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.

Greenhouse and field experiments, at two locations in Georgia, evaluated the tolerance of several soft red winter wheat cultivars (Triticum aestivum L.) to postemergence applications of metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one]. In the greenhouse, none of the cultivars growing in pots tolerated a 0.6 kg ai/ha treatment of metribuzin applied at the two-to three-tiller, six- to nine-tiller, or early-stem elongation growth stages. In nutrient culture, ‘McNair 1003’ was more tolerant to a 0.15 μg/ml concentration of metribuzin than other cultivars. Significant injury and yield reductions of wheat cultivars treated in the field with 0.6 and 1.1 kg/ha of metribuzin occurred. Differences between the cultivars were not uniform over all experiments. Increased injury was accompanied by higher rainfall and low temperatures subsequent to application. None of the wheat cultivars evaluated in the field experiments was injured by the 0.3 kg/ha rate of metribuzin. Acceptable selective weed control was obtained with this rate, indicating that metribuzin could be used in these soft red winter wheat cultivars.

Field experiments were conducted to determine the effects of various densities of four fall-seeded small grain mulches and diphenamid (N,N-dimethyl-α-phenyl benzeneacetamide) on weed control, yield, and quality in no-till flue-cured tobacco (Nicotiana tabacum L. ‘McNair 944’). A greenhouse study investigated the effects of non-soil-incorporated mulch from the same small grains plus alfalfa (Medicago sativa L.) on various growth parameters of tobacco (‘Speight G-70’). None of the mulches used in the greenhouse study adversely affected growth of the tobacco. Mulch from rye (Secale cereale L. ‘Abruzzi’) killed about 2 weeks before transplanting plus diphenamid provided better annual broadleaf weed control (85%) than wheat (Triticum aestivum L. ‘McNair’), barley (Hordeum vulgare L. ‘Keowee’), and no mulch. Oat (Avena sativa L. ‘Brooks’) mulch resulted in 80% broadleaf weed control. There were no differences in annual grass control (which was short lived) among mulches but control was lower in the no-mulch treatment. Rye mulch resulted in a 22% increase in the control of broadleaf weeds compared to no-mulch. Yield of the no-till tobacco did not differ among mulches and averaged 82% of that conventionally grown. The quality was not affected. The rye mulch did not affect the yield or quality of tobacco when compared to a nonmulch, noncultivated treatment. The 18% decrease in the no-till yield was apparently the result of the lack of tillage and increased weed interference and was not due to adverse effects from the rye.

The persistence of biologically active metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] and its ethylthio analog [4-amino-6-(1,1-dimethylethyl)-3-(ethylthio)-1,2,4-triazin-5(4H)-one] were compared using an intact-plant chlorophyll fluorescence bioassay technique with oats (Avena sativa L.) and wheat (Triticum aestivum L.). Degradation of metribuzin phytotoxicity at concentrations of 0 to 1 ppm (w/w) ai in a Pond Creek silt loam soil was linear over time, with a half-life of 8 days at 35 C. Initial degradation of the biologically active ethylthio analog was much more rapid than for metribuzin, with a decrease in rate at later time intervals. A quadratic function best described this degradation pattern. The initial degradation rate of phytotoxicity for the ethylthio analog indicated a half-life of 4 days at 35 C. Soil pH had no significant influence on the activity or persistence of either herbicide within the range 4.9 to 6.9.

The effects of tobacco thrips (Frankliniella fusca Hinds) control and herbicides on peanut (Arachis hypogaea L. ‘Florigiant’) canopy development and competition with large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] were examined in field experiments during 1983 and 1984. Greater early-season peanut canopy development generally occurred when tobacco thrips were controlled with aldicarb [2-methyl-2-(methylthio) propionaldehyde-O-(methylcarbamoyl)oxime]. Tobacco thrips control did not affect large crabgrass dry weights or peanut seed yields with no herbicide, alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], vernolate (S-propyl dipropylcarbamothioate) + benefin [N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine] + alachlor, and handweeding + sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio) propyl]-3-hydroxy-2-cyclohexen-1-one}. Averaged across weed control levels, large crabgrass dry weights with and without aldicarb were 320 and 310 g/m2 in 1983, and 260 and 250 g/m2 in 1984, respectively. Peanut seed yields with and without aldicarb were 1550 and 1630 kg/ha in 1983, and 2870 and 2920 kg/ha in 1984, respectively.

Preemergence applications of herbicides were evaluated for their effect on establishment of zoysiagrass (Zoysia japonica Steud.) with competition from either smooth crabgrass [Digitaria ischaemum (Schreb.) Muhl. # DIGIS] or goosegrass [Eleusine indica (L.) Gaertn. # ELEIN]. When ‘Meyer’ and ‘Belair’ zoysiagrass plugs were grown in sand and treated in the greenhouse, none of the herbicides reduced root weight or length. When plugs were grown in a Sassafrass sandy loam, bensulide {O,O-bis(1-methylethyl)-S-[2-[(phenylsulfonyl)amino] ethyl] phosphorodithioate} and simazine (6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine) reduced root weight, and simazine reduced root length of Belair, but not Meyer. In smooth crabgrass-infested field plots, more stolons were produced from Meyer plugs treated with simazine, oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one}, and siduron [N-(2-methylcyclohexyl)-N′-phenylurea] than plugs treated with bensulide, metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one], or the untreated control. At the end of two growing seasons, metribuzin-treated plots had significantly less zoysiagrass than other plots. Oxadiazon, DCPA (dimethyl tetrachloroterephthalate), and siduron enhanced the field establishment rate where Meyer zoysiagrass was competing with high populations of smooth crabgrass.

Diethatyl [N-(chloroacetyl)-N-(2,6-diethylphenyl) glycine] applied posttransplant in peppers (Capsicum annuum L.) but preemergence to hairy galinsoga [Galinsoga ciliata (Raf.) Blake # GASCI] controlled the weed at 1.7 to 2.2 kg ai/ha. No serious crop injury or yield reduction was observed when diethatyl was applied to peppers at 9 kg/ha posttransplant or at bloom. Soil ridging, practiced to improve drainage and control the crown rot phase of Phytophthora blight (Phytophthora capsici L.), limited the duration of weed control by disrupting the herbicide-treated surface soil and exposing untreated soil. Diethatyl applied at 2.2 kg/ha posttransplant and again at pepper bloom, after the soil ridges were formed, controlled hairy galinsoga throughout the entire growing and harvest season.

A method was developed for the quantitative determination of trace levels of the widely used herbicide sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} and its metabolites in an aqueous solution using reversed-phase high-performance liquid chromatography (HPLC). Optimum extraction of sethoxydim was with dichloromethane and was only 15% efficient at pH 3. The limit of detection by HPLC for sethoxydim was 5 ng on column and <5 ppb in soil. At least five different compounds were detected in the commercial formulation, in EPA reference standards, and in commercial sethoxydim standards. Sethoxydim undergoes a rapid decomposition in the presence of water to form more polar products, which accounts for the low extraction efficiency. Decomposition was greatest under alkaline conditions. Acid pH and soil inhibited decomposition and gave greater recoveries of parent compound. At least one breakdown product cochromatographed with a known sulfone derivative. The procedures are directly applicable to soils, environmental waters, and plant and animal tissues.

A fiber system for controlled delivery of fluridone {1-methyl-3-phenyl-5-[3-(trifluoromethyl)phenyl]-4(1H)-pyridinone} was evaluated for its potential use in the management of the submersed aquatic weed hydrilla [Hydrilla verticillata (L.f.) Royle # HYLLI] in slow-moving water. The release of fluridone from the fibers was first order and could be extended over several days simply by using fibers of larger diameters. Fibers of 0.8- and 1.2-mm diam released fluridone over a period of 40 and 50 days, respectively. Both effectively controlled hydrilla at a rate of 2.2 kg ai/ha in a 4-month study in replicated pools with water flow adjusted to provide one volume change every 24 h. Under the same conditions, the conventional liquid formulation was ineffective and a pellet formulation provided only marginal control.

A 2-yr field study was conducted to measure the growth and development of Russian thistle (Salsola iberica Sennen and Pau # SASKR) in the growing crops of winter and spring wheat (Triticum aestivum L.) and after harvest of these crops. In herbicide-free conditions, few Russian thistle seedlings emerged in winter wheat. Only 50% of these plants survived compared to 92 and 95% survival in spring wheat and crop-free treatments, respectively. Compared to growth in the crop-free treatment, both wheat types suppressed oven-dry weight, height, and width of Russian thistle plants during the crop-growing season and after crop harvest. During the crop-growing season, winter wheat suppressed Russian thistle height and width more than spring wheat. After crop harvest, oven-dry weight of Russian thistle plants grown in winter wheat stubble was suppressed 75% compared to plants grown in spring wheat stubble. Russian thistle plants grown in crop-free, spring wheat, and winter wheat treatments produced 152 100, 17 400, and 4 600 seeds/plant, respectively.

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.

Over 20 experiments comparing glyphosate [N-(phosphonomethyl)glycine], dicamba (3,6-dichloro-2-methoxybenzoic acid), fosamine [ethyl hydrogen (aminocarbonyl)phosphonate], and 2,4-D [(2,4-dichlorophenoxy) acetic acid] for control of field bindweed (Convolvulus arvensis L. # CONAR) were conducted from 1976 to 1982 at various times of the year and different stages of weed growth. In three of the studies, 1.7, 3.4, and 5.0 kg ae/ha of glyphosate gave 54, 72, and 80% control, respectively, 1 yr after application. Control with glyphosate at 3.4, 2,4-D at 1.1, dicamba at 1.1, and fosamine at 13.7 kg ae/ha in the 20 studies was 71, 55, 57, and 73%, respectively, 1 yr after application. Glyphosate, 2,4-D, and fosamine gave good control at any time of the year if weed growth was lush. Dicamba gave good control anytime if growth was good and in the fall regardless of growing conditions. Control with mixtures of dicamba and picloram, picloram and 2,4-D, or glyphosate and picloram was higher than with the other herbicides. Dicamba at 1.1 kg/ha, applied after August caused some injury to wheat planted the same fall. Herbicide combinations with picloram at 0.28 kg/ha applied after June injured wheat planted in the fall.

Ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. # IPOHE], planted in 1984 and 1985 the first of each month from April through August, began emerging in cotton (Gossypium hirsutum L. ‘Acala SJ-2’) 1 week after planting. Morningglory, at a density of 1 plant/2 m of row, emerging in April and May became so competitive to cotton by harvest in September that the total crop was lost. June plantings, although less competitive than earlier plantings, still reduced yields by 11%. Later plantings did not reduce yields of cotton. Morningglory plantings that produced seed (April through July) began flowering within 7 weeks, and viable seed was collected for the first time 9 weeks after planting. Ivyleaf morningglory plants that emerged in April and May produced about 11 000 seed/plant by cotton harvest. This compared to 3000 and 93 seed/plant for morningglory that emerged in June and July, respectively. The earliest that morningglory might be expected to produce seed in cotton planted in early April would be late May to early June, and morningglory emerging as late as the first of July could produce some seed by cotton harvest.

In order to find the most effective and economical method of incorporation, six preplant herbicides for cotton (Gossypium hirsutum L.) were incorporated with a tandem disk or field cultivator, or sprayed on unbedded soil prior to bedding with a disk bedder. These treatments were compared to incorporating sprayed beds with a rolling cultivator and no incorporation. A mixed population of pigweed (Amaranthus hybridus L. # AMACH and Amaranthus retroflexus L. # AMARE) was present each year. There was no significant difference in pigweed control among incorporation with a disk, field cultivator, or rolling cultivator. Puncturevine (Tribulus terrestris # TRBTE) and barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] were controlled best following rolling cultivator incorporation. Cotton lint yields were not affected by incorporation methods or herbicides. Economic analysis and weed control indicate that the field cultivator was the best way of incorporation.

Fluchloralin [N-(2-chloroethyl)-2,6-dinitro-N-propyl-4-(trifluoromethyl)benzenamine], pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine], and trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzenamine] either alone or in combination with fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy] propanoic acid}, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, or sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} were evaluated for johnsongrass [Sorghum halepense (L.) Pers. # SORHA] control in reduced-tillage soybean [Glycine max (L.) Merr.] production systems. Data obtained in 1983 and 1984 near Lexington and Princeton, KY, indicated that johnsongrass could be effectively controlled. A single discing before application of the soil-active herbicides usually had no effect on johnsongrass control. Johnsongrass control was primarily dependent on foliarly applied herbicides. Preplant-incorporated treatments did not provide adequate johnsongrass control when used alone. Johnsongrass panicle numbers recorded in September corresponded to visual evaluations of control recorded earlier in the growing season. Soybean yield with all herbicide treatments was greater than with a nontreated control and was closely associated with the degree of johnsongrass control.

The influence of various additives on the absorption and translocation of fluazifop {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl]oxy]phenoxy]propanoic acid} butyl ester in oats (Avena sativa L. var. ‘Lyon’) was determined. Fluazifop absorption and translocation by oats 48 h after application were less when applied with safflower (Carthamus tinctorius L.), sunflower (Helianthus annuus L.), soybean [Glycine max (L.) Merr.], linseed (Linum usitatissimum L.), and palm (Eleais quineeneis Jacq.) oil than with petroleum oil. However, fluazifop absorption and translocation continued to increase for the 96-h duration of the experiment when applied with soybean oil but only for 24 h when applied with petroleum oil. The 14C-fluazifop-label recovery was higher when applied with oils than when applied alone, which may have been due to reduced fluazifop volatility when it was emulsified with the oils. Absorption and translocation of fluazifop applied with glycerol or various emulsifiers were equal to or less than fluazifop absorption and translocation when applied with petroleum oils but were greater than fluazifop absorption and translocation when applied with seed oils 48 h after application. Fluazifop absorption and translocation were similar whether soybean or petroleum oil additives were applied with or without emulsifiers. Totally refined seed oils only slightly increased fluazifop absorption and translocation compared to fluazifop with once-refined or degummed seed oils.

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.

The weedy spurges found in the Delta region of Mississippi, U.S.A., include spotted spurge (Euphorbia maculata L. # EPHMA), nodding spurge (Euphorbia nutans Lag. # EPHNU), prostrate spurge (Euphorbia humistrata Engelm. ex Gray # EPHHT), creeping spurge (Euphorbia serpens H.B.K. # EPHSN), and hyssop spurge (Euphorbia hyssopifolia L. # EPHHS). Nodding spurge was the most common while creeping spurge was the least common. Hyssop spurge, not previously known to be in Mississippi, was found in six of the 17 counties in the Delta of Mississippi. Hyssop spurge occurs with, and had previously been confused with, nodding spurge. Diagnostic characters, special identification features, and illustrations are provided to aid in identification of these five species of weedy spurges, which occur widely in the U.S.

Field research was conducted in Nebraska to evaluate the efficacy of herbicides for the control of summer annual weeds in sorghum [Sorghum bicolor (L.) Moench.]. During 1976 to 1979, no-till plots treated with a mixture of paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], and terbutryn [N-(1,1-dimethylethyl)-N′-ethyl-6-(methylthio)-1,3,5-triazine-2,4-diamine] yielded 33% more sorghum grain than plots receiving the same herbicides when a seedbed was prepared by disking. During 1981 to 1983, season-long weed control was obtained with acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl) acetamide], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile}, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide], or terbutryn added to paraquat plus atrazine and metolachlor plus cyanazine plus paraquat applied 10 days prior to planting. The use of seed safeners did not increase sorghum yield.