Foliar activity of the butyl ester of fluazifop on large crabgrass was determined by varying the concentration of a petroleum-based oil concentrate and the carrier volume. Increasing the concentration of petroleum oil or reducing the carrier volume improved large crabgrass control. Under greenhouse conditions, both visible injury and plant dry weight reflected greater control with adjuvant concentrations increasing from 0.62 to 5.0% v/v. Similarly, reducing carrier volumes from 374 to 47 L/ha increased grass control. No significant interaction between carrier volume and adjuvant concentration suggests the effects of these two variables are independent of one another. For both variables, effects were greater with sublethal rates of fluazifop.

Twenty determinate soybean cultivars were grown in hydroponic solutions to determine differential tolerance to chlorimuron and imazaquin at pH 6, 7, or 8. ‘Epps' exhibited tolerance to chlorimuron at each pH, and to imazaquin except at pH 8. ‘9641 Pioneer’ was highly sensitive to both herbicides at each pH, and ‘Asgrow 5979’ was sensitive to chlorimuron, and to imazaquin except at pH 7. ‘Hutcheson’ was sensitive to chlorimuron at each pH, and imazaquin at pH 6. ‘Asgrow 6785’ was sensitive to chlorimuron at pH 6 and 8, with shoot weight reductions of 31 and 28%, respectively, and ‘Coker 686’ was similarly sensitive at pH 6 and 7. ‘Hartz 6200’ was tolerant to imazaquin at pH 6 and 7, ‘Hartz 6686’ was tolerant at pH 6 and 8, and Coker 686 was tolerant at pH 7 and 8. Coker 686 and 'Sharkey’ were tolerant to chlorimuron at some pH levels, though highly sensitive at other pH levels. ‘Asgrow 5403’ and Coker 686 also had varying tolerance and sensitivity to imazaquin across pH levels. Shoot length and shoot weight were the best indicators of differential cultivar sensitivity when compared with previous field studies.

In 1988, mowing C. thoermeri once at the bud stage, twice at the bud stage, or once at early bloom of the primary inflorescences, eliminated emergence of Rhinocyllus conicus, a weevil introduced as a biological control agent. Mowing at full bloom reduced weevil survival by 78.8%, whereas mowing at senescence had no effect. In 1989, mowing at full bloom or senescence did not affect weevil survival. Dicamba applied at the full bloom or senescence stage did not affect R. conicus survival, whereas hexazinone reduced R. conicus survival when applied at all growth stages.

Sulfonylurea herbicide-resistant prickly lettuce was discovered in Idaho in 1987. The objectives of these surveys were to determine the change with time in the proportion of sulfonylurea resistant and susceptible prickly lettuce biotypes on the farm where it originally occurred, and to determine the spread of sulfonylurea resistant prickly lettuce beyond its point of origin. On average, the proportion of resistant plants had decreased from 1988 to 1990, a period when sulfonylurea herbicide use was discontinued on the farm. Resistant prickly lettuce plants were found at seven sites away from the original infested farm. Several sites were near the farm along roadsides that had been sprayed with sulfometuron. This study shows that the proportion of resistant prickly lettuce decreased where previously found, but its range increased.

Effect of weed interference duration and weed-free period on glufosinate-resistant rice was evaluated in 1998 and 1999. Weed interference for more than 2 wk reduced plant height 12 wk after emergence compared with the season-long weed-free treatment. Grain yield loss of 1,090 to 4,880 kg/ha was observed when weeds were allowed to interfere with rice from 2 wk to season-long. The weed-free period study indicated that early control of weeds could sustain rice growth and yield potential. This research suggests that effective weed control from 1 to 6 wk after rice emergence is important in fields with high weed densities for maximizing yield potential of glufosinate-resistant rice.

Post-application seasonal (May-July) average concentrations of atrazine, cyanazine, and, to a lesser extent, alachlor sometimes exceed their Maximum Contaminant Levels (MCLs) (3 ug/L for atrazine and 2 ug/L for alachlor) or Maximum Contaminant Level Goal (MCLG) (1 ug/L for cyanazine) in surface waters of the Mississippi and Great Lakes Basins. These three chemicals are among the primary pre-emergent herbicides applied to corn. MCLs and MCLGs are compared to annual average concentrations for regulatory purposes. However, annual average concentrations are much less frequently reported than post-application seasonal averages. In most cases, both seasonal and annual average concentrations are substantially less than the MCLs or MCLG. However, actual and estimated annual mean concentrations occasionally exceed the MCLs or MCLG. Actual or estimated exceedences occur more frequently for atrazine and cyanazine than for alachlor, and may occur more frequently in lakes or reservoirs with long retention times than in streams and rivers. Additional year round data, and data for lakes and reservoirs, are needed to determine the extent to which such exceedences occur throughout the corn belt. The American Water Works Association (AWWA) believes that substantial numbers of Community Water Systems (CWSs) within the corn belt are currently, or will be, in violation of the revised Safe Drinking Water Act (SDWA) with respect to atrazine and cyanazine. They are concerned that such violations could result in numerous CWSs having to implement expensive tertiary treatment systems such as granular activated carbon to decrease herbicide concentrations. The United States Environmental Protection Agency, (US EPA) is continuing to review data on the pesticide concentrations in reservoirs and lakes that registrants have been submitting over the last 18 mo under the 6(a)(2) adverse impact provision of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA). The US EPA is also currently using computer modeling and other methods to evaluate potential alternative and/or supplemental herbicides to reduce atrazine use. In June 1992, the US EPA approved revised labeling that is designed to reduce indirect atrazine loadings to surface waters. Additional mitigation methods have been proposed and are being considered.

Field dodder is a parasitic plant that attaches to the stems and leaves of broadleaf plants, including weeds, field crops, vegetables, and ornamentals, throughout most agricultural regions of the world. Effective field dodder control is extremely difficult to achieve, due to the nature of attachment and close association between host and parasite, which requires a highly effective and selective herbicide to destroy the parasite without crop damage. Previous studies have demonstrated the tolerance of certain tomato varieties to dodder parasitism. The aim of the present study was to evaluate the ability of sulfonylurea herbicides to control field dodder under greenhouse and field conditions. Two greenhouse studies and three field studies were conducted to evaluate the efficiency and crop selectivity of the sulfonylurea herbicides sulfosulfuron, rimsulfuron, halosulfuron, and flazasulfuron in controlling field dodder parasitizing tomato plants. Sulfosulfuron at 50 or 100 g ai ha−1 was effective and safe for tomato in field dodder control, while the other herbicides exhibited little or no dodder control.

Selective annual bluegrass (ABG) control with mesotrione is often inconsistent, and sequential applications might be required for complete control. The complementary nature of p-hydroxyphenylpyruvate dioxygenase (HPPD)- and photosystem II (PSII)-inhibiting herbicides is well documented. The HPPD-inhibiting herbicide mesotrione and the PSII-inhibiting herbicide amicarbazone both have efficacy against annual bluegrass and safety on certain cool-season turfgrasses. Topramezone is a HPPD-inhibiting herbicide being investigated for use in turfgrass. Field and greenhouse experiments were conducted to examine single applications of topramezone and mesotrione alone or in combination with amicarbazone for POST ABG control in spring. In greenhouse experiments, the combination of mesotrione (280 g ai ha−1) and amicarbazone (75 g ai ha−1) controlled ABG 70% by 21 d after treatment, > 29% more than either herbicide applied alone; these combinations were determined to be synergistic. Amicarbazone combined with topramezone (14.5 g ai ha−1) provided < 10% ABG control and was not synergistic. When combined with mesotrione, increasing amicarbazone rate to 150 or 255 g ha−1 did not increase ABG control compared to 75 g ha−1in field experiments. Combining mesotrione with amicarbazone resulted in a synergistic increase in POST ABG control at 1 and 2 wk after treatment (WAT). When applied alone or in combination with amicarbazone, increasing the mesotrione rate from 90 to 280 g ha−1 increased efficacy on ABG in field experiments. The combination of mesotrione at 280 g ha−1 and amicarbazone at 75 g ha−1 provided > 90% ABG control in field experiments. Future research should focus on sequential applications of mesotrione–amicarbazone combinations for ABG control in locations where ABG is historically more difficult to control.

Palmer amaranth is the most troublesome weed problem in mid-southern US crop production. Herbicides continue to be the most commonly employed method for managing Palmer amaranth, despite the weed’s widespread resistance to them. Therefore, farmers need research and extension efforts that promote the adoption of integrated weed management (IWM) techniques. Producers, crop consultants, educators, and researchers would be more likely to deploy diversified chemical and nonchemical weed management options if they are more informed about long-term biological and economic implications via user-friendly decision-support software. Described within is a recently developed software that demonstrates the effects of Palmer amaranth management practices on soil seedbank, risk of resistance evolution, and economics over a 10-year planning horizon. Aiding this objective is a point-and-click interface that provides feedback on resistance risk, yield potential, profitability, soil seedbank dynamics, and error checking of management options.

Field experiments were conducted to evaluate postemergence (POST)-applied tank mixtures of 560, 1,120, and 1,680 g ai/ha glyphosate with or without 1,120 g ai/ha SAN 582 (proposed name, dimethenamid) as burndown treatments or POST in glyphosate-tolerant soybean. SAN 582 was not antagonistic with glyphosate at the glyphosate rates evaluated. In the burndown study, glyphosate controlled horseweed 98% or more and curly dock 82% or more with or without SAN 582. However, broadleaf signalgrass emerged after the burndown treatments were applied. All tank mixtures that included SAN 582 controlled broadleaf signalgrass 84 to 96%, 6 wk after treatment. In the glyphosate-tolerant soybean study, glyphosate controlled barnyardgrass and johnsongrass present at the time of application 89% or more, regardless of rate. Tank mixtures of SAN 582 with glyphosate controlled late-season flushes of barnyardgrass through residual activity of the SAN 582. Applying SAN 582 with glyphosate improved soybean yield 500 kg/ha over glyphosate applied alone.

Bentgrass was used to bioassay oxyfluorfen in leaching experiments done in columns of soilless potting media and soils, with herbicide incorporated into the upper 2 to 4 cm. Depth of herbicide leaching increased in order in the following soils: peat and sand (1:1) mix, Stockton clay soil, Yolo fine sandy loam soil, and redwood bark and sand (3:1) mix. Depth of leaching was not related to soil organic matter content. Equilibration experiments showed that peat adsorbed 4 to 5 times more oxyfluorfen than redwood bark. Less leaching was observed in potting mixtures containing peat than bark. Raising the oxyfluorfen dose from 20 to 200 ppmw increased the depth of leaching and concentration of herbicide in the leachate, while a 10-fold increase in water volume had only a limited effect. Twenty ppmw of oxyfluorfen incorporated in the top of a peat-containing potting medium has a low risk of leaching out of the container.

Weeds are a major constraint in tomato production, especially in the absence of methyl bromide. Field trials were conducted in 2006 and 2007 to evaluate the integrated use of a mustard ‘Caliente’ (a blend of brown and white mustard) cover crop with one-half and full rate PRE/POST herbicides for weed control and crop response in polyethylene-mulched tomato. Caliente was flail mowed and incorporated into the soil prior to forming beds. PRE herbicides were applied under polyethylene mulch, and POST herbicides were sprayed over the top of tomato. Full rates for S-metolachlor, halosulfuron, and trifloxysulfuron were 1,600, 27, and 7.9 g ai/ha, respectively. Caliente had no effect on weed control or tomato injury and yield. Except for large crabgrass control and tomato injury and yield, only the main effect of herbicide selection and application rate affected these parameters. Tomato injury was minimal (< 6%) from PRE- and POST-applied herbicides. S-metolachlor applied PRE provided 66% purple nutsedge, 67% yellow nutsedge, and 77% Palmer amaranth control at 4 wk after transplanting (WATP). S-metolachlor–treated plots at the full rate produced the highest marketable fruit yield among herbicide treatments, with jumbo fruit yield equivalent to the hand-weeded treatment. Trifloxysulfuron was the best POST-applied herbicide based on marketable yield and weed control. POST-applied trifloxysulfuron provided 41% purple nutsedge, 58% yellow nutsedge, and 55% Palmer amaranth control at 8 to 9 WATP. Halosulfuron applied PRE controlled purple and yellow nutsedge 70 and 78%, respectively, at 4 WATP, and POST-applied halosulfuron controlled purple nutsedge 74% and yellow nutsedge 78% at 8 to 9 WATP. Halosulfuron applied either PRE or POST failed to control Palmer amaranth and large crabgrass. Greater weed control and marketable tomato yield were achieved with full rates of herbicides. This research demonstrates no additional advantage of Caliente mustard when used with herbicides in tomato. None of the PRE or POST herbicides applied alone were sufficient to maintain season-long, broad-spectrum weed control and optimum marketable yield in tomato. Therefore, integration of PRE and POST herbicides at full rates is suggested.

Understanding the biology of tropical soda apple (TSA) is necessary to develop effective control strategies. Tropical soda apple seedling emergence, growth, and regeneration from roots were evaluated. Plant growth (height, leaf number, flowering) was monitored over 110 d in a greenhouse experiment. Emerged seedlings required 83 d to reach a height of 40 cm and 108 d to flower. Total nonstructural carbohydrate concentrations in TSA root and stem fractions, monitored monthly for 1 yr, were highest in December (35%-root, 18%-stem). Seedling emergence as affected by planting depth (0, 1, 2, 4, 8 cm) and regeneration from root segments (7.5, 15 cm long) placed on the soil surface and 5 and 10 cm deep were studied in separate greenhouse experiments. Seedling emergence was lowest (P < 0.05) for seed placed on the soil surface (6.9%) and at a depth of 8 cm (19.4%) with the highest level of TSA emergence predicted at 63% for seed planted 3.6 cm deep. Regeneration from roots was higher (P < 0.05) for the 15-cm root segments than for the 7.5-cm segments while depth of root segment placement did not affect regeneration. Weed control strategies should involve cultural and chemical practices that affect both roots and seeds.

‘Lemberger’ wine grape response to fall application of selected herbicides applied at simulated drift rates was studied in 1992 and 1993. Chlorsulfuron, thifensulfuron, 2,4-D, glyphosate, bromoxynil, and 2,4-D plus glyphosate were applied at 1/100, 1/33, 1/10, and 1/3 of a selected maximum rate for use in wheat or fallow. All herbicides, except bromoxynil and thifensufluron, caused symptoms on grapevines at the highest rate during the spring following fall application. The most severe symptoms were caused by 2,4-D and 2,4-D plus glyphosate, whereas the least symptoms were caused by chlorsulfuron and glyphosate. The severity of symptoms increased and shoot growth, leaf area, internode length, and dry cane weight decreased as the rates of 2,4-D and 2,4-D plus glyphosate increased. Chlorsulfuron and glyphosate reduced the growth of grapevines only when applied at the highest rate during the fall. The data show that exposure of wine grapes to 2,4-D or 2,4-D plus glyphosate during the fall can adversely affect the growth of grapevines the following spring.

Two field experiments were conducted to evaluate the effects of selected herbicides on Italian ryegrass, combined Italian ryegrass plus wheat forage production, and returns from hard red winter wheat grain. Herbicides included BAY FOE 5043 + metribuzin (4:1 w/w premix), BAY MKH 6562, chlorsulfuron, chlorsulfuron + metsulfuron (5:1 w/w premix), diclofop, MON 37560, pendimethalin, ICIA 0604, and triasulfuron. Italian ryegrass was controlled 80% or more by 28 of 34 treatments. Grain dockage was reduced by 33 of 34 treatments at both sites, and grain yield was improved at both sites by 29 of 34 treatments. No herbicide treatment decreased forage protein content, but forage yield was frequently decreased by controlling Italian ryegrass. Gross returns from wheat grain were improved over the untreated check by all but six treatments at site 1, and by all but one treatment at site 2. The data did not support the hypothesis that returns from forage plus grain could be maximized by delaying Italian ryegrass control until grazing termination.

Open field production of fruit and nut-tree nursery stock depends upon preplant soil fumigation, extensive tillage, and hand-labor throughout the growing season for adequate weed control. Because methyl bromide, the favored fumigant, is being phased out because of environmental concerns and the costs of both fuel and labor continue to rise, herbicides are likely to become a more important weed management tool in the tree nursery industry. Two trials were conducted to evaluate weed control and crop safety with several herbicides applied following fumigation with methyl bromide or 1,3-dichloropropene in central California stone-fruit nurseries. PRE and POST-directed applications of several labeled and unlabeled materials were applied in a band over seeded peach rootstock or applied after emergence with a drop-nozzle spray boom. Crop productivity and weed control were monitored throughout the 1-yr growing season. PRE oryzalin and dithiopyr treatments provided the best weed control with very little crop injury. PRE applications of flumioxazin, rimsulfuron, and sulfentrazone did not have adequate crop safety at the rates and timings tested. However, POST-directed applications of flumioxazin and rimsulfuron were much safer to the peach and almond crops and should be evaluated in future trials. Additional herbicides and application techniques are needed to find acceptable, safe control measures for weeds, such as California burclover, common mallow, and redstem filaree, which often are poorly controlled with preplant fumigation in tree nurseries.

Full-season johnsongrass competition reduced sugar yields by 53 and 44% in ‘CP 70–321’ and ‘CP 72–370’ sugarcane, respectively, primarily by reducing sugarcane stalk populations. Stalk population and height and sugar yields of both cultivars were optimized when asulam was applied at 3.7 kg ai/ha during April and early May. Asulam at 3.4 kg/ha, applied a second time 8 weeks later, generally increased johnsongrass control but did not increase sugar yields over one early application. By delaying the application, the potential for sugarcane injury from asulam applied once or twice increased in both cultivars. Injury appeared to be related to the stage of sugarcane growth and temperature and moisture stress at application time with asulam phytotoxicity being more pronounced in CP 72–370. Populations of johnsongrass stems in the year after treatment reflected the degree of johnsongrass control by asulam and the competitiveness of the crop in the previous year.

Field trials were conducted in 2000 and 2001 in New Jersey to evaluate quinclorac and siduron for large crabgrass control in summer-seeded creeping bentgrass (‘L-93’). Bentgrass was surface seeded on June 30 and June 26 in 2000 and 2001, respectively. Treatments consisted of preemergence (PRE) applications of siduron at 3.4, 5.0, and 6.7 kg ai/ha and PRE and postemergence (POST) applications of quinclorac at 0.4, 0.6, 0.8, and 1.7 kg ai/ha. POST applications were timed to a crabgrass growth stage of three leaves to one tiller. All POST quinclorac applications included methylated seed oil at 1% (v/v). Percent crabgrass cover in untreated plots at 30 d after planting (DAP) averaged 10 and 50% in 2000 and 2001, respectively. All PRE treatments, with the exception of quinclorac applied at 0.4 kg/ha in 2001, reduced crabgrass cover by 80% or more at 30 DAP. Crabgrass control decreased in late August when siduron and quinclorac were applied at the lower rates in 2001. PRE quinclorac applications at the rate of 0.6 kg/ha or higher in 2000 or 1.7 kg/ha in 2001 caused significant thinning of the bentgrass stand at 30 DAP. All POST quinclorac treatments provided excellent crabgrass control in 2000, but the 0.8-kg/ha or higher rate was required to reduce crabgrass infestation levels by at least 80% in 2001. All POST quinclorac applications caused significant chlorosis to the creeping bentgrass in both years. However, significant thinning of the bentgrass stand was not evident, with the exception of 1.7 kg/ha, in 2001. These studies suggest that PRE applications of siduron should be used for the highest level of creeping bentgrass safety in summer restoration projects. The use of quinclorac should be limited to POST applications to control escaped crabgrass once the newly emerging creeping bentgrass has become well established.

Fatoua villosa (mulberry weed) is a new and invasive weed of container nurseries and landscapes in the southeastern United States. Studies were conducted to determine the effects of light, planting depth, mulch depth, and temperature on mulberry weed seed germination and seedling emergence. Light stimulated mulberry weed seed germination, with less than 5% of seeds germinating in the dark compared with 48 to 60% germinating in the light. In all emergence studies, the highest number of seedlings emerged when seeds were placed on the soil surface, with emergence decreasing as planting or mulch depth increased. Planting depths of ≥ 1.8 cm or mulch depths of ≥ 3.7 cm reduced mulberry weed emergence by ≥ 90%. These data suggest that mulch would control mulberry weed effectively. To study the effects of temperature on germination, two seed batches collected locally in October 1998 and August 1999 were used. Maximum germination of seeds collected in 1998 occurred at 25 C, with germination decreasing at higher temperatures and no germination at lower than 15 C or over 40 C. For seeds collected in 1999, maximum germination occurred from 19 to 29 C, with germination decreasing with temperatures above 29 C or below 19 C. At temperatures of 15 and 42 C germination, percentages were 71 and 11%, respectively. Seedlings germinated at 15 C developed slowly but otherwise appeared normal. For both seed lots, seedlings were stunted and chlorotic at ≥ 38 C. That mulberry weed seed germinated over a wide range of temperatures suggests its potential to emerge throughout most of spring, summer, and autumn in the southeastern United States.