In greenhouse and growth-chamber studies, increasing the level of either light or temperature increased bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] phytotoxicity to cucumber (Cucumis sativus L.). Light had a greater influence on phytotoxicity than did temperature. Light and temperature conditions after bentazon application had a greater influence on phytotoxicity than did light and temperature conditions before application. Maximum phytotoxicity was obtained from treatment with low light level before application and high light level after application.

‘Wilmington’ and ‘Pensacola’ cultivars of bahiagrass (Paspalum notatum Flügge) were found to exhibit a differential level of tolerance to certain triazine herbicides. Pensacola was more susceptible to postemergence treatments of atrazine [2 - chloro - 4 - (ethylamino) - 6 - (isopropylamino) -s - triazine], simazine [2 - chloro - 4,6 - bis (ethylamino) - s-triazine], and cyanazine {2 - [ [4 - chloro - 6 - (ethylamino) -s - triazin - 2 - yl] amino] - 2 - methylpropionitrile} than Wilmington. Injury to Pensacola was noted as early as 2 weeks after the application of 2.4 kg/ha atrazine and cyanazine, whereas similar injury to Wilmington was not observed until later than 4 weeks after the treatment date. Results of 14C-atrazine treatments indicated that Wilmington bahiagrass accumulated approximately twice as much 14C-atrazine: peptide conjugate as the Pensacola cultivar.

Tillage plus trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) and prometryn [2,4-bis (isopropylamino)-6-(methylthio)-s-triazine] and tillage plus trifluralin and fluometuron [1,1-dimethyl-3-(α,α,α-trifluoro-m-tolyl)urea] applied as soil-incorporated preplanting treatments were compared with tillage alone in cotton (Gossypium hirsutum L.) grown in 51-cm and 102-cm rows on fine sandy loam soil. Over 3 yr, cotton grown in 51-cm rows yielded 15% more than cotton grown in 102-cm rows. Final cotton emergence was not altered by weed-control treatment or by planting pattern. Weed-control treatments with herbicides provided essentially complete, season-long control of grass and broadleaf weeds. At cotton layby, more weeds were in no-herbicide plots with 51-cm rows compared with 102-cm rows, but at cotton harvest numbers of weeds in both row patterns were essentially equal.

Vegetative cover of weeds was determined in 84 agricultural fields representing a number of crops in Alaska. Multivariate statistical techniques were used with weed, soil, and management data to determine if weed vegetation was related to particular environmental and management variables. Field age was the variable that best explained the variation in vegetation composition. In fields recently cleared, native species were most important, being replaced by introduced weed species with increasing field age. Field horsetail (Equisetum arvense L.) was an exceptional native species that persisted under cultivation. Total weed cover was low in the first few years of cultivation, but increased as introduced species such as common lambsquarters (Chenopodium album L.), common chickweed [Stellaria media (L.) Cyrillo], quackgrass [Agropyron repens (L.) Beauv.], and foxtail barley (Hordeum jubatum L.) became more prevalent. A number of introduced species such as hempnettle (Galeopsis tetrahit L.) and Pennsylvania smartweed (Polygonum pensylvanicum L.) were restricted to just a few fields, emphasizing the importance of using weed-free seed and other management practices to minimize the spread of introduced weeds.

Soybeans [Glycine max (L.) Merr.] were planted in an untilled, stale seedbed and conventionally tilled seedbed of Sharkey clay (Vertic Haplaquept) at Stoneville, Mississippi, in 1979 and 1980 to determine the feasibility of the stale -seedbed approach for soybean production in the Mississippi River Delta. Chemical weed control included applications of preplant, preemergence, and postemergence herbicides. Prickly sida (Sida spinosa L.) was the dominant weed in all tillage and weed-control systems. Perennial species were observed at harvest mostly in the stale - seedbed plots. Preemergence herbicides reduced the total weight of weeds per plot. Conventional seedbed preparation caused delays in planting of 3 weeks or more. In the presence of adequate soil moisture, yields of ‘Bedford,’ ‘Tracy’, and ‘Bragg’ cultivars from the stale - seedbed planting and areas that had been treated preemergence were always equal to or greater than yields from the tilled - seedbed plantings and areas that had been treated postemergence. In 1980, the hot, dry conditions of the growing season apparently negated any effect from either earlier planting or preemergence vs. post-emergence weed control.

The effects of 16 herbicides from 14 different chemical classes on levels of soluble protein, hydroxyphenolics, anthocyanin, and chlorophyll were determined in light- and dark-grown soybean [Glycine max (L.) Merr. ‘Hill’] seedlings. Growth-reducing concentrations of the herbicides were supplied to 3-day-old dark-grown soybean seedlings in liquid culture. Soluble protein (per axis) was reduced by fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone}, paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl)phenyl] methanesulfonamide}, and propanil (3′,4′-dichloropropionanilide) 24 or 48 h after treatment. In light-grown plants, soluble hydroxyphenolic compound levels were decreased on a per axis basis after 48 h by all chemical treatments except by atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], the methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate}, DSMA (disodium methanearsonate), fluridone, MH (1,2-dihydro-3,6-pyridazinedione), nitralin [4-(methylsulfonyl)-2,6-dinitro-N,N-dipropylaniline], TCA (trichloroacetic acid), and 2,4-D [(2,4-dichlorophenoxy)acetic acid]. Total chlorophyll content in hypocotyls of these seedlings was decreased by fluridone, metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5 (4H)-one], norflurazon [4-chloro-5-(methylamino)-2-(α,α,α-trifluoro-m-tolyl)-3 (2H)-pyridazinone], paraquat, and 2,4-D, but others had no significant effect. Anthocyanin accumulation in hypocotyls of 48-h light-grown seedlings was decreased by atrazine, fenuron (1,1-dimethyl-3-phenylurea), metribuzin, norflurazon, paraquat, propanil, and propham (isopropyl carbanilate). Phenylalanine ammonia-lyase (PAL) activity (previously reported work) was positively correlated with anthocyanin levels in tissues after treatment with these 16 herbicides, but not with glyphosate [N-(phosphonomethyl)glycine]. There was, however, no correlation between extractable PAL activity and chlorophyll, soluble hydroxyphenolic compounds, or soluble protein content. These results indicated that extracted PAL activities usually reflect relative in vivo activities and that PAL activity is limiting to phenylpropanoid synthesis in vivo.

Adsorption of five phenylurea herbicides, metobromuron [3-(p-bromophenyl)-1-methoxy-1-methylurea], monolinuron [3-(p-chlorophenyl)-1-methoxyl-1-methylurea], linuron [3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea], chlorbromuron [3-(4-bromo-3-chlorophenyl)-1-methoxy-1-methylurea], and CGA-15646 [3-(3-chloro-4-methylphenyl)-1,1-dimethylurea] by eight selected soils of Czechoslovakia were studied. Constants from Freundlich and Langmuir equations were calculated and correlated with the major soil properties. Freundlich K values ranged from 1.84 to 128, and the Freundlich equation was better fitted to the adsorption isotherms than was the Langmuir equation. Soil organic-matter content was the most important factor influencing the range of adsorption.

Laboratory experiments were conducted to determine the effect of moisture stress on the absorption and translocation of 14C-labeled picloram (4-amino-3,5,6-trichloropicolinic acid), dicamba (3,6-dichloro-o-anisic acid), and glyphosate [N-(phosphonomethyl)glycine] within the Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] plants. The absorption and translocation of picloram and dicamba were unaffected by moisture stress. Absorption and translocation of glyphosate to the roots and apical meristem of Canada thistle was reduced by increasing moisture stress. Weekly differential irrigation of Canada thistle field plots during the summers of 1980 and 1981 established three soil moisture regimes averaging −6.6, −11.3, and −15.0 bars at the time of herbicide treatment. When Canada thistle control was evaluated 1 year after application of glyphosate, dicamba, and picloram at 2.5, 1.1, and 0.6 kg/ha, respectively, no differences in Canada thistle shoot control were found between moisture stress treatments.

Early-preplant herbicide application for uncultivated production of soybean [Glycine max (L.) Merr. ‘Williams’] slot-seeded into untilled oat (Avena sativa L. 'Stout’) stubble was studied. Foliar- and soil-active herbicides were applied to stubble of recently harvested oats to control weeds without tillage so that soil moisture could accumulate during the fallow period. The following spring, five herbicide treatments were applied 0, 2, 4, and 6 weeks prior to soybean planting as well as preemergence to control weeds selectively in uncultivated soybeans. Broadleaf weeds were more effectively controlled than grass weeds, but both were controlled adequately with several herbicide combinations and at all five application times. Selective control of weeds was sufficient to eliminate yield loss of uncultivated soybeans seeded into untilled oat stubble. This production method could provide the Great Plains soybean producer with an effective weed control system while conserving soil, soil moisture, labor, and fuel.

Three field experiments, each for a 2-yr duration, were initiated to evaluate the efficacy of TCA (trichloroacetic acid) and dalapon (2,2 - dichloropropionic acid), alone or in combination, for the selective control of alsike clover (Trifolium hybridum L.) and red clover (T. pratense L.) during the establishment of birdsfoot trefoil (Lotus corniculatus L.). TCA at 6.7 kg/ha gave 95% control of alsike control. TCA at 13.5 kg/ha gave 92% control of red clover and the combination treatment of 6.7 kg/ha of TCA plus 9.0 kg/ha of dalapon gave 95% control of red clover. Birdsfoot trefoil tolerated TCA and dalapon alone or in combination.

Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} was aerially applied at four locations in Texas to determine effectiveness of the amine and ester formulations for the control of honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell # PRCJG]. The ester formulation was superior to the amine in most trials. Honey mesquite control with triclopyr amine was comparable to that with 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid] while control with triclopyr ester was similar to that attained with a 1:1 mixture of 2,4, 5-T and picloram (4-amino-3,5,6-trichloropicolinic acid). Honey mesquite control obtained with a 1:1 mixture of 2,4,5-T and dicamba (3,6-dichloro-o-anisic acid) was intermediate between that with the 2,4,5-T and picloram mixture and that with 2,4,5-T alone. Efficacy of triclopyr increased as rates were increased from 0.3 to 0.6 kg ae/ha and from 0.6 to 1.1 kg/ha. Triclopyr formulations were effective when applied in either water or diesel oil/water emulsions. Honey mesquite control from triclopyr in combination with picloram was generally comparable to that from the mixture of picloram and 2,4,5-T.

CGA-43089 [α-(cyanomethoximino)-benzacetonitrile] seed treatment was evaluated at three Nebraska locations during 1979 and 1980 for grain sorghum [Sorghum bicolor (L.) Moench] protection from injury by metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], four other chloroacetanilide herbicides, and three metolachlor + s-triazine combinations. Acetochlor [2-chloro-N-(ethoxymethyl)-6′-ethyl-o-acetotoluidide] caused the most frequent and severest injury to unprotected and protected sorghum. Soilincorporated metolachlor produced more consistent injury than preemergence application to unprotected sorghum, but placement did not affect CGA-43089 protection. Sorghum-stand reduction was the type of injury most frequently encountered, but crop yield was least affected. CGA-43089 always protected the grain sorghum from yield reduction with these herbicides.

Twenty-six cultivars of tomatoes from several countries were divided into four metribuzin [4-amino-6-tert-butyl-3-(methylthio)-1,2,4-triazin-5(4H)-one] tolerance groups: tolerant, semi-tolerant, semi-susceptible, and susceptible. Early maturity and tolerance to metribuzin were correlated (r = −0.78) in the field experiment and (r = −0.72) in a sinking leaf-disc bioassay. New super early cultivars were especially sensitive to metribuzin. Chlorophyll a and b content were not highly correlated with tolerance to metribuzin. Metribuzin rates used for weed control are close to toxic concentrations for very early cultivars of tomatoes. Plants in the 9-leaf stage were less sensitive than plants in the 5- or 7-leaf stage. Metribuzin tolerance came at later stages in early maturing cultivars than in later maturing cultivars.

Uptake, translocation, and metabolism of 14C-MBR-18337 {[N-[(4-ethylthio)-2-(trifluoromethyl)phenyl] methanesulfonamide]} in soybean [Glycine max (L.) Merr.] and johnsongrass [Sorghum halepense (L.) Pers.] plants and cell cultures were studied. Sixty-five percent of the 14C recovered from soybean (65% of applied) was on or in the treated leaf, compared to 81% of the 14C recovered from johnsongrass (43% of applied). Translocation of the 14C from the treated leaf of soybean was greater than from the treated johnsongrass leaf, and was primarily to the apical leaves of both species. MBR-18337, its sulfoxide, sulfone, and an unidentified polar component(s) were isolated from intact plants and cell cultures of both species. Soybean plants and cells contained greater proportions of the polar component(s) than johnsongrass plants and cells.

EPTC (S-ethyl dipropylthiocarbamate) did not reduce emergence of alfalfa (Medicago sativa L. ‘Vernal’) seedlings at 3 to 81 kg/ha in the greenhouse nor at 3 to 243 kg/ha in the field. No rate injured roots, but temporary foliar symptoms were present at all rates. Soaking seeds for 40 days in technical grade EPTC or for 8 days in water saturated with EPTC before seeding in untreated soil did not reduce emergence or injure the seedlings. Seedlings from seeds germinated in paper towels moistened with water saturated with EPTC grew normally when transferred to untreated soil. Alfalfa was injured if seedlings were exposed to EPTC after emergence, but it tolerated exposure to high concentrations during imbibition and germination of the seeds and elongation of the seedlings before they emerged from the soil. EPTC delayed seedling emergence by about 1 day. This effect was separate from that causing typical foliar symptoms.

Seedling emergence of broom snakeweed [Gutierrezia sarothrae (Pursh) Britt. & Rusby], threadleaf snakeweed [G. microcephala (DC.) Gray], common goldenweed [Isocoma coronopifolia (Gray) Greene], and false broomweed (Ericameria austrotexana M.C. Johnston) was studied in the glasshouse. Germination of these species is known to be light-stimulated. Seed of all four subshrubs germinated readily if placed on the surface or partially pressed into the soil. Emergence was reduced by covering seed with soil to a depth of less than 1 mm. Few seedlings emerged from a depth of 1 cm, and none emerged from a depth of 2 cm. Rate of emergence also decreased with increasing depth of placement. Soil texture had little effect on emergence. Rapid germination on the soil surface is consistent with other aspects of the regenerative strategy of common goldenweed and false broomweed, which do not depend upon a buried seed bank for regeneration. Seed burial probably provides a form of enforced dormancy in the small, long-lived seeds of the two snakeweed species.

C4 plants account for a small fraction of the total number of plant species (fewer than 1000 out of 250 000). A larger proportion of the world's weed species possess C4 physiology. There are 2000 species in 500 genera and 125 families of flowering plants listed in the WSSA composite list of weeds. of that number, 146 species in 53 genera and 10 families exhibit the C4 syndrome. This, as a percentage, is 17-fold greater than the percentage of C4 plants in the total world plant population. In this report, we have listed the C4 -weed species and provide specific information concerning various aspects of their Kranz anatomy and C4 physiology.

The potential interactive effects between the herbicides chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl] benzenesulfonamide}, PP009 {butyl 2-[4-[5-(trifluoromethyl-2-pyridinyl) oxy] phenoxy] propanoate}, and BAS 9052 OH {2-[1-(ethoxyimino)-butyl]-5-[2-(ethylthio)-propyl]-3-hydroxy-2-cyclohexene-one} and the air pollutant ozone (O3) on the growth of sorghum [Sorghum bicolor (L.) Moench. ‘Funk G623rg’] and velvetleaf (Abutilon theophrasti Medic. # ABUTH) were examined. All three herbicides were applied postemergence either before or after a single 6-h fumigation of sorghum and velvetleaf seedlings with O3 at 0, 0.1, and 0.2 ppmv. Chlorsulfuron was applied at 0, 0.06, or 0.12 kg ai/ha, while PP009 and BAS 9052 OH were applied at 0, 0.6, and 1.2 kg ai/ha. Two weeks after treatment, dry weight responses of velvetleaf seedlings revealed that PP009 interacted synergistically while chlorsulfuron and BAS 9052 OH interacted antagonistically with O3. The sequence of O3 fumigation and herbicide treatment appeared to be an important factor determining the type of interactive effects of these herbicides with O3. The interactive effects of all three herbicides with O3 on sorghum seedlings were additive regardless of the sequence of O3 fumigation and herbicide treatment.

Adsorption and desorption characteristics of fluridone (1-methyl-3-phenyl-5-[3-txifluoromethyl)phenyl]-4-(1H)-pyridinone} on prepared clays and organic matter were studied in unbuffered and buffered aqueous solutions. In unbuffered aqueous solution the adsorption of fluridone decreased in the order: H-saturated organic matter (H-OM) > Ca-saturated montmorillonite (Ca-mont) > Ca-saturated organic matter (Ca-OM) > kaolinite. Based on the chemistry of fluridone, the nature of the adsorbent, and previously reported studies, the major adsorption mechanisms appear to be pH-dependent adsorption of protonated fluridone and direct protonation of the herbicide at acidic surfaces, supplemented by physical adsorption forces such as van der Waals attractions and charge transfer bonds. The adsorption of fluridone on Norfolk sand (Typic Paleudult; fine-loamy, siliceous, thermic), unmodified (CK), or amended with montmorillonite (HC) or organic matter (HM) at pH 4.0, 5.2, and 7.0 was also studied. Over all adsorption was greatest on HC soil, least on CK soil, and intermediate on the HM soil. In each system adsorption was inversely related to pH. These results were interpreted by comparison with adsorption observed on prepared clay minerals and organic matter.

The effect of moderate moisture stress on the activity of the methyl ester of diclofop {2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid} applied to wild oat (Avena fatua L.) and the influence of morphological and physiological factors on the activity of the herbicide on stressed plants were investigated in growth-room experiments. Wild oat was grown in very fine sandy loam brought to a gravimetric soil moisture content (SMC) of 20% (water potential of -0.3 bars) or 10% (-6.5 bars) prior to herbicide treatment. The activity of diclofop on wild oat was slightly, but significantly, reduced when the SMC was increased from 10 to 20% immediately after spraying. Maintaining the SMC at 10% after spraying further reduced the activity of the herbicide. Wild oat plants grown at 20% SMC had 22% greater leaf area and retained 23% more herbicide than plants grown at 10% SMC. Penetration of the methyl ester of 14C-diclofop into wild oat grown at 20 or 10% SMC did not differ significantly 12, 24, or 48 h after application. Stressed and unstressed plants did not differ significantly in the metabolism of the methyl ester of 14C-diclofop. However, growth at a low SMC prior to treatment decreased the proportion of the radiolabeled herbicide recovered in the apex, third leaf, and tillers of wild oat. This may partially account for the reduced activity of this herbicide on wild oat subjected to moisture stress.