Fluometuron adsorption and dissipation under field and laboratory conditions, and distribution within the soil profile was determined in 3 soils from Tennessee, Mississippi, and Georgia that are representative of the cotton-growing regions of the southeastern United States. Fluometuron adsorption was correlated with organic matter, but not with clay content or soil pH. First-order kinetics explained fluometuron dissipation under field and controlled conditions (r 2 ≥ 0.82). Field dissipation of fluometuron was slower under dry conditions. Fluometuron was not detected below 15 cm in the soil profile in any soil, and concentrations in the 8- to 15-cm soil zone were < 15 ppbw 112 d after treatment. Fluometuron dissipation was more rapid in soil from the 0- to 8-cm depth in Tennessee soil than in Mississippi soil under controlled conditions. Dissipation was more rapid under field conditions than under laboratory conditions at 2 of 3 locations. Fluometuron half-lives in soils from the 0- to 8-cm depth ranged from 9 to 28 d under field conditions and from 11 to 43 d in the laboratory. Fluometuron dissipation in soils from 30- to 45- and 60- to 90-cm depths was not different among soils, with half-lives ranging from 58 to 99 d under laboratory conditions. Fluometuron half-life was positively correlated with soil depth and inversely correlated with organic matter. These data indicate that organic matter, soil depth, and environmental conditions affect fluometuron dissipation.

Honey mesquite [Prosopis juliflora (Swartz) DC. var. glandulosa (Torr.) Cockerell], huisache [Acacia farnesiana (L.) Willd.], Macartney rose (Rosa bracteata Wendl.), live oak (Quercus virginiana Mill.), and whitebrush (Aloysia lycioides Cham.) were sprayed with herbicides alone and in mixtures. Mixtures of picloram (4-amino-3,5,6-trichloropicolinic acid) + dicamba (3,6-dichloro-o-anisic acid) at 0.56 + 0.56 and 1.12 + 1.12 kg/ha were most effective for killing honey mesquite in July. Picloram or picloram + dicamba were more effective for defoliating huisache than 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], dicamba, or other mixtures of herbicides. On Macartney rose picloram as the salt or ester was most effective, but some mixtures of picloram plus either 2,4-D [(2,4-dichlorophenoxy)acetic acid] or 2,4,5-T were as effective as picloram alone. On live oak, the most effective treatments generally contained at least 1.12 kg/ha of picloram either alone or in mixtures with dicamba or 2,4,5-T. Picloram alone killed as many or more whitebrush plants than MCPA [[(4-chloro-o-tolyl)oxy]acetic acid], dicamba, 2,4,5-T, 2,4-D, or mixtures.

Field experiments were conducted during the winters of 1987–88 and 1988–89 at Haryana Agricultural University, Hisar, India to evaluate the response of winter wild oat to sowing date and isoproturon application time in wheat. In another experiment, the effect of sowing time on emergence and growth of winter wild oat and wheat sown separately was studied. The treatments that provided more than 75% control of winter wild oat were: isoproturon at 0.75 kg ha−1 applied at the 2-leaf stage of winter wild oat; isoproturon 1 kg ha−1 applied at the 4-leaf stage of winter wild oat in the November 30 planting; and isoproturon 0.50 kg ha−1 applied at the 1- to 2-leaf stage of winter wild oat in the December 20 sowing. Isoproturon did not provide more than 50% control of winter wild oat in the November 10 sowing. Mortality of winter wild oat increased from 38 to 72 to 87% in November 10, November 30, and December 20 sowings, respectively. Mortality of winter wild oat was similar in November 30 and December 20 sowings but higher grain yield was recorded in November 30 sowing. Due to vigorous growth of winter wild oat in the November 10 sowing, isoproturon did not provide good control. December 20 sowing favored wheat growth due to lower density and late emergence of winter wild oat but reduction in wheat grain yield was greater. When averaged over isoproturon treatments, the grain yield of wheat was 4607, 5297, and 4457 kg ha−1 in the November 10, November 30, and December 20 sowings, respectively.

Laboratory and greenhouse experiments were conducted to examine the absorption and fate of quinclorac in field bindweed and to assess the importance of quinclorac soil activity for field bindweed control. No foliar absorption of 14C-quinclorac occurred when applied alone, but absorption increased to 24% when quinclorac was applied with 2,4-D, 28% urea ammonium nitrate (UAN), and methylated seed oil (MSO). Quinclorac translocation in field bindweed was limited, as < 18% of the total amount of absorbed radiolabeled material translocated out of the treated leaves 168 hours after treatment (HAT). Quinclorac metabolism in the treated leaves was minimal; 95% of the recovered 14 C was intact herbicide 168 HAT. Quinclorac soil activity on field bindweed was demonstrated in preemergence and soil subsurface applications. Preemergence application of 35, 70, 140, or 280 g ha−-1 quinclorac reduced field bindweed shoot growth. Field bindweed shoots exhibited auxinic herbicide symptoms at all quinclorac rates. Subsurface layering of quinclorac below the root system at rates of 35 and 280 g ha−-1 also reduced shoot and root growth. Both herbicide rates induced malformation in root structure with a proliferation of lateral branching, swollen and fused root tips, and malformed root buds. Shoot growth from surviving roots replanted in untreated media was also reduced in both herbicide treatments. These findings suggest quinclorac soil activity may be important for field bindweed control.

Field studies were conducted in three site-years to measure no-till Glycine max yield loss in relation to Apocynum cannabinum vegetative shoot density. Apocynum cannabinum densities of 28 to 40 shoots m−2 reduced predicted G. max yield 58 to 75% and 62 to 94% with the rectangular hyperbolic and linear regression models, respectively. Differences between locations were attributed to rainfall and temperatures, with delayed G. max canopy closure and higher yield loss where soil moisture remained high and temperatures were relatively cool. Application of these predictive G. max yield loss equations to field populations of A. cannabinum showed that between 19 and 36% and 20 and 29% G. max yield loss could be expected from within A. cannabinum patches for the rectangular hyperbolic and linear regression models, respectively. The rectangular hyperbolic regression model appeared to describe the relation between G. max yield loss and A. cannabinum density accurately; however, the model appeared to be dominated by the initial linear phase. This may indicate a lack of high levels of intraspecific competition among A. cannabinum shoots. The results of this study indicate that there is a strong linear relation between G. max yield loss and A. cannabinum shoot density. We conclude that the biological basis for the use of the rectangular hyperbolic model for creeping perennial weeds is questionable.

The effects of soil organic matter, clay, extractable Al, cation exchange capacity, and pH on the adsorption of picloram (4-amino-3,5,6-trichloropicolinic acid) from aqueous and surfactant solutions were investigated. Linear adsorption isotherms for the soils were obtained with the Freundlich equation. Of the five soil properties investigated, Freundlich K values correlated with extractable Al and clay content. Picloram adsorption from aqueous solutions and from the non-ionic and anionic surfactant solutions was greater on the soils at pH 5 than at pH 7. The anionic surfactant competed with picloram for adsorption sites on the soils at pH 5. Picloram adsorption from solutions containing 0.1 and 1% cationic surfactant was greater than that from aqeuous and anionic and nonionic surfactant solutions. Picloram adsorption from the 10% cationic surfactant solution was similar on soils with pH 5 and 7 and increased with decreased organic matter content.

Field research was conducted in Tennessee at two locations over 3 yr under no-tillage conditions to examine the interaction of broadleaf signalgrass and corn yield. Broadleaf signalgrass was killed at various time intervals during the growing season by applying postemergent glyphosate. Corn injury was avoided by the use of a glyphosate-tolerant variety. Yield reductions because of broadleaf signalgrass interference occurred with weed densities > 150 plants m−2 and when the corn and weeds emerged simultaneously. Corn had the ability to withstand broadleaf signalgrass presence up to 28 d after planting with no yield loss at all locations.

Field studies were conducted at four locations in North Carolina in 1998 and 1999 to evaluate a computer program, Herbicide Application Decision Support System (HADSS™), for weed management in peanut (Arachis hypogaea). Weed management systems included metolachlor or ethalfluralin preplant-incorporated (PPI) used alone or in combination with diclosulam preemergence (PRE) or flumioxazin PRE. These herbicide combinations were used alone, followed by (fb) postemergence (POST) herbicides recommended by HADSS™ or fb a standard POST program of paraquat plus bentazon early postemergence (EPOST) fb acifluorfen plus bentazon POST. The standard POST herbicide system and HADSS™ POST recommendations were also used without soil-applied herbicides. Ethalfluralin PPI alone controlled large crabgrass (Digitaria sanguinalis) better than metolachlor PPI. Combinations of metolachlor or ethalfluralin PPI with either diclosulam or flumioxazin PRE provided equivalent control of all weeds evaluated except yellow nutsedge (Cyperus esculentus). The addition of diclosulam or flumioxazin PRE to systems containing metolachlor or ethalfluralin PPI always improved control of ivyleaf morningglory (Ipomoea hederacea) and yellow nutsedge and improved yield and net returns in 15 of 16 comparisons where no POST herbicides were used. For systems that used diclosulam or flumioxazin PRE, the HADSS™ POST and standard POST herbicide systems improved yield in 4 of 12 and 2 of 12 comparisons, respectively, compared with similar systems that did not use diclosulam or flumioxazin. However, in systems using either HADSS™ POST or the standard POST system, yield was always improved when compared with metolachlor or ethalfluralin PPI alone. HADSS™ POST provided equal or higher weed control, peanut yield, and net returns when compared with the standard POST herbicide system.

Florida beggarweed is native to the Western Hemisphere but is naturalized around the world. During the last century, the mechanization of agriculture has transitioned Florida beggarweed from an important forage component to a weed of significance in the coastal plain of the southeast United States. This herbaceous annual is naturalized and found in fields and disturbed areas throughout the southern United States. The characteristics that made Florida beggarweed a good forage crop also make it a formidable weed. This review describes the importance of Florida beggarweed as a weed in the southern United States and the taxonomy of this species and details the distribution throughout the world and within the United States. The ecology of Florida beggarweed and its interactions with crop plants, insects, nematodes, and plant pathogens also are summarized. Finally, management of Florida beggarweed in agricultural systems using cultural practices and herbicides is reviewed.

Greenhouse and field experiments were conducted to examine foliar absorption and activity of nicosulfuron and primisulfuron by quackgrass with various adjuvants. Foliar absorption of 14C-nicosulfuron and 14C-primisulfuron plus petroleum oil adjuvant (POA) was completed by 4 h after application. Absorption of nicosulfuron plus POA and primisulfuron plus POA increased from 11 and 2% of applied, respectively, to 51 and 12% with the addition of urea-ammonium nitrate liquid fertilizer (UAN). At least 83% of the absorbed 14C from either herbicide penetrated the leaf epicuticular waxes. Absorption of 14C-labeled herbicides was greatest with the following adjuvants: POA + UAN > nonionic surfactant (NIS) + UAN = methylated seed oil. The addition of UAN to either NIS or POA significantly increased 14C-herbicide uptake. In greenhouse studies, nicosulfuron and primisulfuron applied with POA plus UAN provided greater quackgrass control than with POA alone. Despite the differences in foliar uptake in the greenhouse, few differences were observed between these adjuvants in 1989 or 1990 field efficacy trials. Quackgrass control was reduced by the addition of atrazine to nicosulfuron plus POA in 1989 and to primisulfuron plus POA in 1990. Combinations with atrazine did not reduce 14C-nicosulfuron or 14C-primisulfuron uptake by quackgrass.

Populations of large-flowered taxa of Carduus from many locations in the United States and Canada were grown in a common nursery from 1975 to 1983 at Lincoln, NE. Dates of first bloom and associated degree-day accumulation data exhibited some consistent relationships. Four species appeared to be represented in the collection. These included Carduus thoermeri Wein., C. macrocephalus Desf., and musk thistle (C. nutans L. ♯ CRUNU). A collection from British Columbia should be accorded species status but apparently has not been named in the literature. Interbreeding has taken place in the nursery and these combinations are intermediate between C. thoermeri and C. macrocephalus and between C. thoermeri and the British Columbia material. Some morphological characteristics supported these separations.

At the end of the cropping season in November 1994, Striga hermonthica seed populations were collected in northern Bénin (in the Atacora and Borgou departments). Host crops included Zea mays L. (corn), Pennisetum americanum (pearl millet), and Sorghum bicolor (L.) Moench (sorghum). The seed populations were kept dry in the laboratory, and germination was tested regularly after 2 wk conditioning in the laboratory. The seeds passed through a state of primary dormancy, which was not the same for seed populations collected from Z. mays and S. bicolor fields and those collected from P. americanum fields. The length of the primary dormancy was approximately 6 mo. After passing through primary dormancy (after-ripening), the seeds later went through annual, recurrent states of secondary dormancy. Primary dormancy coincided with the dry season directly after maturity (i.e., between December 1994 and April 1995), and secondary dormancy coincided more or less with the subsequent 1995/1996 and 1996/1997 dry seasons. It is concluded that the secondary dormancy pattern was endogenous. Germination percentages during the period that coincided with the first rainy season after collection were generally higher than during the period that coincided with the second rainy season.

Previous greenhouse studies with a noncommercial glyphosate-resistant sugarbeet variety indicated that susceptibility to Rhizoctonia crown and root rot could increase after glyphosate was applied. Greenhouse and field experiments were conducted in 2008 and 2009 to determine if glyphosate influenced disease severity in potential commercially available varieties of glyphosate-resistant sugarbeet. In the first greenhouse experiment in 2008, Hilleshög 9027RR, the most tolerant variety to Rhizoctonia crown and root rot, exhibited an increase in disease severity when glyphosate was applied. There were no significant differences between herbicide treatments in Hilleshög 9028RR, and glyphosate decreased disease severity in Hilleshög 9032RR when compared with the no-herbicide treatment. Experiments conducted to determine if glyphosate influenced Rhizoctonia solani growth in vitro indicated that glyphosate did not increase the radial growth of R. solani, except at 10× (190 µg ae ml−1) the normal rate of glyphosate plus ammonium sulfate (AMS). Field and additional greenhouse experiments were conducted using four commercial varieties. Differences in disease severity were observed when comparing varieties, but glyphosate did not significantly influence the severity of Rhizoctonia crown and root rot when compared with the no-herbicide control. Choosing a glyphosate-resistant sugarbeet variety with the best demonstrated tolerance to Rhizoctonia crown and root rot is an important factor in reducing disease severity and maintaining sugarbeet yield.

Common sunflower (Helianthus annuus L.) interference in onions (Allium cepa L. ‘Yellow Granex PRR’) was studied at different weed densities and periods of interference. Onion yields were reduced when the highest density (360/m2) of common sunflower interference with onions from 6 weeks after emergence and when sunflower at densities of 50/m2 and 5/m2 interfered for 12 and 15 weeks after emergence, respectively. Yield was not reduced if the crop was kept weed-free for 2 to 12 weeks after emergence with the shortest weed-free periods of 2 and 6 weeks requiring high light irradiance and high soil temperature and intermediate soil moisture. Climatic factors were more useful than weed density in explaining differential interference of sunflower in onions. Onion yield was negatively linearly correlated (P<0.05) with sunflower fresh weight, but was not linearly correlated with sunflower height.

Ivyleaf morningglory weed-free period, weedy period, and density studies were conducted in 1993 and 1994 to determine the effects of soil-applied imazaquin and chlorimuron plus metribuzin on ivyleaf morningglory interference in soybean. A weed-free period of 4 wk was needed to maintain soybean yield equivalent to weed-free season long when herbicides were not used, but treatment with either chlorimuron plus metribuzin or imazaquin maintained yield comparable to weed-free at all intervals. Ivyleaf morningglory biomass was reduced by both herbicides across all weed-free periods. The period nontreated ivyleaf morningglory plants were tolerated without yield loss was only 2 wk, but this interval was extended to 8 wk after treatment with chlorimuron plus metribuzin or imazaquin. Without herbicides, soybean yield was reduced by four ivyleaf morningglory per m of row, but the highest population evaluated in this study (eight per m of row) did not reduce soybean yield after treatment with chlorimuron plus metribuzin or imazaquin. Ivyleaf morningglory biomass was reduced at all densities after treatment with either herbicide.

The responses of whitebrush (Aloysia lycioides Cham.) and several associated species to herbicides were evaluated in the Central Basin and South Plains of Texas. At Llano, hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione], picloram (4-amino-3,5,6-trichloropicolinic acid), and tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea} were the most effective herbicides for whitebrush control. Picloram was the most effective herbicide on Lindheimer pricklypear (Opuntia lindheimeri Engelm.), tasajillo (Opuntia leptocaulis DC.), Texas colubrina [Colubrina texensis (Torr. & Gray) Gray], and Texas persimmon (Diospyros texana Scheele). Hexazinone, karbutilate [tert-butylcarbamic acid ester with 3(m-hydroxyphenyl)-1,1-dimethylurea], and tebuthiuron controlled live oak (Quercus virginiana Mill.). Tebuthiuron pellets were slightly more effective on whitebrush when applied broadcast than when applied in rows 1.8 to 6.0 m apart. Roller chopping alone did not kill whitebrush nor improve effectiveness of tebuthiuron but did improve access to the land and visibility for 3 yr. Picloram applied either as the undiluted liquid formulation or as granules was the most effective herbicide for controlling a spectrum of species, including whitebrush. Picloram pellets were generally more effective on Lindheimer pricklypear and Texas persimmon when applied broadcast than when applied in rows. However, tebuthiuron was the most effective herbicide on blackbrush acacia (Acacia rigidula Benth.) and huisache [Acacia farnesiana (L.) Willd.], especially when applied in rows rather than broadcast.

Nutrient-solution-grown pepper (Capsicum frutescens L. ‘Early Calwonder’) absorbed 62% of the diphenamid (N,N-dimethyl-2-2-diphenylacetamide) supplied via the roots for 48 h, and 74% in 150 h. Extensive translocation accompanied absorption, and 70 ± 3% of the absorbed 14C was present in shoots of plants harvested after 24- to 150-h treatments. Diphenamid was metabolized rapidly to chloroform-soluble and water-soluble compounds, and to unextracted residues. Chloroform-soluble compounds persisted for 150 h and accounted for more than 50% of the 14C in leaves. Water-soluble compounds other than N-hydroxymethyl-β-D-glycosides accounted for 25% of the water-soluble metabolites in leaves of nonfumigated plants. Ozone fumigation did not affect diphenamid absorption or translocation significantly. In leaves, ozone-enhanced accumulation of water-soluble metabolites more polar than N-hydroxymethyl-N-methyl-2,2-diphenylacetamide-β-D-glucoside (MDAG) and unextracted residues was observed. Ozone fumigation reduced the accumulation of these 14C-fractions in roots.

Accelerated degradation of the herbicide diphenamid (N,N-dimethyl-α-phenylbenzeneacetamide) was investigated in Israeli soils. Repeated application of this herbicide in the soil in the laboratory enhanced its degradation, which increased with an increasing number of applications. After the fourth application nearly 100% of the herbicide was degraded within 5 days of incubation, whereas only slight degradation was observed during the first 25 days in a previously untreated soil. Accelerated degradation was also observed in a soil collected from a field with previous diphenamid treatments. Fumigation with methyl bromide or treating the soil with the fungicide fentin acetate (triphenyltin acetate) was effective in decreasing the accelerated degradation of diphenamid, whereas the fungicides TMTD (tetramethylthiuram disulfide) and TBZ [2-(4-thiazolyl)benzimidazole] were only partially effective in inhibiting accelerated degradation. In the laboratory, fentin acetate prevented the degradation of diphenamid applied to previously untreated soil. Several fungi capable of degrading diphenamid were isolated from soils with or without accelerated degradation.

A washer was designed and tested for washing soil from weed seed buried in fabric packets and for separating weed seed from soil. The washer was constructed from inexpensive, readily available materials and was found to function efficiently.

Field and greenhouse experiments were conducted on bentazon [3-isopropyl-1H-2,1,3-benzothiadiazin-4(3H)one 2,2-dioxide] at 2.2 and 4.4 kg/ha and perfluidone {1,1,1-trifluoro-N-[2-methyl-4-(phenylsulfonyl) phenyl] methanesulfonamide} at 4.5 and 9.0 kg/ha for purple nutsedge (Cyperus rotundus L.) control and tolerance of five turfgrasses. A single application of each herbicide was applied to purple nutsedge, but single and repeated applications were applied to turfgrasses. Purple nutsedge control during the initial year of treatment was 98 to 100% when bentazon was applied in late spring, but the control was only 28 to 68% when applied in mid or late summer. Perfluidone controlled 76 to 87% of purple nutsedge when applied in late spring and 95 to 100% when applied in late summer. Bentazon treatments generally did not cause turf injury. In the field, perfluidone treatments injured St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze], zoysia grass (Zoysia japonica × Z. teniuflolia ‘Emerald’), centipedegrass [Erenoehloa ophiuroides (Munro) Hack.], and common bermudagrass [Cynodon dactylon (L.) Pers.]. ‘Tifway’ bermudagrass was generally tolerant to perfluidone treatments. In the greenhouse, perfluidone reduced the root growth of all turfgrasses except centipedegrass when compared with untreated checks.