Field studies were conducted to measure the response of corn (Zea mays L. var. ‘Pioneer 3377’) to foliar applications of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid}, and haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid} as influenced by corn growth stage and the addition of 7.7, 15,4, 77.7, 140, 280, and 840 g/ai/ha of bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide]. Applications of sethoxydim (16.8, 33.6, 67.2, 100, and 134 g ai/ha), fluazifop, or haloxyfop (1.0, 2.0, 4.0, 8.0, 10.0, and 13.4 g ai/ha) to four- to five-leaf corn did not reduce seed weight, but significant reductions resulted when sethoxydim (100 g/ha) or fluazifop (13.4 g/ha) was applied to 70- to 80-cm (six-leaf) corn with or without bentazon. Corn grain yield was significantly reduced by sethoxydim (>67.2 g/ha) treatment at either growth stage of corn. In contrast, corn injury induced by fluazifop (>8.0 g/ha) and haloxyfop (13.4 g/ha) resulted in reductions in yield only when applications were made to 70- to 80-cm corn. Significant reductions in seed germination also resulted from foliar applications of the graminicides, but these reductions were inconsistent across corn growth stage.

Various populations of common lambsquarters (Chenopodium album L. # CHEAL) and late-flowering goosefoot (Chenopodium strictum Roth. # CHESG) plants were studied at the eight-to ten-leaf stage. Prior to measurement of fluorescence induction, the detached leaves were vacuum infiltrated with unformulated atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea], and pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone]. The fluorescence induction measurements were then made 1 h after adaptation in the dark. The fluorescence induction curves of intact leaves were recorded with a laboratorybuilt apparatus. A xenon lamp was used to produce the actinic beam. Cytological tests were done on meristematic cells of the root tips of the seedlings treated in 2 nM 8-hydroxyquinoline. The cytotypes were hexaploids (among which were atrazine-susceptible, pyrazon-susceptible, atrazine-resistant, and pyrazon-tolerant populations), and tetraploids (among which were atrazine-susceptible and atrazine-tolerant populations).

Three triazine-resistant biotypes of grass weeds, hood canarygrass (Phalaris paradoxa L. # PHAPA), ryegrass (Lolium rigidum Gaud.), and slender foxtail (Alopecurus myosuroides Huds. # ALOMY) were collected along roadsides on the coastal plain of Israel that had been treated repeatedly with s-triazine herbicides. Resistant biotypes (R) survived up to 4 kg ai/ha of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] applied pre-and postemergence, while susceptible (S) biotypes were killed by 0.25 kg/ha. R and S biotypes were equally sensitive to diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea]. Electron transport in chloroplasts isolated from R biotypes was not affected by atrazine, whereas in S biotypes electron transport was inhibited 50% by 0.4 to 1.0 μM atrazine. Chloroplasts from both biotypes were equally sensitive to diuron. These data indicate that the R biotypes have a plastidic mode of resistance to atrazine. In addition, seedlings of R biotypes exhibited resistance to triazinone herbicides. The R biotype of hood canarygrass was more tolerant to postemergence application of diclofop {(±)-2-[4-(2,4-dichlorophenoxy)phenoxy] propanoic acid}.

The effects of adjuvants and relative humidity (RH) on absorption, translocation, and metabolism of the methyl ester of 14C-haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid} in corn (Zea mays L. ‘B73 X Mo17’ hybrid) were evaluated. Addition of 1.0% (v/v) petroleum oil concentrate (POC) to the treatment solution resulted in greater foliar absorption and translocation of 14C than addition of 1.0% (v/v) soybean oil concentrate (SBOC), 0.1% (v/v) oxysorbic (20 POE) (polyoxyethylene sorbitan monolaurate) (OXY), or no adjuvant (NONE). The least amount of 14C absorption occurred in the treatment containing OXY. Absorption and translocation of radioactivity were significantly greater at 70% RH than at 30% RH. Thin-layer chromatography revealed that most of the 14C recovered from treated plants was in haloxyfop-methyl 5 h after treatment (HAT). The remaining 14C recovered was haloxyfop and an unidentified polar metabolite. The average percentage of 14C-haloxyfop in the nonabsorbed fraction was 5, 39, 7, and 7% for treatments containing NONE, OXY, POC, and SBOC, respectively. The ratio of haloxyfop-methyl to haloxyfop and the percentage of polar metabolite in the absorbed 14C fraction was not different among adjuvant treatments or between levels of RH.

The effects of haloxyfop {2-[4-[[3-chloro-5(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} and haloxyfop-methyl on elongation and respiration of primary roots of corn [Zea mays L. ‘B37 X Oh43’] and soybean [Glycine max (L.) Merr. ‘Hodgson 78’] were examined. Intact roots of etiolated seedlings were exposed to both forms of the herbicide. At a concentration of 10-6 M, neither form of the herbicide had an effect on elongation or respiration of soybean roots. In contrast, elongation of corn roots was completely inhibited within 24 h of exposure to 10-6 M haloxyfop. This treatment reduced the respiration rate of corn root apices by 30% but had little effect on ATP content. After 72 h of exposure to haloxyfop [10-6 M], both ATP content and respiration rate of corn root apices had declined 35%. Haloxyfop-methyl produced equivalent effects on elongation and respiration of corn roots. Studies with isolated corn root mitochondria indicated that haloxyfop inhibits electron transport at relatively high concentrations (I50 = approximately 2 mM for various substrates). Because significant reductions in ATP content and respiration rate of corn root apices were not detected during the period when elongation was inhibited (initial 24 h of exposure), it is concluded that impairment of respiration is a secondary response to the herbicide.

In controlled-environment chambers at 29/33 C day/night and 1000 μE·m-2·s-1 photosynthetic photon flux density (PPFD), increasing the CO2 concentration from 350 to 675 ppm (v/v) did not affect leaf area or total dry weight of well-watered plants of barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG], goosegrass [Eleusine indica (L.) Gaertn. # ELEIN], or southern crabgrass [Digitaria ciliaris (Retz.) Koel. # DIGSP] after 30 days. However, the whole plant transpiration rate per unit leaf area decreased, and the water use efficiency increased, in response to CO2 enrichment. In a subsequent experiment, with water availability limited by an imposed drought, CO2 enrichment reduced the effects of water stress and significantly increased leaf area and total dry weight of the three C4 grasses and soybean [Glycine max (L.) Merr. ‘Ransom’]. Growth enhancement in response to CO2 enrichment was greater in soybean than in the C4 grasses. By improving their water economy, CO2 enrichment can increase the growth of both C3 and C4 plants under water stress. However, growth stimulation can be expected to be greater in C3 plants.

Triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid), and clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were applied to honey mesquite (Prosopis glandulosa Torr. # PRCJG) on seven different dates about every 3 weeks from May to September in 1980 and 1981. Concentrations of 2,4,5-T or triclopyr in stem tissue were usually less than 2 μg/g fresh weight regardless of date of application. Concentrations of picloram and clopyralid were as high as 11 and 22 μg/g fresh weight, respectively, in upper stem phloem at some dates of application. Higher concentrations of all herbicides were detected in upper stem phloem than in the upper stem xylem or basal stem phloem or xylem. More herbicide tended to be detected in stems when herbicides were applied early (May and June) than late (August and September) in the season. Concentrations of triclopyr and picloram recovered from honey mesquite stems were about 25% greater at 3 than at 30 days after treatment, whereas concentrations of 2,4,5-T and clopyralid were about 50% greater at 3 than at 30 days after application.

Occurrence of various growth stages of major pasture plants near Lincoln, NE, were recorded for 15 yr, 1958 to 1973. The phenology of 31 perennial and 16 biennial, winter annual, and annual broadleaf species and 18 grasses was determined. Phenological stages of broadleaf species were recorded as: emergence, stem elongation, first bud, first bloom, and seed firm. Events recorded for the grasses were: emergence, culm elongation, head exserted, anthesis, and seed firm. Much variation existed in phenology among and within life habit groupings of species. Year-to-year variability in phenology of these plants was dependent on temperature patterns of specific years. Studies of this nature are useful in developing more efficient control methods for weeds, insects, and diseases.

Shoot and root growth of green foxtail [Setaria viridis (L.) Beauv. # SETVI] and yellow foxtail [Setaria lutescens (L.) Beauv. # SETLU] were compared under three moisture regimes under simulated field conditions in 1982 and 1983. An increase in water supply from 0.3 to 2.5 cm/week resulted in proportionately greater increases in the number of tillers and leaf area of green foxtail compared to yellow foxtail. In 1982, green foxtail produced approximately three times as many seed as yellow foxtail under all three water regimes, whereas under warmer conditions in 1983, green foxtail produced nearly six times as many seed as yellow foxtail under the highest water regime and more than 11 times under the lowest regime. By using a specially constructed periscope to observe root growth through clear plastic tubes implanted in the soil it was determined that the amount of available moisture had much less effect on root growth than on shoot growth of the two species. In 1982, green foxtail tended to produce more roots than yellow foxtail early in the season but as the plants matured no significant differences occurred between species. In 1983, no significant differences in total root length occurred between species at any growth stage. The roots of both species penetrated to a depth of nearly 60 cm, with the highest concentration of roots occurring at depths of 20 to 30 cm.

The relationships between microorganisms and velvetleaf (Abutilon theophrasti Medic. # ABUTH) seeds in contact with soil were studied to determine microbial effects on velvetleaf seed viability. The characteristic seed microbial association persisted on velvetleaf seeds placed on the soil surface during 32 days of incubation. The fungal association comprised of Alternaria alternata (Fr.) Keissl., Cladosporium cladosporioides (Fres.) de Vries, Epicoccum purpurascens Ehrenb. ex Schlecht, and Fusarium spp. was detected on over 50% of the seeds during incubation. Establishment of soil microorganisms on 50% of seeds occurred at only one sampling date. Such establishment was largely unsuccessful due to the effective barrier presented by seedborne microorganisms. Seedborne and soilborne microorganisms were unable to reduce viability of velvetleaf seeds in contact with soil as the total viability of all seeds tested exceeded 90% during incubation. Velvetleaf seedborne microorganisms may augment seed longevity on and in soils by acting as a barrier to potential seed decomposers originating from soil.

Research was conducted to determine percentage excretion and germination or viability of common crupina (Crupina vulgaris Cass. # CJNVU) achenes fed to sheep (Ovis aries), cattle (Bos taurus), deer (Odocoileus hemionus), horses (Equus cabullus), and Chinese pheasants (Phasianus colchicus). No achenes were found in the feces of sheep. Horses (nonruminant), deer, and cows (both ruminant animals) excreted 5, 3, and 25%, respectively, of the achenes consumed. The mean percentage achene excretion for pheasants was 23%; however, excretion was highly variable among individuals. All achenes excreted by any test species were detected within 5 days after consumption. The percentage germination or viability of excreted achenes ranged from 29% (cows) to 81% (deer). The percentage of consumed achenes that were excreted and viable ranged from 2 to 7% for large animals, whereas it was 17% for pheasants.

Plant growth, stem numbers per plant, receptacle diameters, number of Rhinocyllus conicus Froelich (Coleoptera:Curculionidae) larval cells per seed head, and mortality of the weevil within cells were monitored in infestations of the thistles Carduus thoermeri Weinmann and C. macrocephalus Deft. Both species of thistle provided similar seed head area for weevil development, and no differential effects on the biology of R. conicus were detected.

The effect of Jerusalem artichoke (Helianthus tuberosus L. # HELTU) density and duration of interference in soybeans [Glycine max (L.) Merr. ‘Hodgson 78’] was investigated in two studies. Jerusalem artichoke densities of 1, 2, and 4 tubers/m of row reduced soybean seed yield by 31, 59, and 71%, respectively. Soybean height, branches/plant, pods/plant, and seed weight were usually reduced by all three weed densities. Soybean leaf area and relative growth rates were reduced by densities of 2 and 4 tubers/m of crop row, and net assimilation rate (NAR) was reduced by 4 tubers/m of crop row. Jerusalem artichoke interference at 4 tubers/m of row for 4, 6, 8, and 20 weeks (full season) reduced soybean yields 9, 10, 38, and 82%, respectively. Branches/plant, pods/plant, and seeds/plant were reduced after 8 weeks of interference. These results suggest that Jerusalem artichoke is highly competitive with soybean and should be controlled within 6 weeks after planting.

An experiment was conducted at five locations in Nebraska to determine the extent of demise of weed seed in soil when seed production was eliminated from 1975 through 1979 in corn (Zea mays L.). Weed yields, weed seed production, and corn yields were determined under four weed management levels in 1980. Annual broadleaf weed seed were more prevalent than grass seed in cultivated soil throughout the study. The population of viable weed seed in soil declined 95% during the 5-yr period that weed seed production was eliminated. Weed seed buildup recovered to within 90% of the 1975 level during 1980 at Concord and Clay Center but remained low at Lincoln, North Platte, and Scottsbluff. Thus, seed longevity in soil was sometimes sufficient to withstand modern weed control methods and still reinfest a field after 5 yr of eliminating weed seed production. Corn yields were maintained 1 yr with minimum weed management effort following 5 yr of no weed seed production.

Perennial pepperweed (Lepidium latifolium L. # LEPLA) is a serious weed of meadows and riparian habitats in the intermountain area of the western United States. Germination of seeds of this species was tested at 55 constant- and alternating-temperature regimes. No significant differences were found in mean germination at a range of temperatures varying from 0 to 40 C for seedlots collected at the same site in different years or at different locations in the same year. Optimum germination not significantly (P = 0.01) lower than the maximum observed occurred most frequently at 5/40 C (5 C for 16 h and 40 C for 8 h), and 10/40 and 15/40 C. Germination was enhanced by alternating regimes with low night temperatures (0, 2, or 5 C) and high day temperatures (35 and 40 C), in comparison with more moderate constant-temperature regimes.

The potential of preventing seed production and reducing seed viability of weeds that commonly grow taller than soybeans [Glycine max (L.) Merr. ‘Williams 82’] was evaluated. Chlorflurenol (2-chloro-9-hydroxy-9H-fluorene-9-carboxylic acid), chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide}, and glyphosate [N-(phosphonomethyl)glycine] were evaluated against sparse stands of velvetleaf (Abutilon theophrasti Medik. # ABUTH) and giant foxtail (Setaria faberi Herrm. # SETFA) growing in soybeans. Simulated-roller applications of all three herbicides significantly reduced seed production and germination of both weeds, although glyphosate was more effective than were the other two. Applications during early flowering of velvetleaf and early heading of giant foxtail reduced seed production more than later applications when some seeds were present. With the early application of glyphosate, 99% prevention of velvetleaf and 96% prevention of giant foxtail seed production were attained. With the early glyphosate application, germination of seeds produced was reduced by 50% in velvetleaf and by 95% in giant foxtail. Soybean yields were not reduced by either glyphosate or chlorflurenol but were drastically reduced by chlorsulfuron.

Seed dormancy and soil longevity characteristics of three weedy cowpea [Vigna unguiculata (L.) Walp.] cultivars were investigated. Seed germination was maximum at 40 C; however, ‘Clay’ had greater germination than ‘Black’ or ‘Red Ripper’ cowpea at temperatures ≥ 20 C. Concentrated sulfuric acid soaks, hot (70 C)-water soaks, and piercing the seed coat promoted germination. Seed with an initial water content of 12.3% were stored at relative humidities ranging from 0 to 60% at 25 C. After 4 weeks of storage at relative humidities of 0 to 50%, seed water content varied from 4.6 to 11.4%. Germination and hard seed content was 11% or more and 89% or less, respectively, for seed with water content ranging from 6.9 to 11.4%. Except for seed with an initial water content of 6.9%, cowpea seed water content increased after 3 weeks of storage in a 70% relative humidity environment. Rehydration increased germination for seed with initial water content of 9.2% or more, but not for seed with initial water content of 8.4% or less. In mid-November 1981 and 1982, Black, Clay, Red Ripper, and sicklepod (Cassia obtusifolia L. # CASOB) seed were buried at soil depths of 2.5, 7.5, and 15 cm for 3, 6, and 9 months. Seed survival of Black and Red Ripper was similar to that of sicklepod; however, longevity of Clay seed was less than sicklepod. Survival was greater for seed buried in 1981 than in 1982 because of low seed water content of the 1981 seedlots.

White horehound (Marrubium vulgare L. # MAQVU) is one of the few perennial, herbaceous alien weeds to successfully colonize semiarid to arid rangelands in the Great Basin. Seeds of white horehound, collected from diverse habitats within the Lahontan Basin of northwestern Nevada, were incubated at constant or alternating temperatures ranging from 0 to 40 C. Germination was low and largely limited to alternating temperatures (10 to 25 C alternating with 35 to 40 C). At least a 15-C range in diurnal fluctuation was required for optimum germination (defined as not lower than the maximum observed minus one-half of the confidence interval with 1% probability). Cool-moist stratification at 2 C for 4 to 8 weeks enhanced germination at optimum temperature regimes by as much as 70% and increased overall average germination by 35 to 40%. Cool-moist stratification caused a shift in temperature optima for germination from widely fluctuating temperatures to constant 15 or 20 C. The magnitude of this shift varied among sources of seeds.

The growth and development of field horsetail (Equisetum arvense L. # EQUAR) was measured outdoors using potted plants grown from one-node rhizome fragments. Shoot growth rate increased slowly after planting in March, accelerating to a maximum during July with maximas for shoot height during August and shoot number in September. Rhizome system growth rates initially followed a similar pattern to that of the shoots achieving a maximum during July. Dry matter accumulated in the rhizomes until October and declined thereafter throughout the winter. Tubers initiated during August grew in size and number until November, well beyond the period of active shoot growth and onset of senescence. The characteristics of the growth and development of field horsetail are discussed in relation to achieving weed control via cultural and herbicide treatments.

Ground applications of pelleted tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} at 0.6 kg ai/ha (20% formulation) reduced big sagebrush (Artemisia tridentata Nutt. # ARTTR) density by an average of 84 and 92% after 28 months, whereas 1.1 kg/ha killed 94 and 97% of the plants when applied in January or May, respectively. Total standing crop of grasses was unaffected 4 months after tebuthiuron applications. Significant increases in grass production occurred during the second and third growing seasons following tebuthiuron treatment. Desirable forage grasses such as galleta [Hilaria jamesii (Torr.) Benth.], blue grama [Bouteloua gracilis (Wild. ex H.B.K.) Lag. ex Griffiths], and crested wheatgrass [Agropyron cristatum (L.) Gaertn.] generally increased in tebuthiuron-treated plots, whereas sand dropseed [Sporobolus cryptandrus (Torr.) Gray # SPECR] and ring muhly [Mulenbergia torreyii (Kunth.) Hitchc. & Chase] production remained unchanged in comparison with untreated areas.