynodon dactylon (L.) ♯3 CYNDA] turf in the Piedmont region of Georgia. Herbicides were applied as a split application to separate plots on February 2 plus February 16 and February 16 plus March 3 (± 4 days) on four bermudagrass cultivars (‘Tifway’, ‘Tifgreen’, ‘Tifdwarf’, and ‘Ormond’) in one experiment and to Tifway with vertical mowing treatments for thatch removal in a second experiment. In 2 of 3 years, paraquat applied to dormant turf in February delayed growth of bermudagrass in April. The growth of Tifway and Tifdwarf was retarded more from paraquat at 1.2 kg ai/ha in one year than Tifgreen or Ormond. Dicamba applied alone or with 2,4-D delayed turf growth in early spring more than did 2,4-D alone. In thatch-free turf, selected treatments of paraquat, dicamba, and 2,4-D plus dicamba also delayed spring growth of bermudagrass more than did 2,4-D.

Dicamba (3,6-dichloro-o-anisic acid), 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], 3,6-dichloropicolinic acid, picloram (4-amino-3,5,6-trichloropicolinic acid), triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] were applied at rates of 0.3, 0.6, 1.1, and 2.2 kg/ha pre- and postemergence to greenhouse-grown common buffelgrass (Cenchrus ciliaris L. ♯3 PESCI). Buffelgrass tolerated preemergence sprays of 3,6-dichloropicolinic acid up to and including 1.1 kg/ha. All other treatments except picloram and 2,4,5-T at 0.3 kg/ha were phytotoxic to emerging buffelgrass. Buffelgrass tolerated early postemergence applications of 2,4-D, picloram, and tebuthiuron at 0.3 kg/ha; dicamba and 2,4,5-T at 0.6 kg/ha; and 3,6-dichloropicolinic acid at 2.2 kg/ha based on oven-dry shoot production 1 month after treatment. Regrowth of buffelgrass from stubble 1 month after original harvest of the early postemergence treatment occurred only with all rates of 3,6-dichloropicolinic acid and 2,4,5-T at 0.3 kg/ha. When treated at 45 days after planting, buffelgrass tolerated dicamba, 2,4-D, 2,4,5-T, 3,6-dichloropicolinic acid, and picloram at 2.2 kg/ha, but top growth production was significantly reduced by most rates of hexazinone and tebuthiuron. Relative differences in regrowth of buffelgrass 1 month after the original harvest were similar to those of the original harvest. Mature buffelgrass (90 or 150 days old) responded similarly to herbicides as the 45-day-old buffelgrass.

Gibberellin-enhanced response of bean plants (Phaseolus vulgaris L. ‘Black Valentine’) and Canada thistle [Cirsium arvense (L.) Scop.] to bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] and glyphosate [N-(phosphonomethyl)glycine] was determined on both species under controlled photoperiods in the growth chamber and on Canada thistle under natural conditions in the field. Pretreatment of bean plants in the growth chamber with 10 mg/L gibberellin (GA3 or GA4/7) more than doubled the herbicidal effect of 1600 mg/L bentazon treatments. Pretreatment of Canada thistle plants in the growth chamber with 100 mg/L GA4/7 increased the herbicidal effect of 50 mg/L bentazon applications more than four-fold, and that of 400 mg/L glyphosate applications by more than two-fold. The phytotoxicity of bentazon to field-grown Canada thistle increased 10% or more in populations pretreated with 25 g/ha gibberellin; and that of 840 g/ha glyphosate was similarly increased. The effectiveness of a higher glyphosate dosage (1680 g/ha) was not significantly increased by GA pretreatment. Plants induced to bolt with gibberellin (GA4/7) were injured more by bentazon than were plants that bolted naturally.

Response of weeds and sugarbeets (Beta vulgaris L. ‘Mono Hy D2′) to preplanting treatments of mixtures of cycloate (S-ethyl N-ethylthiocyclohexanecarbamate) and ethofumesate [(±)-2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate] was evaluated in five field studies. A mixture containing 1.7 kg/ha of each herbicide reduced the stand of common lambsquarters (Chenopodium album L.) 90%, green foxtail [Setaria viridis (L.) Beauv.] and yellow foxtail [Setaria lutescens (Weigel) Hubb.] 97 to 99%, kochia [Kochia scoparia (L.) Schrad.] 64 to 77%, and redroot pigweed (Amaranthus retroflexus L.) 82 to 99%. The response of weeds to preplanting applications of mixtures of cycloate and ethofumesate was independent of soil texture, whereas response of sugarbeets was dependent on soil texture. The herbicide mixtures significantly reduced the pre-thinning stand of sugarbeets and root and sucrose yields on two sandy loams, but not on a clay loam.

A new method was developed for incorporating herbicides into the root zone of saltcedar (Tamarix pentandra Pall.) in arid, low rainfall areas. A spray pipe with five nozzles was mounted along the rear edge of a 2.44-m root plow blade. A supply line connected the spray pipe with a sprayer mounted on the plow frame. In operation, the saltcedar roots were severed at a selected depth by the blade as herbicide was sprayed simultaneously into the cut-root zone. A similar root plow with a 1.22-m blade was designed for use on small research plots.

In the rapid response (RR) biotype of glyphosate-resistant (GR) giant ragweed (Ambrosia trifida L.), exposure to glyphosate elicits H2O2 production in mature leaves, resulting in foliage loss and reduced glyphosate translocation. When glyphosate is applied with POST herbicides intended to improve control of A. trifida, the RR to glyphosate has the propensity to antagonize these herbicide combinations. This research documents how transient changes in air temperature, soil moisture, and light intensity during a 6-d period surrounding herbicide application regulate induction of the RR and the effect on POST herbicide interactions with glyphosate. Air temperature had the greatest influence on H2O2 accumulation in leaf disks following treatment with glyphosate, as plants at 30 C produced more than twice the amount of H2O2 at 2.5 h after treatment compared with 10 C. Plants under field capacity conditions accumulated nearly 50% more H2O2 than those at one-third field capacity, while those under no shade had only 18% more H2O2 compared with those in a shaded environment. Despite these initial results, dry weight reduction at 21 d after treatment never differed by more than 8% between levels of environmental factors, thus indicating a negligible influence on glyphosate efficacy. The magnitude of glyphosate-induced antagonism was generally greater at 30 C (12% to 21% less than expected control) versus 10 C (11% to 16%) on atrazine, cloransulam, dicamba, and topramezone and was greater at field capacity (20% to 24%) versus one-third field capacity (11% to 15%) on cloransulam and topramezone. These results indicate air temperatures and soil moisture levels conducive to optimal plant growth accelerate the RR to glyphosate, thereby increasing the likelihood of glyphosate-induced antagonism on several translocated herbicides.