Cotton [Gossypium hirsutum (L.) ‘Hancock’] lint yield or quality was not adversely affected under weed free conditions by three consecutive annual preemergence applications of up to 1.68 kg/ha fluometuron [1,1-dimethyl-3-(a,a,a-trifluoro-m-tolyl)urea] alone or in combination with 0.84 kg/ha trifluralin (a,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) preplant incorporated on silt loam soils of the Memphis catena containing less than 1% organic matter. Similar applications of fluometuron at 3.36 kg/ha delayed maturity of cotton plants and ultimately reduced lint yields. Trifluralin treatments tended to overcome the detrimental effects of high rates of fluometuron. There was no effect on fiber development and maturation because fiber length and fineness (micronaire) were virtually identical for all treatments. The effect on maturity as determined by percent first harvest was a reflection of slower plant growth and fruiting and not of the development of the fiber itself. These results indicate no detrimental effects on cotton yield, maturity, and quality from annual applications of these herbicides at rates recommended and normally used in Tennessee.

Field bindweed infests millions of hectares in the Great Plains greatly reducing productivity and value of land. The standard practice for field bindweed control is sweep tillage at 3 wk intervals combined with one or two annual 2,4-D) applications during the 14 mo fallow period in a winter wheat-fallow crop rotation. This was compared to tillage and 2,4-D in conjunction with dicamba or a mixture of picloram+2,4-D applied once during the first October of the first 14 mo fallow period. Also, three no-tillage systems were included using glyphosate+2,4-D at monthly intervals. Two of the treatments were supplemented with dicamba, or picloram+2,4-D as in the sweep tillage system. All treatments controlled field bindweed in two fallow periods and two winter wheat crops, and increased winter wheat yields to about twice the control. Sweep tillage at 3 wk intervals combined with 2,4-D resulted in $36 ha−1 profit for an owner-operator compared to $15 ha−1 loss with no herbicide or tillage treatment. On average no-tillage lost $35 ha−1. Other treatments, although controlling field bindweed, lost from 35 to $186 ha−1. To determine if long-term benefit after control was achieved, average yields for the area were used to calculate profits using normal farming practices. Profits were 136, 78, and $-50 ha−1, respectively, for sweep tillage and 2,4-D, no-tillage, and the untreated check. In a standard 33:67 owner-tenant rental, profits to the owner for the control period were 90, −33, and $43 ha−1, respectively for tillage and 2,4-D, no-tillage, and untreated check. The tenant lost from $24 to 69 ha−1 for the three systems indicating owners must modify rental agreements during a field bindweed control program.

Barnyardgrass is a problem in winter wheat fields in the central Great Plains following harvest. Glyphosate plus 2,4-D efficacy on barnyardgrass with or without atrazine was investigated under various watering events at three sites in west central Nebraska. Two experiments were initiated at each site. One experiment dealt with rainfall and the other rainfall plus irrigation. Main plots in stubble fields infested with barnyardgrass were sprayed with glyphosate plus 2,4-D at 0.4 plus 0.7, 0.5 plus 0.8, and 0.6 plus 1.0 kg ae ha−1 alone and with 2.2 kg ai ha−1 atrazine. Barnyardgrass was under drought stress in unwatered areas in 1991 at two sites, but the 1993 site was waterlogged. Glyphosate plus 2,4-D at 0.6 plus 1.0 kg ha1 controlled 62, 99, and 100% of the barnyardgrass at the three sites 30 DAT. Nevertheless, control was reduced to 48, 88, and 35% when atrazine was combined with glyphosate plus 2,4-D. Poorest control came when plants were under stress from drought or waterlogging and atrazine was included in the spray solution. In subplots barnyardgrass plants in a 0.8 m2 area were watered 6, 3, or 1 d before spraying and 1, 4, 7, or 11 d after spraying. By watering drought-stressed barnyardgrass 6 d before spraying, control generally was similar or better than with later watering dates. Watering 6 d before spraying with glyphosate plus 2,4-D plus atrazine at 0.6 plus 1.0 plus 2.2 kg ha−1 reduced but did not eliminate antagonism from atrazine.

The effects of an approximate 1:4 commercial mixture of 4-amino-3,5,6-trichloropicolinic acid (picloram) and (2,4-dichlorophenoxy)acetic acid (2,4-D) on a natural population of soil algae were studied at dosages of 0.28, 0.56, and 1.12 kg/ha of picloram. No change in the composition of the algal flora was noted over an 18-month period, regardless of dosage. In vitro studies indicated that mixtures of picloram and 2,4-D inhibited growth of Chlorella vulgaris Beyer. at concentrations above 100 ppm, but concentrations above 250 ppm were needed for growth inhibition of Cylindrospermum licheniforme (Bory) Kuetz. or Chlorococcum sp. Picloram alone inhibited all three algae at 50 ppm, while 2,4-D produced no inhibitory effects at concentrations less than 400 ppm.

Eighteen soil-active herbicides were evaluated for control of downy brome (Bromus tectorum L.) and associated broadleaf weeds during revegetation of big sagebrush (Artemisia tridentata Nutt.) rangelands in Nevada and in northeastern California. We rated all herbicides in reference to a chemical-fallow program for replacement of vegetation, where seeding follows and is separated from herbicide application by at least 1 year. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) applied at 1 lb/A was the most promising treatment with respect to three essential characteristics: length of activity, spectrum of weed control, and relative preemergence and postemergence phytotoxicity.

A greenhouse study was conducted to determine the effect of henbit and purple deadnettle density on weed biomass accumulation and soybean cyst nematode (SCN) reproduction. SCN did not impact shoot or root dry weight of purple deadnettle, henbit, or soybean. Foliar and root biomass of henbit and purple deadnettle were comparable but the biomass per stem was higher for purple deadnettle. Shoot and root biomass per pot of henbit and purple deadnettle at corresponding plant densities were statistically similar and were generally higher with increasing plant density. Henbit produced a greater number of stems than purple deadnettle and the least number of stems for both species existed at low densities. Purple deadnettle allowed for more SCN reproduction than did henbit. Weed densities also influenced SCN cyst and egg production but the results were species dependent. The highest SCN reproduction per pot was supported at low to moderate densities of purple deadnettle but at moderate to high densities of henbit. These results suggest that purple deadnettle should be more aggressively managed than henbit in management programs for SCN, but that henbit, especially at high densities, can support SCN reproduction at levels near those of purple deadnettle.

Application timing and environmental factors reportedly influence the efficacy of auxinic herbicides. In resistance-prone weed species such as Palmer amaranth (Amaranthus palmeri S. Watson), efficacy of auxinic herbicides recently adopted for use in resistant crops is of utmost importance to reduce selection pressure for herbicide-resistance traits. Growth chamber experiments were conducted comparing the interaction of different environmental effects with application time to determine the influence of these factors on visible phytotoxicity and hydrogen peroxide (H2O2) formation in A. palmeri. Temperature displayed a high degree of influence on 2,4-D and dicamba efficacy in general, with applications at the low-temperature treatment (31/20 C day/night) resulting in an increase in phytotoxicity compared with high-temperature treatments (41/30 C day/night). Application time across temperature treatments significantly affected 2,4-D–induced phytotoxicity, resulting in a ≥30% increase across rates with treatments at 4:00 PM compared with 8:00 AM. Temperature differential had a significant influence on dicamba efficacy based on visible phytotoxicity data, with a ≥46% increase with a high (37/20 C day/night) compared with a low differential (41/30 C day/night). Concentration of H2O2 in herbicide-treated plants was 34% higher under a high temperature differential compared with the low differential. Humidity treatments and application time interactions displayed undetected or inconsistent effects on visible phytotoxicity and H2O2 production. Overall, temperature-related influences seem to have the largest environmental effect on auxinic herbicides within conditions evaluated in this study. Leaf concentration of H2O2 appears to be generally correlated with phytotoxicity, providing a potentially useful tool in determining efficacy of auxinic herbicides in field settings.

Junglerice [Echinochloa colona (L.) Link] is a problematic weed in the northern grain region of Australia. Two pot experiments (Experiment 1 and Experiment 2) were conducted in a screen house to evaluate the growth and reproductive behavior of two biotypes (A, collected from a cotton (Gossypium hirsutum L.)–fallow; B, collected from a fence near a water channel) of E. colona in response to water stress (100%, 75%, 50%, and 25% water holding capacity [WHC]). Averaged across both biotypes, the plant height, biomass, and seed production of E. colona were reduced at 25% WHC compared with 100% WHC. However, E. colona still produced a considerable amount of seeds at 25% WHC (at least 365 seeds plant−1). Biotype A produced more seeds in the second experiment, while biotype B produced more seeds in the first experiment. In Experiment 2, at 100% WHC, biotype A produced more seeds (17,618 seeds plant−1) than biotype B (4,378 seeds plant−1), and similar observations were noticed for root biomass. Growth and seed production of E. colona at all moisture levels and environmental conditions ensure survival in an unpredictable environment and contribute to the weedy nature of this species. Results indicate that biotype A is more invasive than biotype B under favorable environmental conditions (100% WHC). This study suggests an enhanced competitive ability of some biotypes of E. colona in response to a range of environmental and soil moisture conditions in Australia. Under favorable environmental conditions, biotype A could be more problematic, as it has higher seed production than biotype B. Therefore, it is important to implement sustainable weed control methods for such biotypes in the early stages of crop growth to prevent loss of stored moisture.

Texas panicum (Panicum texanum Buckl.) seed were collected and treatments applied in an effort to increase germination. Also, plants were grown in the field and growth characteristics studied. Poor seed germination was obtained with all treatments, but wide variation in storage temperature produced the best germination. Seedlings emerged from seed planted as deep as 3 inches. An average of 118 heads per plant and 195 seed per head were produced, or 23,010 seeds per plant. Plant, seed head, and seed development followed sigmoid growth patterns. The species was resistant to most preplant and preemergence herbicides used in screening experiments.

Critical period experiments were conducted in 1997 near Milton, WI, and in 1998 near Edgerton, WI, in which Eriochloa villosa (Thunb.) Kunth emergence was characterized and related to Zea mays L. yield loss and weed seed production. At Milton, 2.7% of the spring seedbank emerged, and at Edgerton, 14.5% of the spring seedbank emerged. Peak time of E. villosa emergence occurred early in the season at both locations, accounting for 84% of the total season emergence at Milton by 37 d after planting and 90% of the total season emergence at Edgerton by 27 d after planting. A secondary peak in emergence occurred at each site, accounting for 14% of the total season emergence at Milton between 38 and 52 d after planting and 8% of the total season emergence at Edgerton between 28 and 43 d after planting. Following the secondary peak in emergence at each site, approximately 2% of the total season emergence occurred. Zea mays grain yield was reduced when E. villosa interfered with Z. mays past the V11 stage at Milton and the V3 stage at Edgerton. Zea mays yield reductions at Edgerton were greater, occurred under shorter periods of weed interference, and were associated with greater E. villosa biomass than yield reductions at Milton. Eriochloa villosa that emerged after the V2 Z. mays stage at Milton and the V3 stage at Edgerton did not cause crop yield loss; however, these plants produced seed at 143 and 63% of the initial spring seedbanks, respectively.

Purple nutsedge is considered to be the worst weed in the tropical and subtropical regions of the world. Although the plant is a low grower it has very strong competitive abilities. The influence of initial tuber size and cold treatment on tuber sprouting, accumulation of plant biomass and new tubers formation was studied. Tubers sprouted continuously over 30 to 50 d with significantly lower sprouting ability of small tubers (0.1 to 0.2 g). Short cold treatment (4 C for 4 d) significantly stimulated sprouting process. The early sprouting of cold treated tubers led to increased number of shoots and inflorescences and therefore more intensive biomass accumulation, as well as more intensive formation of new tubers. The increase in total biomass accumulation raises the reproductive and spreading potential of the weed.

Row spacing and the relative time of velvetleaf emergence affects the time of soybean canopy closure relative to velvetleaf, influencing the growth and development of velvetleaf. Field studies were conducted in northeastern Nebraska in 2002 and 2003 to describe velvetleaf growth as influenced by soybean presence or absence (velvetleaf grown with soybean or in monoculture), soybean row spacing (19 and 76 cm), and relative time of velvetleaf emergence. Velvetleaf seed production, leaf area (LA), and total dry matter (TDM) were greater in 76-cm- than in 19-cm-wide soybean rows. LA, TDM, and seed production of velvetleaf were reduced with later emergence times in both monoculture and with soybean. Velvetleaf LA, TDM, and seed production decreased when grown with soybean compared with when grown in monoculture. Practical implications of this study suggest that narrowing crop row spacing and controlling early-emerging velvetleaf in soybean can be an effective part of an integrated weed management strategy.

Land was prepared conventionally in early spring for the planting of small seeded legumes. Planting was delayed to allow emergence of weeds. We applied 1,1'-dimethyl-4,4'-bipyridinium salts (paraquat) and planted legumes immediately afterwards. Stage of weed growth, time of herbicide application, rate of chemical applied, and the methods of seeding were variables imposed. Paraquat (plus surfactant) applied at 1.1 and 2.2 kg/ha to emerged weeds prior to the seeding of legumes controlled quackgrass [Agropyron repens (L.) Beauv.] sufficiently to allow excellent establishment of alfalfa (Medicago sativa L.) and birdsfoot trefoil (Lotus corniculatus L.). A paraquat application delayed until yellow nutsedge (Cyperus esculentus L.) was at least 10 cm in height, followed by a disking, controlled the sedge sufficiently to allow legume establishment. For annual weed control, 0.3% kg/ha of paraquat was sufficient. Drilling as a method of seeding gave better legume stands than did surface-seeding techniques.

Field and laboratory studies were conducted to examine the influence of previous pesticide use, number of prior EPTC (S-ethyl dipropyl carbamothioate) and butylate [S-ethyl bis(2-methylpropyl)carbamothioate] applications, and pretreatment of soil with EPTC and butylate metabolites on EPTC and butylate degradation. EPTC degradation was enhanced in Clay Center and Scottsbluff soils following three annual EPTC, butylate, or vernolate (S-propyl dipropylcarbamothioate) applications, but was not affected in soils following three annual atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], 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], alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide], or cycloate (S-ethyl cyclohexylethylcarbamothioate) applications. EPTC degradation rate was not affected in a Scottsbluff soil following three annual carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) applications, but was partially enhanced in a Clay Center soil. Self- and cross-enhanced degradation of EPTC and butylate did not change regardless of the number of prior annual applications of each herbicide. The degradation rates of EPTC and butylate were not affected by soil pretreated with butylate sulfone, but the degradation rates-were fully enhanced by pretreatment with the respective sulfoxides of each herbicide. In cross-enhancement testing, EPTC and butylate degradation was partially enhanced in Clay Center soil pretreated with the sulfoxides of each.

Broadleaf species such as tanoak [Lithocarpus densiflorus (Hook. & Arn.) Rend.] and pacific madrone (Arbutus menziezii Pursh) reduced conifer growth on previously logged or burned areas of the northern California and southwest Oregon coast range. Cut-surface applications of 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], and picloram (4-amino-3,5,6-trichloropicolinic acid) into tanoak and pacific madrone growing as overstory to Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] were found to provide acceptable control for 10 years following application. Increment cores obtained from Douglas fir in treated and non-treated plots revealed substantial stem enlargement as a result of tanoak and pacific madrone control.

In experiments conducted at the International Rice Research Institute, Philippines, all commonly marketed formulations and derivatives of either [(4-chloro-o-tolyl)oxy]acetic acid (MCPA) or (2,4-dichlorophenoxy) acetic acid (2,4,D) performed in about the same way and were equally safe for use in controlling barnyardgrass [Echinochloa crusgalli (L.) Beauv.] and other annual weeds in transplanted rice (Oryza sativa L.). Eleven-day-old rice seedlings were more susceptible to amine salts of 2,4-D or MCPA than 21-day-old seedlings. Granular formulations of some chemicals were relatively less toxic than liquid formulations. The toxic effect of spraying the potassium salt of MCPA was less prolonged on the indica variety, IR22, than it was on the japonica variety, Chianung 242, which had delayed flowering and maturity.

A ‘tifgreen’ bermudagrass [Cynodon dactylon (L.) Pers.] golf-type green was treated with seven preemergence and one postemergence type herbicides at two rates each for three consecutive years to assess their phytotoxicity. A few herbicides were applied on a second, third, and fourth treatment date during the year with applications made in separate plots. Severe foliage injury occurred the first year with siduron [1-(2-methylcyclohexyl)-3-phenylurea] while moderate injury occurred with bromacil (5-bromo-3-sec-butyl-6-methyluracil) and DCPA (dimethyl tetrachloroterephthalate); and slight injury occurred with benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), bensulide [0,0-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide], and terbutol (2,6-di-tert-butyl-p-tolyl methylcarbamate). No injury was observed with bandane (polychlorodicyclopentadiene isomers) and tri-calcium arsenate. Injury to the bermudagrass in the second year following renewal treatments was severe with siduron and bromacil; moderate with benefin, bandane, DCPA, and terbutol; and slight with bensulide and tri-calcium arsenate. Injury in the third year following repeat applications was severe with siduron, terbutol, bandane, bromacil, benefin, and DCPA; slight to moderate with bensulide, and slight with tri-calcium arsenate. Injury observed the fourth year resulting from residues was moderate with bandane; slight with terbutol, benefin, bensulide, and DCPA; and none with siduron, bromacil, and tri-calcium arsenate.

Several herbicides applied either in the fall or spring at rates used for musk thistle (Carduus nutans L.) control had no deleterious effects on two cool-season grasses, smooth brome (Bromus inermis Leyss.) and intermediate wheatgrass [Agropyron intermedium (Host) Beauv.]. Herbicides used were 2,4-D [(2,4-dichlorophenoxy)acetic acid], 2,4,5-T [(2,4,5-trichlorophenoxy)acetic acid], dicamba (3,6-dichloro-o-anisic acid), picloram (4-amino-3,5,6-trichloropicolinic acid), triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid}, and Dowco 290 (3,6-dichloropicolinic acid). Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] was included for comparative purposes because it is known to affect the protein content of some forage grasses. Effects on the quality of the forages were measured by in vitro dry matter disappearance (IVDMD), protein and KNO3 determinations. Intermediate wheatgrass was less susceptible to damage from the highest rates of picloram and atrazine than smooth brome.

Smutgrass [Sporobolus poiretii (R. & S.) Hitchc.] in native grass and ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.] pastures near Caldwell, Texas, was sprayed with herbicides in 1975 and 1976. Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] at 4.5 kg/ha; dalapon (2,2-dichloropropionic acid) at 5.6 kg/ha; glyphosate [N-(phosphonomethyl)glycine] at 0.6 and 2.2 kg/ha; and bromacil (5-bromo-3-sec-butyl-6-methyluracil), tebuthiuron {N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N′-dimethylurea}, and hexazinone [3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione] at 1.1 and 2.2 kg/ha reduced smutgrass foliar cover, particularly if applied from July to November. Dalapon, tebuthiuron, and hexazinone were the most effective herbicides for reducing smutgrass foliar cover. Other grasses generally replaced smutgrass controlled with hexazinone or tebuthiuron, while broadleaf species mostly replaced smutgrass in plots controlled with dalapon or glyphosate. Dalapon, glyphosate, bromacil, hexazinone, and tebuthiuron caused some injury to Coastal bermudagrass for 3 or 4 months following treatment. By fall of the year after treatment Coastal bermudagrass cover in treated plots was equal to or greater than that in untreated plots.

The objective of this investigation was to determine if preemergence herbicides, applied at the standard rates and times for smooth crabgrass [Digitaria ischaemum (Schreb.) Muhl. ♯ DIGIS] control, would provide season-long control of goosegrass [Eleusine indica (L.) Gaertn. ♯ ELEIN] in the transition zone. The transition zone is a unique area of turfgrass culture between cool and warm regions where quality of turfgrasses frequently declines due to environmental stresses. Single and sequential applications of bensulide [O,O-diisopropyl phosphorodithioate S-ester with N-(2-mercaptoethyl)benzenesulfonamide] and DCPA (dimethyltetrachloroterephthalate) did not effectively control goosegrass in any of the three test years. Benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) usually required sequential dosages to provide good (90%) to excellent (95%) goosegrass control. Nearly all rates of oxadiazon [2-tert-butyl-4(2,4-dichloro-5-isopropoxyphenyl)-δ2-1,3,4-oxadiazolin-5-one] used provided good to excellent goosegrass control. Napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] plus bensulide provided excellent goosegrass control in 1981, but not in 1982. Pendimethalin [N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitrobenzenamine] also provided effective goosegrass control.