bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Horsenettle (Solanum carolinense) on Snapbean (Phaseolus vulgaris)
Authors: Frank J. Ray
Published: May 2019

Field experiments were conducted in 1987 and 1988 at Frederick, MD, to determine established horsenettle (Solanum carolinenseL.) interference with snapbean. Horsenettle grown for 3 yr prior to planting snapbeans reduced yield 65% in 1987 and 48% in 1988. Horsenettle established for 1 yr reduced snapbean yield 20 and 18% in 1987 and 1988, respectively. As the distance of the snapbean row from the horsenettle row increased, there was less effect on the yield of snapbean. In 1987, snapbean yield in rows 15, 30, or 60 cm from horsenettle was reduced 43, 29, and 15%, respectively, while during 1988 in the same plots snapbean yields were reduced 38, 26, and 11%. Eight horsenettle planted in a 4.6-m row the first year and 16 horsenettle per row for the second year reduced snapbean yield 36 and 55% respectively. Horsenettle fruit number was 16% lower the first year and 45% lower the second year when snapbeans were grown at a 15-cm row spacing instead of a 60-cm row spacing.
Downy Brome (Bromus tectorum) Interference and Economic Thresholds in Winter Wheat (Triticum aestivum)
Authors: Stahlman Phillip W. , Miller Stephen D.
Published: May 2019

Densities up to 100 downy brome m2were established in winter wheat in southeastern Wyoming and west-central Kansas to quantify wheat yield loss from downy brome interference and to approximate economic threshold levels. A quadratic equation best described wheat yield loss as a function of weed density when downy brome emerged within 14 days after wheat emergence. Densities of 24, 40, and 65 downy brome m2reduced wheat yield by 10, 15, and 20%, respectively. Wheat yield was not reduced when downy brome emerged 21 or more days later than wheat. Economic thresholds varied with changes in downy brome density, cost of control, wheat price, and potential wheat yield. In a greenhouse experiment, dry weight of 72-day-old wheat plants grown in association with downy brome was not affected by the distance between the weeds and wheat, whereas downy brome plant dry weight increased with increasing distance between the weeds and wheat.
Influence of Sulfonylurea and Other Herbicides on Selected Woody and Herbaceous Species
Authors: Meyer Robert E. , Bovey Rodney W.
Published: May 2019

Chlorsulfuron and metsulfuron were effective on Texas whitebrush, killing 70 to 75% of the plants at 0.28 kg ai ha, marginally effective on Macartney rose, killing 15 to 43% of the plants at 1.12 kg ha, but ineffective on honey mesquite and huisache, killing no more than 10% of the plants at 1.12 kg ha. Sulfometuron was ineffective on all woody species at 1.12 kg ai ha. Clopyralid and picloram were effective, killing 70 to 92% of the huisache at 2.24 kg ae ha. Tebuthiuron killed 72% of the Texas whitebrush at 1.12 kg ai ha. Sulfometuron generally reduced herbaceous plant cover the year of application. Chlorsulfuron and metsulfuron often resulted in increased grass cover the year of application. Most herbicides reduced broadleaf weeds the year of application. Woolly croton often was the first prominent broadleaf species to return to areas treated with clopyralid and sulfometuron. Few differences occurred among herbicides in herbaceous weed cover the year following treatment.
Sorption of Organic Compounds by Plant Cuticles
Authors: Bukovac Martin J. , Petracek Peter D. , Fader Royal G. , Morse Ronald D.
Published: May 2019

Relevant data on the sorption of organic compounds by isolated plant cuticles are reviewed and discussed in relation to the foliar penetration process. The chemical properties and structure of plant cuticles favor sorption of lipophilic compounds and play an important role in the penetration of biologically active substances. With organic acid auxins 2,4-D and NAA, and methylene blue as molecular probes, concentration, pH, temperature, and surfactants were important factors affecting sorption. The constituent waxes of the cuticle markedly inhibit sorption of a wide range of organic compounds. Octoxynol surfactants that have 5 or 7.5 polyoxyethylene groups interact with the epicuticular wax to enhance the sorption of NAA. At sorption equilibrium, the cuticle has a lower affinity for methylene blue in the region usually rich in cuticular waxes and in a narrow band in the cuticular pegs.
Phloem Mobility of Xenobiotics. III. Sensitivity of Unified Model to Plant Parameters and Application to Patented Chemical Hybridizing Agents
Authors: Hsu Francis C. , Kleier Daniel A.
Published: May 2019

A refined model for the phloem translocation of xenobiotics in living plants is presented. The model accounts for the translocation of a xenobiotic that can exist in several ionic forms in terms of the permeabilities of these forms and the fractions of the forms that exist both within the sieve tubes and in the surrounding apoplast. Predictions of the model are quite sensitive to the description of the membranes used in the model, with optimum log Kow's and pKa's becoming more positive as the membranes become less permeable. The literature generally supports the predictions of the model. When applied to patented chemical hybridizing agents, the model predicts that most are phloem-mobile. This prediction strongly suggests that the chemical hybridizing agents exert their pollen-suppressing activity by direct effects on pollen and/or the surrounding maternal tissues. With low transpiration rates and the discontinuity of xylem in many reproductive tissues, phloem translocatability may be an essential requirement for the whole plant activity of many chemical hybridizing agents.
Self-Limitation of Herbicide Mobility by Phytotoxic Action
Authors: Geiger Donald R. , Bestman Hank D.
Published: May 2019

Translocation of phloem-mobile herbicides was inhibited by their phytotoxic action on processes that maintain assimilate translocation. Glyphosate lowered import into developing sink leaves soon after it was applied to exporting sugarbeet leaves. Later, photosynthesis slowed down and starch accumulation stopped, but export of both assimilate and glyphosate continued until it was limited by starch availability at night Experiments with field pennycress and Tartary buckwheat indicated that self-limitation of chlorsulfuron translocation probably occurred and that it resulted from lowered assimilate entry into phloem rather than from inhibition of photosynthesis or carbon allocation. Leakage of chlorsulfuron from the phloem when export was slowed down also may have contributed to its reduced translocation.
Oxadiazon Activity is Similar to That ofp-Nitro-Diphenyl Ether Herbicides
Authors: Duke Stephen O. , Lydon John , Paul Rex N.
Published: May 2019

Oxadiazon (10 μM) caused rapid, light-dependent membrane damage to cucumber cotyledon discs. Electrolyte leakage was detected within 1 h of exposure to light, as were cytoplasmic vesiculation and breakage of the tonoplast and plasmalemma. The ultrastructure of chloroplasts was not affected until the cytoplasm was dispersed. Photosynthetic inhibitors had no effect on activity and, after a period of dark incubation with oxadiazon, there was little effect of temperature on the light-caused membrane destruction. Porphyrin synthesis inhibitors (gabaculine and 4,6-dioxoheptanoic acid) almost completely prevented the herbicidal activity of oxadiazon. Oxadiazon treatment caused accumulation of protoporphyrin IX, a photodynamic pigment. Oxadiazon caused physiological effects on cucumber cotyledons that were virtually identical to those ofp-nitro-diphenyl ether herbicides like acifluorfen and its methyl ester, which have recently been shown to also cause protoporphyrin IX accumulation.
Bristly Starbur (Acanthospermum hispidum) Interference in Peanuts (Arachis hypogaea)
Authors: Walker Robert H. , Wells Larry W. , McGuire John A.
Published: May 2019

The effects of bristly starbur interference with peanuts were studied from 1980 through 1983 on a Dothan sandy loam (Plinthic Paleudults). Peanut seed yields, which included kernels plus hulls, were reduced as bristly starbur densities increased from 2 to 64 plants/7.5 m of row. Full-season interference from 8, 16, 32, and 64 bristly starbur plants/7.5 m of row reduced peanut seed yields 14, 26, 43, and 50%, respectively. The seed yield of peanuts maintained weed free for 6 weeks after crop emergence was reduced by no more than 3% compared to peanuts maintained weed free for the entire season. Weed interference for 2 weeks after crop emergence reduced seed yield by an average of 4% over the 3-yr period, based on prediction equations. Bristly starbur interference for 13 weeks after crop emergence reduced peanut forage dry weight yield by 54%. Similarly, peanut interference for 13 weeks after emergence reduced bristly starbur forage dry weight yield by 32%. Bristly starbur density in the forage dry weight studies averaged 35/7.5 m of row. These bristly starbur were confined to a 35-cm band over the drill. Peanut density averaged 72/7.5 m of drill.
Growth and Development of Florida Beggarweed (Desmodium tortuosum) Selections
Authors: Cardina John , Brecke Barry J.
Published: May 2019

Florida beggarweed seeds were collected in Georgia, Florida, and South Carolina from plants differing in morphological characteristics. Seedlings were transplanted into peanut rows in field studies at Tifton, GA, and Jay, FL, in 1986 and 1987, and frequent observations of vegetative and reproductive characteristics were made. The competitiveness of the Florida beggarweed selections was evaluated by comparing pod weights from peanut plants grown in rows adjacent to the individual weed selections with pod weights of weed-free peanuts. There were significant differences among selections of Florida beggarweed in days to maximum height, maximum node formation, maximum branching, and initial flowering and fruiting at both locations. Selection GA-1 generally reached these growth stages earliest, was shorter, narrower, had fewer nodes, and produced less dry matter and fewer seeds than GA-2, which was generally the latest maturing selection. GA-4 produced fewer branches and smaller seeds than the other selections. Peanut pod weights adjacent to Florida beggarweed plants were reduced 12 to 18% in 1986 and 10 to 24% in 1987 compared to weed-free checks. Florida beggarweed selection GA-2 was the most competitive and GA-4 was among the least competitive both years. The variation of measured parameters among Florida beggarweed selections in this study may contribute to the survival and adaptability of this weed with changing environmental conditions, cultural practices, and control measures.
The Influence of Herbicide Formulation on Weed Control in Four Tillage Systems
Authors: Johnson Michael D. , Wyse Donald L. , Lueschen William E.
Published: May 2019

The objectives of this research were to compare the weed control efficacy of liquid, granular, and microencapsulated formulations of preemergence herbicides in moldboard plow, chisel plow, ridge tillage, and no-tillage corn and soybean production systems, and to determine whether herbicide formulation can influence herbicide interception and retention on surface corn residue. Common lambsquarters populations were threefold higher in corn than in soybeans. A mixed population of giant foxtail and green foxtail was highest in the chisel plow and lowest in the ridge tillage system as were total weed numbers. Percent weed control was not influenced by tillage when considered across all herbicide treatments. Weed control was not influenced by herbicide formulation in the moldboard plow, chisel plow, or ridge tillage systems, but granular herbicide applications provided better weed control than liquid applications in the no-tillage system and across various rates of corn residue in an experiment with no tillage variables. Two- to threefold less granular-applied herbicide was intercepted by surface corn residue at the time of application compared to liquid-applied herbicide. Increasing amounts of postapplication rainfall decreased the difference among formulations with regard to both total soil reception of the herbicide and resultant weed control. There was no consistent advantage for the microencapsulated formulation over the other herbicide formulations. Surface corn residue controlled many weeds without the aid of a herbicide and actually contributed to overall weed control even where herbicides were applied. This suggests that the binding of preemergence herbicides on surface crop residue may not be the cause of weed control failures in reduced-tillage systems as is often assumed to be the case.
Tolerance of Tomato (Lycopersicon esculentum) and Bell Pepper (Capsicum annum) to Clomazone
Authors: Weston Leslie A. , Barrett Michael
Published: May 2019

Pronounced differences in the tolerance of tomatoes and bell peppers to clomazone observed in field studies were confirmed in a greenhouse experiment. In greenhouse studies, preemergence clomazone rates causing 50% visible injury on bell pepper and tomato seedlings 10 days after application were 9.4 and 0.1 kg/ha, respectively. Based on growth inhibition, bell peppers were 40-fold more tolerant of clomazone than tomatoes 20 days after clomazone application. In laboratory studies investigating the basis for differential clomazone tolerance, no differences in uptake of 14C-clomazone from nutrient solutions between tomato and bell pepper plants were observed after 24 h. Minor differences were observed in the distribution of 14C label within plants; a higher percentage of 14C was recovered in bell pepper roots than in tomato roots, while the opposite was true for the shoots. Clomazone was metabolized to two products in roots of both bell peppers and tomatoes within 48 h after treatment. Tomato shoots were more active in converting clomazone to these metabolites than were tomato roots. Bell pepper roots converted more clomazone to metabolites than did tomato roots 24 h after treatment. However, by 72 h, differences in clomazone metabolite levels between species were negligible in both roots and shoots. Enzymatic and acid hydrolysis of soluble, polaf clomazone metabolites indicated that these metabolites may be sugar conjugates of clomazone.
Qualitative and Quantitative Characterization of Phenolic Compounds from Lantana (Lantana camara) Leaves
Authors: Jain Rakesh , Singh Megh , Dezman David J.
Published: May 2019

Phytotoxins from lantana leaves were extracted in aqueous media adjusted to pH 4, 7, or 10. All three leaf extracts showed considerable phytotoxic activity in duckweed growth bioassay. The acidic and the neutral extracts of lantana leaves at 10 g fresh weight/L were more phytotoxic to duckweed growth than the alkaline extract at the same concentration. Phenolic compounds present in lantana leaves were isolated by alkaline hydrolysis of the crude leaf extracts followed by separation of the various components in ether or aqueous media. The fraction containing the phenolics showed considerable phytotoxic activity against duckweed growth. In addition, the fraction containing the nonpolar substances separated from the acidic and the neutral crude extracts also showed significant phytotoxic activity against duckweed growth. No attempt was made to isolate and identify the phytotoxic component from the nonpolar fraction. Characterization of the phenolic fraction by HPLC revealed the presence of at least 14 phenolic compounds. All three leaf extracts contained the same array of phenolic compounds. However, the quantity of phenolic compounds extracted varied with the pH of the extraction medium. The acidic extract containedp-hydroxybenzoic acid (0.09 mM) as the most abundant phenolic compound, whereas the neutral and the basic extracts containedp-coumaric acid (0.11 and 0.26 mM, respectively) as the most abundant phenolic compound. All phenolic compounds, exceptp-hydroxybenzoic acid, proved phytotoxic to duckweed growth at a concentration of 1 mM or lower. Salicylic acid was the most phytotoxic of the phenolic compounds detected in lantana leaf extracts. The phytotoxicity of lantana leaf extracts is probably partly due to a complex interaction of all phenolic compounds present.
Italian Ryegrass (Lolium multiflorum) Accessions Tolerant to Diclofop
Authors: Stanger Charles E. , Appleby Arnold P.
Published: May 2019

In 1987, two applications of the methyl ester of diclofop failed to effectively control Italian ryegrass in some growers' fields. As a result of these observations, studies were initiated to determine if the surviving ryegrass is more tolerant to diclofop than previously untreated ryegrass. Growth chamber studies on five accessions of ryegrass demonstrated that collections from two growers' fields were highly tolerant of diclofop. Diclofop GR50(rate required to reduce shoot weight by 50%) values of accessions A and B and commercial ryegrass, when diclofop was applied to seedlings at the two-leaf stage, were 2.9, 3.4, and 0.0056 kg ai/ha, respectively. Diclofop-tolerant biotypes were not more tolerant to postemergence barban or preemergence-incorporated triallate plus postemergence diuron or metribuzin. These herbicides are possible alternative treatments in fields where diclofop is no longer effective.
The Involvement of Cork-Silica Cell Pairs in the Production of Wax Filaments in Johnsongrass (Sorghum halepense) Leaves
Authors: McWhorter Chester G. , Paul Rex N.
Published: May 2019

Wax filaments > 100 μm long on the epidermis of johnsongrass leaves and culms occurred only around the edge of costal cork-silica cell pairs and intercostal silica cells. Silica cells alternating with cork cells occurred in rows over veins. Solitary or occasionally paired cork-silica cells occurred between veins. The high silicon content of silica cells was verified with X-ray mapping of silicon. X-ray analysis also indicated that wax filaments contained silicon. Scanning electron micrographs (SEM) of dislodged intercostal silica cells showed that wax filaments emerged from an integument that surrounded the silica cell. It is theorized that at high ambient temperatures the silica gel in silica cells provides the localized cooling necessary to solidify liquid wax constituents as they are extruded onto the surface of the plant.
Interaction Between a Velvetleaf Isolate ofColletotrichum coccodesand Thidiazuron for Velvetleaf (Abutilon theophrasti) Control in the Field
Authors: Wymore L. A. , Watson A. K.
Published: May 2019

Spraying with tank mix combinations of the fungusColletotrichum coccodesand the plant growth regulator thidiazuron increased mortality, decreased biomass and height of velvetleaf, and increased soybean yield in field experiments. The velvetleaf isolate ofC. coccodeswas compatible with thidiazuron, and tank mix combinations consistently improved control over either component alone. In the moist 1986 season the fungus and the growth regulator interacted synergistically to increase velvetleaf mortality. In the drier 1987 season no significant interaction was detected between the two components.
Histological and Cytological Effects of Haloxyfop on Sorghum (Sorghum bicolor) and Unicorn-Plant (Proboscidea louisianica) Root Meristems
Authors: Vaughn Steven F. , Merkle Morris G.
Published: May 2019

The effects of haloxyfop on elongation, mitotic index, and morphology of sorghum and unicorn-plant primary roots were examined. Elongation of sorghum roots was completely inhibited by haloxyfop concentrations of 10–6M or greater 24 h after treatment, whereas unicorn-plant root elongation was unaffected by the same concentrations 72 h after treatment. Mitotic indices of sorghum roots were reduced by both 10–6and 10–8M haloxyfop, with the higher concentration reducing the index to near zero by 24 h of exposure. The mitotic indices of unicorn-plant roots were unaffected by the same levels of the herbicide after both 24- and 48-h treatment. Histological analyses showed that after 24 h exposure to 10–6M haloxyfop, large vacuoles were present in cells at the root apex that normally did not exhibit these organelles. After 48 h of exposure many cells in the apical region appeared to lack visible cytoplasm and/or nuclei, and by 72 h only cell walls remained visibly evident, and many cells had collapsed. These changes are similar to those that occur in tissues undergoing senescence. Treatment of sorghum roots with 10–8M haloxyfop did not cause discernible changes after 72 h. Unicorn-plant roots treated with 10–6M haloxyfop appeared unaffected after 72 h.
Effect of Sethoxydim and Haloxyfop on Acetyl-Coenzyme a Carboxylase Activity inFestucaSpecies
Authors: Stoltenberg David E. , Gronwald John W. , Wyse Donald L. , Burton James D. , Somers David A. , Gengenbach Burle G.
Published: May 2019

In greenhouse studies, the calculated I50(herbicide application resulting in 50% inhibition of shoot regrowth) in tall fescue was approximately 0.004 kg/ha for both sethoxydim and haloxyfop. In red fescue, the I50for sethoxydim and haloxyfop was 9.4 kg/ha and 0.04 kg/ha, respectively. As measured in crude cell extracts of tall fescue, incorporation of14C-acetyl-coenzyme A into fatty acids was inhibited 62 and 71% by 10 μM sethoxydim and 10 μM haloxyfop, respectively. In red fescue, 10 μM haloxyfop inhibited14C-acetyl-CoA incorporation into fatty acids by 29%, whereas 10 μM sethoxydim had no effect. The I50for inhibition of acetyl-coenzyme A carboxylase activity in tall fescue with sethoxydim and haloxyfop was 6.9 and 5.8 μM, respectively. In red fescue the I50for haloxyfop was 118 μM. Sethoxydim concentrations as high as 1 mM had little effect on acetyl-coenzyme A carboxylase activity in red fescue. These results suggest that acetyl-coenzyme A carboxylase is a sensitive site of action for sethoxydim and haloxyfop in tall fescue, and that tolerance to these herbicides in red fescue is due to the presence of a more tolerant form of the enzyme.
Influence of Planting Date on Growth of Bermudagrass (Cynodon dactylon)
Authors: Keeley Paul E. , Thullen Robert J.
Published: May 2019

Bermudagrass plugs were transplanted from the greenhouse to the field at monthly intervals from March through October at Shafter, CA. Emergence began from the March plantings when soil temperatures at a depth of 5 cm reached 17 C. Although the initial growth of March, April, and May plantings was very slow, these plantings eventually produced about 60% more dry matter (2100 g/m2) than June, July, and August plantings (1300 g/m2) when harvested in December. At 8 weeks after planting, June to August plantings accumulated 120% more dry matter (460 g/m2) than March to May plantings (210 g/m2). At 12 weeks, dry matter accumulation was greatly reduced by shorter photoperiods and cool temperatures for March and September plantings (160 g/m2) when compared to all intermediate plantings (700 g/m2). All plantings, except October, produced rhizomes (15 to 120/m2) and seeds (154 to 73400/m2) before killing frosts occurred in late November. Although rhizomes and seeds were not collected until the 12-week harvest for the March to May plantings, these plantings produced or tended to produce the greatest number of rhizomes (85/m2) and seeds (49300/m2) by December. Rhizomes and seeds from the June to September plantings were collected within 8 weeks, indicating that declining photoperiods hastened rhizome and seed production.
Response of Gas Exchange in Jointed Goatgrass (Aegilops cylindrica) to Environmental Conditions
Authors: Gealy David R.
Published: May 2019

Gas exchange of jointed goatgrass leaves was affected by temperature, irradiance level, and soil matric potential. Net photosynthesis of leaves under saturating irradiance (PPFD3= 1850 (μE·m–2·s−1) was optimum at about 20 C. At 25 C, net photosynthesis was nearly 90% of maximum at a PPFD of 800 μE·m–2·−1. Transpiration, and presumably water use, increased steadily with temperature from 10 to 40 C. Dark respiration rate and compensation points for light and for CO2increased exponentially, or nearly so, from 10 to 40 C. Soil moisture deficits of −130 kPa reduced net photosynthesis and transpiration by about 30 and 55%, respectively, compared to well-watered plants.
Effects of Tillage on Trifluralin Residue Carryover Injury to Corn (Zea mays)
Authors: Hartzler Robert G. , Fawcett Richard S. , Owen Michael D. K.
Published: May 2019

Trifluralin was evaluated at 1.1, 2.2, and 4.5 kg/ha in 1983 and 1984 at two locations in Iowa for residue carryover injury to corn the following seasons. Three methods of seedbed preparation (no-till, moldboard, and chisel plowing) for corn planting were also examined. There was no effect on corn growth at the 1.1 kg/ha rate of trifluralin. Averaged over the four experiments, reductions in corn height of 8 and 24% were observed 5 weeks after planting at 2.2 and 4.5 kg/ha, respectively. The relative degree of stunting due to trifluralin decreased as the growing season progressed. Early-season carryover injury was more severe in reduced tillage than in moldboard plow treatments in the 1983-84 Nashua experiment. Moldboard and chisel plowing reduced the concentration of trifluralin in the 0- to 7.5-cm zone of the soil profile by 62 and 31%, respectively, when compared to no-till. No yield reductions were observed at the 1.1 or 2.2 kg/ha rate of trifluralin. In 1984, grain yields were reduced by 8 and 16% at Ames and Nashua, respectively, by the 4.5 kg/ha trifluralin rate.
Tolerance of Corn (Zea mays) Lines to Clomazone
Authors: Keifer David W.
Published: May 2019

Corn hybrids and inbreds were ranked for their relative tolerance to soil-incorporated clomazone, as assessed by the level of discoloration injury in the greenhouse. Inbred W117 was the most tolerant corn line tested. Some corn lines were affected similarly by clomazone. Inbred A619 was in the most susceptible group. Clomazone injury to A619 (susceptible) and W117 (tolerant) corn was similar when the clomazone rate was 10-fold greater on W117 than on A619. The distribution of corn lines on a sensitivity scale was of limited range; the distribution of hybrids on this scale was a single symmetrical peak. Changing the growth temperature or soil composition would change the absolute level of corn injury caused by a rate of clomazone but did not change the relative ranking of the corn lines in the test. A subset of the greenhouse-tested corn lines also was evaluated in several field locations. The tolerance of corn in a given field was highly (P<0.005) correlated with tolerance in the greenhouse; however, the absolute levels of injury differed among locations. The tolerance of- hybrids of known pedigree was highly (P<0.0002) correlated with the tolerance of the parent inbreds, indicating this trait was inherited.
Behavior of Imazethapyr in Soybeans (Glycine max), Peanuts (Arachis hypogaea), and Selected Weeds
Authors: Cole Tracy A. , Wehtje Glenn R. , Wilcut John W. , Hicks T. Vint
Published: May 2019

Imazethapyr was applied at 0.14 kg ae/ha to soybean, peanut, sicklepod. Florida beggarweed, and redroot pigweed as either a soil, foliar, or soil plus foliar application. Soybean and peanut were the most tolerant species; redroot pigweed was the most sensitive, with sicklepod and Florida beggarweed being intermediate. Foliar or foliar plus soil applications were more effective in reducing sicklepod and Florida beggarweed fresh weights than soil application alone. Foliar absorption of14C-imazethapyr 72 h after treatment was greater than 90% for soybean, peanut, sicklepod, and redroot pigweed, but only 77% in Florida beggarweed. For the species evaluated, the amount translocated from the treated leaf ranged from 5 to 16% after 72 h. Within this same time period, an average of 90% of the root-absorbed imazethapyr had been translocated to the shoot in all species except peanut. The half-life of imazethapyr was 6.6, 6.5, 14.4, 24.0, and 32.1 days in soybean, peanut, Florida beggarweed, sicklepod, and redroot pigweed, respectively. Tolerance was most closely associated with imazethapyr half-life within these species.
The Potential Allelopathic Characteristics of Bitter Sneezeweed (Helenium amarum)
Authors: Smith Albert E.
Published: May 2019

Research was conducted to determine the potential for allelopathy to occur in pastures infested with bitter sneezeweed. Aqueous extracts of bitter sneezeweed leaves reduced alfalfa and Italian ryegrass seedling growth as much as 50% at concentrations of 0.5% (w/v). Leaf extracts were more phytotoxic than either stem or root extracts and seedling growth was reduced more than seed germination. Bitter sneezeweed tissue mixed in potting soil at concentrations as low as 0.3% w/w reduced alfalfa seedling numbers by 43%, plant height by 26%, and foliage dry matter production by 54% compared to plants cultured in soil without bitter sneezeweed leaf tissue. The potential concentration of bitter sneezeweed leaf material in soil in the pasture ecosystem was determined to be 0.5% w/v in the liquid phase and 0.2% w/w in the solid phase. Alfalfa seedling growth was reduced by 70% when germinating seed were placed under a bell jar with a potted mature bitter sneezeweed plant compared to control seedlings. A potential exists for bitter sneezeweed interference with developing alfalfa and Italian ryegrass seedlings following fall interseeding into pastures infested with bitter sneezeweed.
Sicklepod (Cassia obtusifolia) Control in Soybean (Glycine max) Grown in Rotations of 97- and 18-cm Row Spacings
Authors: Shaw David R. , Smith Clyde A. , Snipes Charles E.
Published: May 2019

Various 3-yr rotation sequences of 97- and 18-cm row spacings, with appropriate sicklepod control treatments within each row spacing, were implemented to evaluate sicklepod population and soybean yield at two locations. Alachlor plus metribuzin applied preemergence followed by either a postemergence-directed spray of metribuzin plus 2,4-DB or hand hoeing in 97-cm rows consistently reduced sicklepod populations. Reductions with 97-cm rows and preemergence-applied herbicides coupled with cultivation were not as great. At one location, using a split application of metribuzin preplant incorporated followed by preemergence with 18-cm rows reduced sicklepod populations if effective control measures had been used in wide rows the previous year, but the narrow-row treatments did not reduce sicklepod numbers if 18-cm rows had been used previously. Soil-applied metribuzin was more effective under high soil pH conditions, and sicklepod populations were reduced substantially whether the previous row spacing was 18 or 97 cm. After the third year, all plots were planted in 97-cm rows with no herbicides. No differences were found among sicklepod populations with any previous row spacing or sicklepod control program, indicating that, even with 3 yr of effective control, subsequent sicklepod populations were not affected.
Interference Between Soybeans (Glycine max) and Common Cocklebur (Xanthium strumarium) Under Indiana Field Conditions
Authors: Henry William T. , Bauman Thomas T.
Published: May 2019

The effects of interference between soybeans and common cocklebur were investigated. Common cocklebur interference reduced soybean growth at each of four sample dates during the growing season. The area of interference surrounding individual common cocklebur plants within the soybean row fluctuated over time with respect to intensity and spatial distribution. Soybean growth was significantly reduced up to 10 cm away from individual cocklebur plants at 6 weeks after planting (WAP), 30 cm at 8 WAP, 20 to 30 cm at 10 WAP, and 40 cm at 12 WAP. The maximum possible distance of cocklebur influence, determined by regression analysis, also varied during the growing season. When areas of interference from adjacent cocklebur plants overlapped, the cumulative influence was found to be additive, especially late in the growing season. Soybean interference caused a 50 to 90% reduction in the size of common cocklebur plants grown within the soybean row compared to plants grown without interference. At harvest, soybean yield was reduced up to 40 to 50 cm within the row from individual cocklebur plants. The maximum distance of interference on one side of individual cocklebur plants was 75 cm. One cocklebur plant reduced soybean yield 16.0% within 1.5 m of soybean row as the result of full-season interference. Interference of common cocklebur plants spaced 60 cm apart within the row overlapped and caused an additive reduction in soybean seed yield. Across all cocklebur treatments, there was a consistent ratio of approximately 1 kg/ha loss in soybean seed yield for each 4 kg/ha of cocklebur herbage produced.
Factors Affecting Goatweed (Scoparia dulcis) Seed Germination
Authors: Jain Rakesh , Singh Megh
Published: May 2019

Goatweed seeds require light for germination, with optimum germination occurring at 25/20 or 30/25 C day/night temperatures. Germination was 8.5% 7 days after incubation at 20/15 C. At 15/10 C, no germination occurred, irrespective of the light treatment. Chilling at 4 C for 10 days prior to incubation at 30/25 C did not induce germination of dark-incubated seeds and had no effect on germination of light-incubated seeds. A photoperiod of at least 1 h daily was required to induce germination. Maximum germination, however, occurred with a 9-h photoperiod. Light intensity as low as 25 μE·m–2·s–1induced germination of goatweed seeds. Germination percentage increased with an increase in light intensity. Treatment with 1 mM gibberellic acid or 10 or 100 mM sodium nitrate or ammonium nitrate solution was effective in enhancing germination of light-incubated seeds, but not in inducing germination of dark-incubated seeds. Ammonium nitrate at 10 and 100 mM was more effective than sodium nitrate at the same concentrations in enhancing germination of goatweed seeds in the light. Ammonium chloride did not increase percent germination over that of seeds incubated in distilled water in the light. Germination percentage was maximum at pH 10 and at osmotic potentials 0.0 MPa.
Response of Monocot and Dicot Weed Species to Fresnel Lens Concentrated Solar Radiation
Authors: Johnson David W. , Krall James M. , Delaney Ronald H. , Pochop Larry O.
Published: May 2019

Fresnel lenses are used to concentrate solar radiation to a line or point. A linear Fresnel lens (0.91 by 1.52 m, 0.74-m focal length, 0.01- by 1.52-m line focus) was investigated as a method for weed control. Field experiments were conducted to assess the effect of Fresnel lens concentrated solar radiation at various exposure times, stages of plant growth, and soil surface moisture conditions. On a dry soil surface exposure times of 1 to 10 s at 290 C resulted in control of redroot pigweed from 100% for a 1-s exposure at the cotyledon stage to 89% for a 10-s exposure at the 10-leaf stage. Redroot pigweed and kochia control was similar at exposures of 3 to 10 s, but less for kochia at 1 and 2 s. Green foxtail control was less than that of kochia and redroot pigweed. Control was reduced on a moist compared to a dry soil surface. Concentrated solar radiation holds the greatest potential for control of small dicot weeds on a dry soil surface.
Four Foliar Pathogenic Fungi for Controlling Seedling Johnsongrass (Sorghum halepense)
Authors: Chiang Mou-Yen , Van Dyke C. G. , Chilton W. S.
Published: May 2019

Johnsongrass seedlings were inoculated with conidia of four fungi,Exserohilum turcicum(Et),Colletotrichumgraminicola (Cg),Gloeocercospora sorghi(Gs), and/orBipolaris halepense(Bh). Leaf injury from Et was the most extensive. Johnsongrass was equally or more susceptible to these fungi 7 days after emergence (DAE) than at 14, 21, or 28 DAE. The greatest leaf injury, more than 90%, was induced by Et with 2 × 105conidia/ml and a 24-h dew period. Sequential inoculation with Et at 15 and 20 DAE resulted in injury to more leaves than a single inoculation 15 DAE. No synergistic or antagonistic effects were observed in combinations of Et with Gs or Cg. Injury was limited to exposed leaves and sheaths, injured seedlings resumed growth and developed new leaves. Development of new leaves from inoculated plants was reduced by 30% or less at 14 days after inoculation (DAI) compared to uninoculated plants. Inoculation with Et or Bh was not as effective as paraquat or sethoxydim, since treatment with both herbicides resulted in seedling death. Seedling kill was not observed in any fungal tests.
Bioassay of Photosynthetic Inhibitors in Water and Aqueous Soil Extracts with Eurasian Watermilfoil (Myriophyllum spicatum)
Authors: Selim Salah A. , O'Neal Steven W. , Ross Merrill A. , Lembi Carole A.
Published: May 2019

Eurasian watermilfoil, an aquatic flowering plant, was found to be a suitable bioassay plant for the detection of photosynthetic inhibitor herbicides in water and aqueous extracts of soil. Stock cultures of Eurasian watermilfoil were maintained in an algal-free medium under constant environmental conditions. Oxygen evolution from three lateral shoots 3 to 5 cm in length was measured before and after herbicide treatment. Inhibition of photosynthesis was detected within 10 min of treatment. Concentrations as low as 5.9 × 10–8M terbacil and 6.4 × 10–8M diuron were detected in water. Simazine, atrazine, and metribuzin were detected in water at a concentration of 10–7M. Eurasian watermilfoil bioassays in lake water spiked with various concentrations of terbacil, metribuzin, atrazine, and simazine indicated that the bioresidual activity of these chemicals can be estimated in samples of natural water without extraction or purification. Using aqueous extracts taken from herbicide-treated soil, the Eurasian watermilfoil bioassay detected minimum levels of 0.047 and 0.07 kg/ha terbacil and atrazine, respectively. Neither soybean nor oat showed visible injury symptoms at these concentrations. The Eurasian watermilfoil bioassay has the advantage of being more rapid and/or more sensitive than methods using algae, oat seedlings, or leaf discs.
Toxicity, Absorption, Translocation, and Metabolism of Foliar-Applied Chlorimuron in Yellow and Purple Nutsedge (Cyperus esculentusandC. rotundus)
Authors: Reddy Krishna N. , Bendixen Leo E.
Published: May 2019

Greenhouse and laboratory experiments were conducted to study the activity of foliar-applied chlorimuron in yellow and purple nutsedge. Foliar-applied chlorimuron caused injury to both yellow and purple nutsedge at rates as low as 5 g ai/ha. Visible injury increased as rates increased from 5 to 20 g/ha at all weekly evaluation dates. At 28 days after application, there was 84% control of yellow and 100% control of purple nutsedge from 20 g/ha of chlorimuron. In both species, all rates of chlorimuron reduced shoot dry weight, inhibited secondary shoot production, and inhibited resprouting of parent tubers attached to treated plants. Over 92% of the applied label was recovered, when 15 μl of 3.46 mM14C-chlorimuron solution containing 0.18 μCi was applied to a 1 cm2area in the middle of the fourth fully expanded leaf. Over 12% of the total14C applied was absorbed, with over 15% of that being translocated within 1 day after application in both species. More than 76% of the absorbed14C in yellow nutsedge and 72% in purple nutsedge remained in the treated area. In both species, basipetal transport was limited. Analysis of plant tissue extracts by thin-layer chromatography indicated slow degradation of chlorimuron in both species. Susceptibility of yellow and purple nutsedge to chlorimuron appears to be due to the rapid absorption and translocation rates in relationship to the slow degradation rate of the active parent compound.
Inhibition of Chloroplast-Mediated Reactions by Quizalofop Herbicide
Authors: Ruizzo Michael A. , Gorski Stanley F.
Published: May 2019

A mechanism of action of the ethyl ester of quizalofop was determined in monocotyledonous and dicotyledonous plants. Quizalofop inhibited electron transport in both cucumber and corn chloroplasts. In corn, inhibition of electron transport was more pronounced under phosphorylating conditions. Half-maximal inhibition (I50) of ATP synthesis was achieved with a 75-μM concentration of quizalofop in coupled corn chloroplasts. Cucumber chloroplast ATP synthesis was not inhibited at herbicide concentrations up to 100 μM. Corn chloroplast fractions contained greater quantities of bound [U-14C] quizalofop ester following incubation in light and dark assays. Thin-layer radiochromatograms of14C-labeled quizalofop showed no metabolism or degradation of parent ester incubated in light and dark chloroplast-mediated reactions. In our studies, it is apparent that the inhibitory action of quizalofop was due to the parent ester. The ester formulation of quizalofop appears to exhibit multiple activity in susceptible plant chloroplasts.
Broadleaf Signalgrass (Brachiaria platyphylla) Duration of Interference in Rice (Oryza sativa)
Authors: McGregor John T. , Smith Roy J. , Talbert Ronald E.
Published: May 2019

Interference from broadleaf signalgrass at a density of 180 plants/m2reduced rough rice yields of ‘Bond’ a maximum of 48% at 95 days after rice emergence and reduced yields of ‘Mars' a maximum of 21% from season-long interference. Interference durations of 40 days or longer reduced the panicles/m2, culms/m2, and plant height of rice. Straw dry weight of Bond and Mars was reduced 41 and 26%, respectively, from season-long interference. Increased durations of weed interference did not affect the number of spikelets/panicle, percent filled spikelets, rough kernel weight, or head rice yield of either cultivar. Broadleaf signalgrass produced less dry weight and fewer panicles/m2when grown with Mars than with Bond.
Effects of Temperature and CO2Concentration on the Growth of Cotton (Gossypium hirsutum), Spurred Anoda (Anoda cristata), and Velvetleaf (Abutilon theophrasti)
Authors: Patterson David T. , Highsmith Maxine T. , Flint Elizabeth P.
Published: May 2019

Cotton, spurred anoda, and velvetleaf were grown in controlled-environment chambers at day/night temperatures of 32/23 or 26/17 C and CO2concentrations of 350 or 700 ppm. After 5 weeks, CO2enrichment to 700 ppm increased dry matter accumulation by 38, 26, and 29% in cotton, spurred anoda, and velvetleaf, respectively, at 26/17 C and by 61, 41, and 29% at 32/23 C. Increases in leaf weight accounted for over 80% of the increase in total plant weight in cotton and spurred anoda in both temperature regimes. Leaf area was not increased by CO2enrichment. The observed increases in dry matter production with CO2enrichment were caused by increased net assimilation rate. In a second experiment, plants were grown at 350 ppm CO2and 29/23 C day/night for 17 days before exposure to 700 ppm CO2at 26/17 C for 1 week. Short-term exposure to high CO2significantly increased net assimilation rate, dry matter production, total dry weight, leaf dry weight, and specific leaf weight in comparison with plants maintained at 350 ppm CO2at 26/17 C. Increases in leaf weight in response to short-term CO2enrichment accounted for 100, 87, and 68% of the observed increase in total plant dry weight of cotton, spurred anoda, and velvetleaf, respectively. Comparisons among the species showed that CO2enrichment decreased the weed/crop ratio for total dry weight, possibly indicating a potential competitive advantage for cotton under elevated CO2, even at suboptimum temperatures.
Interactions Between Soybean (Glycine max) Cultivars and Selected Weeds
Authors: Monks David W. , Oliver Lawrence R.
Published: May 2019

Competition of weeds was characterized by determining the distance down the soybean row that a weed affects soybean biomass and yield. Field studies were conducted for 2 yr to compare competitive effects of common cocklebur, johnsongrass, Palmer amaranth, sicklepod, and tall morningglory on ‘Forrest’ and ‘Centennial’ soybeans. The weeds did not significantly reduce soybean biomass for 6 weeks after emergence. Palmer amaranth, common cocklebur, and tall morningglory had the greatest biomass by 6 weeks after emergence. However, only competition from common cocklebur and Palmer amaranth measurably reduced soybean biomass during the growing season. Biomass of Forrest and Centennial soybeans was reduced when these cultivars were growing within 12.5 and 50 cm of common cocklebur, respectively. Johnsongrass, sicklepod, and tall morningglory grew more slowly than the other weeds and had no measurable competitive effects on soybean biomass. Soybean competition reduced biomass of all weeds 90 to 97%. Soybean cultivar influenced the level and duration of competitiveness depending on the weed species present. Biomass of both soybean cultivars was reduced when they were growing within 50 cm of Palmer amaranth. Soybean seed yield was reduced when soybeans were growing within 25 cm of common cocklebur and Palmer amaranth and also when they were growing within 12.5 cm of tall morningglory. Sicklepod had no effect on soybean seed yield.
Suppression of Red Rice (Oryza sativa) Seed Production with Fluazifop and Quizalofop
Authors: Salzman Frederick P. , Smith Roy J. , Talbert Ronald E.
Published: May 2019

Field research was conducted in 1985 and 1986 to compare the efficacy of fluazifop and quizalofop on production of panicles and seeds of red rice. Single and first sequential treatments were applied to red rice in the early-tillering, midtillering, and panicle initiation stages of growth. Sequential treatments were applied 14 days after each earlier application to red rice in the midtillering, late-tillering, and early-heading growth stages, respectively. Both herbicides were applied singly or sequentially at 70, 140, and 280 g/ha. Sequential applications of fluazifop and quizalofop at 280 g/ha caused the greatest reduction of red rice panicle and seed production. Fluazifop at 280 g/ha applied sequentially reduced panicle production 75 to 80% and seed production 80%; 140 g/ha applied sequentially reduced seed production 83%. Quizalofop at 280 g/ha applied sequentially reduced panicle production 75 to 100% and seed production 91%. Sequential applications of either herbicide applied to red rice plants in the panicle initiation and early-heading growth stages were the most effective treatments.
Influence of Environmental Factors and Adjuvants on the Foliar Penetration of Acifluorfen in Velvetleaf (Abutilon theophrasti): An Analysis Using the Fractional Factorial Design
Authors: Willingham Gary L. , Graham Linda L.
Published: May 2019

Two-level fractional factorial design experiments were conducted in growth chambers to determine the influence of environmental factors and adjuvants on the foliar penetration of the sodium salt of acifluorfen in velvetleaf. Relative humidity (RH) was found to have the greatest effect on penetration. Temperature was the second most important factor. Although soil moisture significantly affected penetration, this effect was much less than that produced by RH and temperature. Diammonium phosphate (DAP) was the most effective adjuvant tested. The use of DAP at 1.12 kg/ha significantly increased penetration. The effect of DAP was less than either RH or temperature. Oxysorbic (5 POE) surfactant also significantly increased penetration. Glycerol and oxtoxynol (7 to 8 POE) surfactant had no effect on penetration. In separate experiments, acifluorfen penetration at low and high RH and with the addition of DAP was measured to verify these results. Acifluorfen penetration into velvetleaf increased approximately ninefold with changes in RH from low to high. Penetration increased sevenfold when DAP was added. DAP was by far the most effective adjuvant increasing acifluorfen penetration into velvetleaf under conditions of low RH. Oxysorbic (5 POE) surfactant slightly increased penetration under these conditions.