This study measured weed interference in soybean and corn as affected by residue management tactics following a sequence of oat and winter wheat. Residue management tactics compared were conventional tillage, no-till, and no-till plus cover crops. Treatments were split into weed-free and weed-infested conditions; prominent weeds were green and yellow foxtail and common lambsquarters. Grain yield of soybean did not differ between weed-free and weed-infested conditions with no-till, whereas weeds reduced yield 25% in the tilled system. Corn responded inconsistently to treatments, with more than 40% yield loss due to weed interference in 1 yr with all treatments. Cover crops did not improve weed management compared with no-till in either crop. Seedling emergence of the weed community differed between tillage and no-till; density of weed seedlings was fivefold higher with tillage, whereas seedling emergence was delayed in no-till. The initial flush of seedlings occurred 2 to 3 wk later in no-till compared with the tilled system. Designing rotations to include cool-season crops in a no-till system may eliminate the need for herbicides in soybean to manage weeds.

Dogfennel is one of the most problematic weeds in Florida pasturelands and its control can become inconsistent as the plant matures. A premix of triclopyr + fluroxypyr has been recently introduced for weed control in pastures and rangeland; however, little published information exists concerning the control of dogfennel in pastures with this herbicide combination. Therefore, experiments were initiated to determine the efficacy of triclopyr + fluroxypyr compared with commonly used pasture herbicides on dogfennel at three heights. All herbicides utilized in this study are commonly used for dogfennel control. Dogfennel control was affected by both herbicide treatment and dogfennel height. In general, 0.80 + 0.28 kg ai/ha of 2,4-D amine + dicamba resulted in inconsistent control, especially as dogfennel plants increased in size. Increasing the rate of 2,4-D amine + dicamba to 1.21 + 0.42 kg/ha increased the consistency. Triclopyr + fluroxypyr provided similar levels of control as that of 1.21 + 0.42 kg/ha 2,4-D amine + dicamba. In all locations, control of 154-cm dogfennel was signficanatly lower than that of 38-cm dogfennel. These data indicate that triclopyr + fluroxypyr is an effective option for dogfennel control, but dogfennel height at the time of application is an important factor for optimizing control.

Dodder is a serious parasitic weed in the crops in which it is a problem (particularly citrus). Alternaria destruens is the active ingredient in a registered bioherbicide for control of dodder species. In greenhouse studies, the treatments applied to citrus parasitized with field dodder were a nontreated control; oil at 7.5% v/v in water; ammonium sulfate at 0.125% w/v in water; glyphosate at 0.02 kg ae/L; A. destruens at 1.8 × 1010 spores/L; A. destruens (1.8 × 1010 spores/L) + oil at 7.5% v/v in water; and a mixture of A. destruens (1.8 × 1010 spores/L) + oil at 7.5% v/v in water + glyphosate at 0.02 kg ae/L + ammonium sulfate 0.125% w/v (the mixture treatment). The highest disease or damage severity rating out of all treatments, measured as the area under the disease or damage progress curve (AUDPC), was obtained for the mixture treatment. By 35 d after treatment, all field dodder plants that received the mixture treatment were dead but the host plant, citrus, was not. These results indicate the feasibility of integrating glyphosate, ammonium sulfate, and A. destruens to manage dodder.

Mesotrione, a carotenoid biosynthesis inhibitor, is being evaluated for use in turfgrass systems. It was hypothesized that root absorption of soil-applied mesotrione is necessary for effective weed control. Greenhouse studies were conducted to compare the effects of foliar-, soil-, and soil-plus-foliar–applied mesotrione at 0.14 and 0.28 kg ai/ha on yellow nutsedge and large crabgrass. In general, greatest control of yellow nutsedge and large crabgrass was by treatments that included soil application. In addition, mesotrione applied at 0.28 kg/ha generally controlled both yellow nutsedge and large crabgrass more effectively than mesotrione applied at 0.14 kg/ha. Soil- and soil-plus-foliar–applied mesotrione at 0.28 kg/ha controlled yellow nutsedge more than foliar-applied mesotrione 56 d after treatment. Soil-plus-foliar–applied mesotrione at 0.28 kg/ha controlled large crabgrass more than any other treatment 28 d after treatment. Soil- and soil-plus-foliar–applied mesotrione at both rates reduced large crabgrass foliar dry weight more effectively than did foliar-applied mesotrione. Results indicate that root absorption of mesotrione from soil is beneficial for the effective control of both yellow nutsedge and large crabgrass. For this reason, methods such as granular or high-volume applications, which enhance delivery of mesotrione to soil, would be potentially beneficial for turfgrass weed control.

Sourgrass is a stoloniferous perennial grassy weed found on golf courses throughout Hawaii. No herbicides are currently labeled for selective control of sourgrass in seashore paspalum turf, a species used regularly on golf courses throughout the tropics. A single granular application of fine salt (99% sodium chloride, 1% sodium silicoaluminate, 83% of particles 0.5 to 0.25 mm in diameter) at a rate of 1,464 kg/ha provided 84 and 23% control of sourgrass 6 wk after initial treatment (WAIT) in 2007 and 2008, respectively. Sequential granular applications of fine salt at 488 kg/ha provided 92 and 96% control of sourgrass in 2007 and 2008, respectively, at 6 WAIT. Granular applications of a coarse salt (100% sodium chloride, 75% of particles 2.0 to 1.0 mm in diameter) provided a lower level of control than fine salt at both the 1,464- and 488-kg/ha rates on three out of four rating dates in 2008; a similar trend was observed in 2007, but no significant differences were observed between these treatments. All salt treatments led to higher soil sodium adsorption ratios (SAR) and electrical conductivity (ECe) than the untreated check; however, levels reported in this study were significantly lower than the threshold SAR and ECe levels that have been associated with reduced seashore paspalum growth. Sequential applications of MSMA at 1.12 kg/ha and MSMA plus metribuzin at 1.12 kg/ha and 0.28 kg/ha, respectively, provided greater than 90% control in 2008, but less than 40% control in 2007. Greater seashore paspalum injury was observed following applications of MSMA and MSMA plus metribuzin than following salt applications. Additional research is needed to evaluate strategies for controlling sourgrass in seashore paspalum turf that do not induce phytotoxic injury after application.

Centipedegrass is tolerant of both atrazine and mesotrione when applied separately to established turf. However, no information is available regarding the use of mesotrione or the synergistic mixture of atrazine plus mesotrione applied to centipedegrass during seeded establishment. Research was conducted to evaluate centipedegrass tolerance to various rates and combinations of atrazine plus mesotrione when applied 14 d after emergence (DAE). Experiment 1 evaluated centipedegrass tolerance to atrazine and mesotrione in a broad rate-range screen in a greenhouse environment. Variations were observed between greenhouse trial runs with respect to injury and biomass with less injury and decrease in biomass observed in run 2. Overall, atrazine alone and atrazine plus mesotrione were more injurious for a greater time period and decreased biomass more than mesotrione alone. In fact, although mesotrione alone initially reduced centipedegrass photosystem II efficiency, an overall increase in efficiency was observed 28 d after treatment (DAT). Based on experiment 1, atrazine at 0.28 kg ai/ha was the maximum rate that could be applied to seedling centipedegrass when tank mixed with mesotrione. Experiment 2 evaluated atrazine at 0.28 kg/ha plus mesotrione at 0.03 to 0.28 kg/ha on centipedegrass field establishment. Although all atrazine plus mesotrione treatments reduced centipedegrass ground cover 28 DAT; no treatment reduced centipedegrass ground cover 49 DAT.

Canada thistle is a perennial spreading weed that is difficult to control in farming systems with reduced reliance upon herbicides for weed management. Experiments were conducted from 2006 to 2008 at Champaign, IL, to evaluate the combined effects of summer annual cover crops and mowing on Canada thistle growth and survival. Whole plot treatments were fallow, buckwheat, sudangrass–cowpea mixture (MIX), and sudangrass. The subplot treatments were mowing frequencies (0 to 2 times). Cover crop and mowing did not interact to suppress Canada thistle. MIX and sudangrass produced more standing biomass, greater regrowth, and more surface mulch following mowing than the buckwheat. A single season with sudangrass or MIX reduced Canada thistle shoot density and mass to less than 20% of the initial values through two growing seasons. Mowing alone only suppressed Canada thistle shoot density and mass on the site with greater initial density. A sudangrass or MIX cover crop alone or combined with mowing suppresses Canada thistle, but intensive management must continue for several years to eliminate patches.

Mesosulfuron is often applied to wheat at a time of year when top-dress nitrogen is also applied. Current labeling for mesosulfuron cautions against applying nitrogen within 14 d of herbicide application. Soft red winter wheat response to mesosulfuron and urea ammonium nitrate (UAN) applied sequentially and in mixtures was determined at three locations in North Carolina and Georgia during 2005 and 2006. Mesosulfuron at 0, 15, and 30 g ai/ha was applied in water to wheat at Feekes growth stage (GS) 3 followed by UAN at 280 L/ha 2 h, 7 d, 14 d, and 21 d after mesosulfuron. Mesosulfuron applied in UAN was also evaluated in 2006. Mesosulfuron injured wheat 6 to 9% in 2005 and 12 to 23% in 2006 when UAN was applied 2 h or 7 d after the herbicide. Wheat injury did not exceed 8% when UAN was applied 14 or 21 d after the herbicide. Greatest injury, 35 to 40%, was noted when mesosulfuron and UAN were combined. Wheat yield was unaffected by mesosulfuron or time of UAN application in 2005. In 2006, yield was affected by the timing of UAN application relative to mesosulfuron; wheat yield increased as the interval, in days, between UAN and herbicide applications increased. To avoid crop injury and possible yield reduction, mesosulfuron and UAN applications should be separated by at least 7 to 14 d. These findings are consistent with precautions on the mesosulfuron label.

Field research was conducted to evaluate the effectiveness of herbicides and carrot mowing for swamp dodder control. Herbicide evaluation indicated the highest carrot yield and lowest crop injury with pendimethalin compared to the industry standard linuron. Swamp dodder control with pendimethalin was greater than 80% at 56 and 70 d after planting (DAP). Other herbicides controlled swamp dodder, but crop injury was unacceptable. Carrot yield was greater where pendimethalin or s-metolachlor was applied compared to all other herbicides. Carrot mowing once 72, 86, or 100 DAP and mowing twice (72 plus 100 DAP) reduced the percentage of carrots infected with swamp dodder. Carrot infection level was least when mowed 100 DAP, and mowing did not increase yield compared to the non-treated check. These results suggest that the integration of pendimethalin for early-season swamp dodder control, followed by mowing 100 DAP, could reduce the impact of swamp dodder on carrots.

Dry edible bean class and cultivar response to dimethenamid and metolachlor was investigated in the greenhouse and field. Kidney and cranberry cultivars, as well as a small red cultivar, were not injured by dimethenamid applied PRE at 2,100 g ai/ha in the greenhouse, whereas pinto bean tolerance varied and navy and black bean cultivars were injured by this rate. Injury to navy bean was greater in the greenhouse when dimethenamid and metolachlor were placed in the zone above and including the seed, compared with placement in the seed, root, or root plus seed zone. In an application timing field study, dimethenamid at 1,300 g/ha applied at the crook or unifoliate growth stage caused injury to navy bean, delayed maturity, and reduced seed yield. Metolachlor at 1,400 g ai/ha delayed maturity when applied at the unifoliate growth stage but did not reduce seed yield. Dimethenamid or metolachlor PRE, at 1,300 or 2,800 g ai/ha, respectively, injured navy and black bean cultivars, but seed yield was not reduced in a cultivar tolerance field study. In a planting date study, dimethenamid PRE at 2,300 g/ha reduced leaf area and delayed maturity compared with the nontreated control when pooled over five planting dates and cultivars in each of 2 yr. Metolachlor PRE at 2,800 g/ha reduced leaf area in 1 yr and delayed maturity in both years when pooled over planting dates and cultivars. If weed control and herbicide costs are comparable, metolachlor at a standard use rate is a safer choice than dimethenamid for use in navy and black bean production.

Improving crop vigor can suppress growth of weeds present in the crop. This study examined the impact of preceding crop and cultural practices on rye growth in winter wheat. Preceding crops were soybean, spring wheat, and an oat/dry pea mixture. Two cultural treatments in winter wheat were also compared, referred to as conventional and competitive canopies. The competitive canopy differed from the conventional in that the seeding rate was 67% higher and starter fertilizer was banded with the seed. The study was conducted at Brookings, SD. Rye seed and biomass production differed fourfold among treatments, with winter wheat following oat/pea being most suppressive of rye growth. Rye produced 63 seeds/plant in winter wheat with a competitive canopy that followed oat/pea, contrasting with 273 seeds/plant in conventional winter wheat following spring wheat. Yield loss in winter wheat due to rye interference increased with rye biomass, but winter wheat was more tolerant of rye interference following oat/pea compared with the other preceding crops. Regression analysis indicated that winter wheat yield loss at the same rye biomass was threefold higher following spring wheat or soybean compared with oat/pea as a preceding crop. Winter wheat competitiveness and tolerance to rye can be improved by increasing the seeding rate, using a starter fertilizer, and growing winter wheat after an oat/pea mixture.

A field trial was conducted for 3 yr (2005 through 2007) near Scottsbluff, NE, to examine weed control, crop safety, forage production, and economics of glyphosate-tolerant and conventional alfalfa establishment systems. Glyphosate applied to alfalfa at the unifoliate growth stage provided 67% weed control and was similar to imazamox applied at the two-trifoliate leaf stage. Delaying glyphosate application until alfalfa had reached the two-trifoliate growth stage improved weed control to 83%, and weed control was similar to imazamox plus 2,4-DB and imazethapyr plus 2,4-DB. Imazamox and imazethapyr caused minor crop injury, and the addition of bromoxynil or 2,4-DB to both herbicides further decreased crop safety. Weeds were most competitive with the first forage harvest and reduced relative feed value, crude protein, and value (dollars per t) of forage compared to forage that had been treated with herbicides. The total forage yield for the season consisted of three forage harvests and was greatest when no herbicides were applied. The total forage yield of plots treated with glyphosate at the two-trifoliate growth stage was greater than that of plots treated with imazamox or imazethapyr in combination with bromoxynil. When glyphosate was applied at the two-trifoliate growth stage, seasonal forage yield was similar to forage treated with imazamox, imazethapyr, or both herbicides in combination with 2,4-DB. When herbicide was applied to alfalfa at the two-trifoliate growth stage, the net return from using glyphosate with a glyphosate-tolerant alfalfa variety or utilizing imazamox with a conventional alfalfa variety were similar at $742 and $743/ha, respectively.

Field trials were conducted to determine if tillage and soil-applied herbicides had an effect on weed control and sugarbeet growth with a micro-rate herbicide program. Sugarbeet emergence was earlier in the moldboard plowed system compared with the chisel plowed system at three of four sites. Conditions were dry and sugarbeets emerged 5 d later in the moldboard plowed system compared with the chisel plowed system at the fourth site. Even though the rate of sugarbeet emergence differed between tillage systems at all four sites, final sugarbeet populations did not differ at two of the four sites. Sugarbeet injury from PRE treatments of S-metolachlor, ethofumesate, and ethofumesate plus pyrazon, followed by four POST micro-rate applications, ranged from 11 to 27% and 1 to 18% in the chisel and moldboard plowed systems, respectively, 6 wk after planting (WAP). Under wet conditions, sugarbeet stand was reduced and injury was greatest from PRE applications of S-metolachlor. Common lambsquarters, pigweed (redroot pigweed and Powell amaranth), and giant foxtail control in mid-August was consistently higher when a PRE herbicide was applied prior to micro-rate herbicide treatments. Even though there were differences between PRE and no-PRE treatments with respect to sugarbeet injury and weed control, recoverable white sucrose yield did not differ between herbicide treatments. However, recoverable white sucrose yield was greater in the moldboard plowed treatments compared with the chisel plowed treatments at three out of the four sites.

Field experiments were carried out during two growing seasons at Adnan Menderes University, Faculty of Agriculture, in Aydın-Turkey to evaluate the weed control efficacy of olive processing waste (OPW) in okra, faba bean, and onion. OPW was incorporated into the soil prior to seeding at 10, 20, 30, and 40 tons (t)/ha. Non-treated plots and plots treated with trifluralin in okra and pendimethalin in faba bean and onion were used for comparison. OPW suppressed common purslane, redroot pigweed, and junglerice in okra; littleseed canarygrass, annual bluegrass, wild chamomile, and shepherd's-purse in faba bean and onion. OPW was in most cases equally as effective as soil herbicides; however, 10 t/ha provided sometimes lower efficacy than herbicides. OPW had no negative effects on okra and faba bean, while onion was negatively affected by doses over 30 t/ha. Overall, OPW can be applied at 10 to 20 t/ha doses for weed control with adequate crop safety.

Field studies were conducted from 2004 to 2006 to evaluate the tolerance of three annual medic species (bur, black, and barrel medic) to selected POST herbicides. 2,4-DB at 0.56 and 1.12 kg/ha caused the most stunting across all three species. Imazethapyr at 0.1 kg/ha stunted all three annual medics in 1 of 3 yr whereas flumetsulam at 0.04 kg/ha stunted black and barrel medics in 1 of 3 yr. Clethodim at 0.28 kg/ha did not cause any medic stunting. Imazethapyr, imazamox, and 2,4-DB at 0.56 kg/ha reduced henbit dry matter composition compared to the untreated check whereas clethodim, flumetsulam, and 2,4-DB at 1.12 kg/ha did not. In 2004, 2,4-DB at 1.12 kg/ha reduced dry weight yield of bur and barrel medic but not black medic when compared with the untreated check. Black medic treated with imazethapyr at 0.05 and 0.1 kg/ha and clethodim at 0.28 kg/ha produced higher dry weight yield than the untreated check. In 2006, both rates of 2,4-DB and flumetsulam at 0.04 kg/ha reduced dry weight yield of bur medic compared to the untreated check. Barrel medic dry weight yields were reduced by both rates of 2,4-DB and flumetsulam compared to untreated check. No herbicides reduced dry weight yields of black medic.

Organic vegetable producers have limited options for managing weeds. They cite weed management as their number one research priority. Studies were conducted in 2004 and 2005 at the Black Sea Agricultural Research Institute, Samsun, Turkey, to determine the weed suppressive effects of summer cover crops in organic kale production. Treatments consisted of grain sorghum, sudangrass, hairy vetch, grain amaranth, pea, and fallow. Weed density and total weed dry biomass were assessed before and at 14, 28, and 56 d after incorporation (DAI) of the cover crops. Kale was transplanted 14 DAI and hand weeded once after last weed evaluation (56 DAI). All cover crops produced at least 1 ton/ha (t/ha) biomass; grain sorghum produced more dry matter than all other cover crops in both years. After incorporation of the cover crops, hairy vetch and sorghum treatments showed fewer species, lower weed density, and total weed dry biomass compared with other treatments. Cover crops suppressed emergence of common purslane, common lambsquarters, redroot pigweed, European heliotrope, field pennycress, annual sowthistle, black nightshade, shepherd's-purse, wild mustard, sun spurge, Persian speedwell, annual mercury, and jimsonweed up to 56 DAI. Total kale yield in hairy vetch treatments was more than double that of the no cover crop, and was significantly higher than yield from the other cover crop treatments. These results indicate that hairy vetch, grain sorghum, and sudangrass have ability to suppress early-season weeds in organic kale production.

Field experiments were conducted to determine the critical period of weed interference in glyphosate- and glufosinate-resistant sugar beet, and to determine if PRE herbicides increased weed control or sugar beet root yield when glufosinate, glyphosate, or conventional POST herbicides were applied. Glyphosate- and glufosinate-resistant sugar beet root yields were reduced by up to 66 and 67%, respectively, when weeds remained all season in the weedy control treatment compared with yields when weed removal occurred as soon as the weeds were 2.5 cm tall, approximately 2 to 3 wk after planting (WAP). A critical period of weed interference did not occur in this research. The critical time of weed removal was approximately 8 WAP in 1998 and beyond 11 WAP in 1999. Weeds averaged 20 cm in height at 8 WAP and weed densities were greater in 1998 compared with 1999. The critical weed-free period for glyphosate- and glufosinate-resistant sugar beet was 4.5 to 5 WAP in 1998. In 1999, the critical weed-free period at the Michigan Sugar location was 1.5 WAP in glyphosate-resistant sugar beet, and 6.5 WAP in glufosinate-resistant sugar beet for the Michigan Sugar site. Glyphosate or glufosinate POST provided better weed control and resulted in greater sugar beet root yield compared with conventional POST herbicides when data were combined over PRE herbicide treatments. PRE herbicides improved the control of common lambsquarters and Amaranthus species in some of the site-years when data were combined over POST treatments, but sugar beet yield did not increase. Our research suggests that PRE herbicides will not be necessary in glyphosate- or glufosinate-resistant sugar beet. To avoid sugar beet yield loss, multiple POST applications of glyphosate or glufosinate will be needed until 6 to 9 WAP to prohibit yield loss from weeds emerging after the last POST application.

Cotton gins in Arkansas, western Tennessee, and western Mississippi were sampled for weed seed contamination of gin trash in fall 2007. A total of 473 samples were collected, with 453 samples from Arkansas. The objectives of this research were to determine the weed species most frequently found in gin trash and determine what means gin operators are using to dispose of gin trash. There were 25 weed species found in the gin trash samples—11 grass and 14 broadleaf weeds. Grass and broadleaf weeds were present in 41.4 and 8.5% of the samples, respectively. The most frequently found species were large crabgrass (19.0%), barnyardgrass (14.0%), goosegrass (12.9%), red sprangletop (8.2%) and Palmer amaranth (4.2%). Viable seeds of barnyardgrass, large crabgrass, Palmer amaranth, and prickly sida were present in the surface layer (0- to 25-cm depth) of gin trash piles after 1 yr of composting. Viable Palmer amaranth seeds were present in the surface layer of gin trash piles after 2 yr of composting, but no germinable seeds were found deeper than 25 cm following 1 yr of composting. Gin trash disposal involved application of the material to crop fields during the fall or winter months; composting followed by application of the compost as mulch or a soil amendment to gardens, flower beds, or crop fields; use as cattle feed; and coverage for landfills to reduce erosion and encourage growth of vegetation. Because of the demonstrated potential for weed seed dispersal via gin trash, including composted material, development of technologies to ensure disposal of a gin-trash product free of viable weed seed are justified.

The effects of flumioxazin in irrigation water were evaluated on four row crop species (corn, cotton, soybean, and wheat) and three ornamental species (begonia, impatiens, and snapdragon). Plants were overhead irrigated one time with flumioxazin at concentrations of 0, 10, 25, 50, 100, 200, 400, 800, 1,600, and 3,200 µg ai/L in water equivalent to 1.27 cm. Ornamental plant tolerances on the basis of a 10% reduction in dry weight (effective concentration 10 [EC10]) were as follows: impatiens (40) < begonia (103) < snapdragon (7,024). The EC10 values of flumioxazin on the basis of dry weight values for row crop species were wheat (35) < corn experiment 1 (53) < cotton (106) < corn experiment 2 (181) < soybean (193). EC10 values for plant height were similar to values for plant dry weight for ornamental and crop species. Snapdragon was the only plant evaluated that was mature at the time of treatment; consequently, all other species were moderately to highly sensitive to irrigation water containing flumioxazin. These data show that flumioxazin can injure and kill immature ornamental and crop species within the potential maximum concentration of 400 µg/L; however, the very short half-life of this herbicide in water with pH 7.0 to 9.0 (ca. 16 h to 17 min) could result in less injury than suggested in this study.

Herbicide applications prior to turf renovation often fail to provide complete control of perennial warm-season turfgrass species like seashore paspalum. Surface applications of dazomet at 506 kg/ha provided > 90% POST control of ‘SeaDwarf’ seashore paspalum turf in 2008. Although applications of glyphosate at 5.6 kg/ha or fluazifop-P-butyl at 0.42 kg/ha induced significant injury, these treatments provided < 40% POST control of SeaDwarf seashore paspalum turf 10 wk after initial treatment (WAIT) in 2008. A similar response was noted following applications of glyphosate plus fluazifop-P-butyl at rates of 5.6 kg/ha and 0.42 kg/ha, respectively. POST control following applications of glyphosate at 5.6 kg/ha plus fluazifop-P-butyl at 0.42 kg/ha, prior to applying dazomet at 506 kg/ha, was not different from that which was observed following applications of dazomet alone at 506 kg/ha. These data suggest that granular applications of dazomet alone, at 506 kg/ha, can be used to provide effective control of SeaDwarf seashore paspalum prior to renovation.