Methyl bromide (MBr) was widely used as a soil fumigant to manage pests in the planting bed prior to transplanting fresh market tomato; however, it has been banned by the United Nations Environment Programme. Alternatives to MBr must be implemented to sustain productivity in fresh market tomato. Dimethyl disulfide plus chloropicrin (DMDS : Pic) is a fumigant alternative to methyl bromide for the management of yellow nutsedge and other soil-borne pests in tomato. Fumigant costs, environmental concerns, and risk mitigation measures encourage reduced fumigant application rates. Virtually impermeable film (VIF) and totally impermeable film (TIF) provide greater fumigant retention than low density and high density polyethylene film, VIF and TIF can allow for reduced fumigant application rates while maintaining fumigant efficacy. The objectives of this research were to evaluate TIF with reduced rates of shank-applied DMDS : Pic (79 : 21 w/w) for the control of yellow nutsedge in tomato. Treatments included a standard rate of DMDS : Pic (468 L ha−1) under VIF and TIF, a high rate (561 L ha−1) under VIF, three reduced rates (187 L ha−1, 281 L ha−1, and 374 L ha−1) under TIF, and a nontreated control under TIF and VIF. Results indicated rates may be reduced from a standard 468 L ha−1 under VIF to 187 L ha−1 (67% reduction) under TIF while maintaining yellow nutsedge control and tomato yields. In addition, the results indicated that nontreated TIF managed yellow nutsedge better than nontreated VIF because of decreased penetration of the mulch by yellow nutsedge.

Field studies were conducted to determine if varying the time N fertilizer was applied would affect downy brome interference in winter wheat. Five treatments were compared: four broadcast application times of NH4NO3 at 56 kg N ha-1 during the fallow-crop cycle: 1) during fallow; 2) at planting; 3) during crop dormancy; 4) before winter wheat jointing; and 5) a control where no N was applied. Downy brome was least responsive to N applied during fallow. All N applications during the growing season of winter wheat increased downy brome biomass and culms m-2. Downy brome interference prevented winter wheat from responding positively to N. For example, when crop season precipitation was only 70% of normal, applying N reduced grain yield of winter wheat infested with downy brome from 12 to 28%. This study indicates that N manipulation offers potential for reducing downy brome interference in winter wheat.

Saflufenacil is a new herbicide being developed for preplant burndown and PRE broadleaf weed control in field crops, including corn, soybean, sorghum, and wheat. Field experiments were conducted in 2006 and 2007 at Concord, in northeast Nebraska, with the objective to describe dose–response curves of saflufenacil applied with several adjuvants for broadleaf weed control. Dose–response curves based on log-logistic model were used to determine the effective dose that provides 90% weed control (ED90) values for six broadleaf weeds (field bindweed, prickly lettuce, henbit, shepherd's-purse, dandelion, and field pennycress). Addition of adjuvants greatly improved efficacy of saflufenacil. For example, the ED90 values for field bindweed control at 28 d after treatment were 71, 20, 11, and 7 g/ha for saflufenacil applied alone, or with nonionic surfactant (NIS), crop oil concentrate (COC), or methylated seed oil (MSO), respectively. MSO was the adjuvant that provided the greatest enhancement of saflufenacil across all species tested. COC was the second-best adjuvant and provided control similar to MSO on many weed species. NIS provided the least enhancement of saflufenacil. These results are very similar to the proposed label dose of saflufenacil for burndown weed control, which will range from 25 to 100 g/ha with MSO or COC. We believe that such a dose would provide excellent burndown control of most broadleaf weed species that emerge in the fall in Nebraska.

Influences of a hairy vetch cover crop and residual herbicides were examined in field corn in 1991 and 1992. Hairy vetch was seeded in mid-August and killed the following May with tillage, mowing, or glyphosate plus 2,4-D (no-till). These cover crop management systems were compared with a no-cover treatment. Residual herbicides including atrazine plus metolachlor applied PRE at three rates and nicosulfuron plus thifensulfuron applied POST at a single rate were compared within cover crop management systems. All cover crop management systems effectively controlled hairy vetch except mowing in 1992. The corn population was reduced in mow treatments containing uncontrolled vetch. Hairy vetch mulch suppressed some weeds in the no-till treatments in 1991, but more annual grass was noted late in the season with no-till into hairy vetch than with the no-cover treatments in 1992. Residual herbicide performance was similar across cover crop management systems, except for fall panicum control which decreased in some no-till systems. Unlike soil-applied herbicides, performance of POST herbicides was unaffected by cover crop management systems.

Field trials were conducted in 1999 and 2000 to determine the influence of weed size and the number of glyphosate or glufosinate applications on weed control and sugarbeet yield. Glyphosate at 840 g/ha or glufosinate at 390 g/ha was applied one, two, or three times, beginning when the average weed height was 3, 10, 15, or 25 cm. Two sequential applications of glyphosate applied to 10-cm weeds or three sequential applications of glufosinate applied to 3-cm weeds provided weed control comparable to three sequential applications of desmedipham plus phenmedipham plus triflusulfuron plus clopyralid. Weed control and sugarbeet root yield were optimal for two postemergence applications of glyphosate and for three applications of glufosinate. Glyphosate provided greater control of redroot pigweed and common lambsquarters than glufosinate. Sugarbeet sucrose yield with both glyphosate and glufosinate weed control programs was nearly 10,000 kg/ha. Compared with two sequential applications of glyphosate, sucrose yield of glyphosate-resistant sugarbeet was reduced 15% by three sequential applications of desmedipham plus phenmedipham plus triflusulfuron plus clopyralid. Sucrose yields were similar between three sequential applications of glufosinate and three applications of desmedipham plus phenmedipham plus triflusulfuron plus clopyralid.

Alternative methods are needed to control weeds in no-till corn and soybean which minimize herbicide contamination of surface or ground water. The objective of this research was to determine whether between-row (BR) mowing + band-applied herbicide could help reduce herbicide use, without sacrificing summer annual weed control or yield, in no-till soybean and field corn. Glyphosate was applied shortly before or at planting to control emerged winter annual weeds in all treatments. In the BR mowing weed management system, the band-applied soil residual herbicides imazaquin + alachlor in soybean or atrazine + alachlor in corn were applied shortly before or after planting followed by two or more between-row mowings to control summer annual weeds. Annual weeds were first mowed when they were about 8 cm tall and again just before crop canopy closure. Between-row mowing weeds very close to the soil surface two or three times killed or suppressed summer annual grass and broadleaf weeds, chiefly giant foxtail, common cocklebur, and horseweed, when timed properly. The BR mowing weed management system increased yield above a weedy check in these no-till crops. It also controlled weeds and yielded as well as or better than broadcast-applied herbicide at the same rates. Use of soil residual herbicides to control summer annual weeds was reduced 50% by banding because only 50% of the field area was sprayed.

There is little information on the sensitivity of dry beans to flumioxazin. Tolerance of eight cultivars of dry beans representing four market classes (black, cranberry, kidney, and white beans) to preplant incorporated (PPI) and preemergence (PRE) applications of flumioxazin at the rate of 52.5, 70, and 140 g ai/ha were studied in three field experiments in Ontario in 2002 and 2003. There were no differences (P < 0.05) between two cultivars within a market class in their responses to flumioxazin. However, the four market classes differed in their responses to flumioxazin. Black and white beans were more sensitive to the PRE application of flumioxazin than cranberry and kidney beans. Flumioxazin applied PRE at 140 g/ha caused as much as 34% visual injury and reduced plant height by 23 to 28%, shoot dry weight by 35 to 39%, and yield by 20 to 30% in black and white bean market classes. Flumioxazin-applied PPI did not injure any market class. On the basis of this research, there is an acceptable margin of crop safety in these black and white bean cultivars only when flumioxazin is applied PPI. The two cranberry and kidney bean cultivars were tolerant to all rates of flumioxazin applied both PPI and PRE.

Weed management systems used by sweet corn growers, including the role of atrazine, are poorly characterized. Management records of 175 fields throughout the major sweet corn production areas of the Midwest were surveyed from 2005 to 2007. Seventy-four percent of sweet corn fields in the Midwest were grown in rotation with soybean or corn. Interrow cultivation was used on 48% of fields, and atrazine use was higher in those fields without interrow cultivation. A majority of fields (54%) received both PRE and POST herbicide applications. Mesotrione was applied below the registered use rate in two-thirds of the fields in which it was used POST. Atrazine rates in sweet corn were highest when the preceding crops were other vegetables, compared to preceding crops of soybean or corn. Selective herbicides are used extensively in U.S. sweet corn production, accounting for 94% of total weed management expenditures which average $123/ha. Growers treated 66% of fields with one or more applications of atrazine at an average total use rate of 1.35 kg ai/ha. The estimated annual net cost to replace atrazine in U.S. sweet corn production with the broad spectrum broadleaf herbicide, mesotrione, is $9.2 million.

Clomazone was applied preplant incorporated, preemergence, delayed preemergence, or postemergence and compared to pendimethalin, quinclorac, and thiobencarb for control of barnyardgrass in rice. Seven days after the clomazone postemergence application, all clomazone treatments except those applied postemergence controlled barnyardgrass ≥ 86%. At 49 d after the postemergence application, control of barnyardgrass with 0.56 and 0.67 kg/ha clomazone postemergence improved to 92 and 93%, respectively. Clomazone and quinclorac applied delayed preemergence generally controlled barnyardgrass less than 70%. Visible injury to rice was ≤ 18% 7 d after emergence and had declined to less than 10% when evaluated 7 d after postemergence treatments. Rice yields were higher with all treatments compared to the nontreated control.

Florida beggarweed germination in laboratory experiments was highest between 21 and 38 C and at osmotic potentials above −0.2 MPa, with complete germination inhibition below −0.8 MPa. Patterns of seedling emergence in the field corresponded to timing and size of rainfall events in relation to the time of soil disturbance. Smaller percentage total seasonal emergence was observed following large rainfall events where soil had not been disturbed compared with plots recently disturbed, and soil disturbance not followed by rainfall did not promote major weed flushes.

Barnyardgrass [Echinochloa crus-galli (L.) Beauv. ♯3 ECHCG], originally from Europe and India, now ranges from latitude 50 N to 40 S, in both temperate and tropical habitats (12). It is a serious weed problem in 42 countries and is found in at least 27 more (11). It is the world's principal weed of rice (12) and likely has been for a long time: barnyardgrass is recognizable in Chinese drawings from 1590 (13).

Carryover potential of imazaquin (0.14 kg ai ha−1), chlorimuron plus metribuzin (0.06 + 0.36 kg ha−1), and fomesafen (0.28 kg ha−1) to snap bean, watermelon, cucumber, mustard, and sunflower was evaluated in Arkansas in 1987 to 1989. Crops were direct-seeded into treated plots at various times after application. Imazaquin and chlorimuron plus metribuzin injured sunflower, watermelon, cucumber, and mustard when planted 16 wk following application in one of two years. Fomesafen injured all crops initially but did not injure snap bean, sunflower, watermelon, and cucumber planted 16 wk after application. In experiments in which herbicides were applied to soybean, fall-planted spinach and mustard were injured in one of two years.

Glyphosate-resistance evolution in weeds is evident globally, especially in areas where transgenic glyphosate-resistant crops dominate. Resistance to glyphosate is currently known in 16 weed species, including rigid ryegrass in Australia. Following the first report of glyphosate resistance in 1998, there are now 78 documented glyphosate-resistant populations of rigid ryegrass in grain-growing regions of southern Australia. In some regions where glyphosate-resistance evolution has already occurred in rigid ryegrass, transgenic glyphosate-resistant canola was introduced in 2008, further highlighting the need to monitor glyphosate-resistance evolution in weeds. A rigid ryegrass population (WALR70) was collected in 2005 from a crop field in Esperance, Western Australia, after it had survived applications of glyphosate. Dose–response experiments confirmed resistance in the population, with the glyphosate rate resulting in 50% mortality (LD50) for WALR70 being 11 times greater than that for a susceptible biotype. The WALR70 population also had low levels of resistance to some acetyl coenzyme A carboxylase (ACCase)- and acetolactate synthase (ALS)-inhibiting herbicides (diclofop, fluazifop, clodinafop, tralkoxydim, chlorsulfuron, and imazethapyr), but was susceptible to other herbicide modes of action, such as atrazine, trifluralin, and paraquat. Two other rigid ryegrass populations assessed in this study were also confirmed to be resistant to glyphosate. The increasing number of glyphosate-resistant rigid ryegrass populations in Australia is of concern to growers because of the importance of glyphosate in intensive cropping systems and the introduction of glyphosate-resistant canola to this region.

Field experiments were conducted in 1994 and 1995 at Vegreville, Legal, and Lacombe, AB, to determine the effects of a preharvest application of glyphosate on seedling emergence and growth of field pea. Glyphosate was applied at 0.9 kg ai/ha at each of the three crop development stages, as determined by seed moisture content (SMC), to determinate (‘Ascona’ and ‘Radley’) and indeterminate (‘Miko’ and ‘Trapper’) cultivars. Applying glyphosate when the SMC was less than 30% had little to no effect on seedling emergence but reduced seedling shoot fresh weight in two of six experiments. Applying glyphosate at SMC above 40% reduced seedling emergence and shoot fresh weight in two and three of the six experiments, respectively. Reductions in seedling emergence and shoot fresh weight were greater from seeds collected from the top than from seeds collected from the bottom one-third of sprayed plants. Differences in response between determinate and indeterminate cultivars occurred, but there was no consistent trend. Given the variable maturity in most fields and on individual pea plants, applications of preharvest glyphosate to peas destined for seed production may decrease seed germination and biomass accumulation.

This study assessed the tolerance of ‘Midlawn’ (Cynodon dactylon × C. transvaalensis) and ‘OKS 91-11’ (C. dactylon) bermudagrass to commonly used postemergence herbicides and compared visual assessment with vehicle-mounted optical sensing (V-MOS) for evaluating herbicide phytotoxicity. Two postemergence herbicides were applied to mature stands of Midlawn and OKS 91-11 at two and four times label rates, and seven postemergence herbicides were applied at standard and two times label rates. Visual evaluation and spectral assessments were made for turf color 2, 7, 14, and 21 d after treatment (DAT). Triclopyr and triclopyr plus clopyralid at 2× and 4× label rates caused significant damage on OKS 91-11 and Midlawn bermudagrass in both July and September experiments. MSMA at 2× rate and MSMA + metribuzin at 1× and 2× rate caused up to 73% color reductions that disappeared within 21 DAT in both cultivars. During July, 2,4-D plus mecoprop plus dicamba at the 2× rate caused at least 18% injury to Midlawn bermudagrass for 21 d. Metribuzin was safe at the 1× rate but caused significant injury for up to 7 d at the 2× rate. Imazaquin and halosulfuron-methyl each caused significant damage on one rating date. Pronamide caused no change in color regardless of rate or time of application. OKS 91-11 tolerated 2× rates of 2,4-D plus mecoprop plus dicamba better than Midlawn, but cultivar responses to other herbicide treatments were similar. V-MOS was effective for measuring green color reduction on bermudagrass turf. V-MOS and visual evaluation were linearly related (P < 0.01) at a strength of r = 0.58. Statistical results obtained using visual rating and V-MOS were the same in 86% of all cases.

Eight polymers capable of forming aqueous gels were compared for their capacity to retain hydration over time, to promote spore germination, and to prolong the viability of germinated spores (= germlings) of Alternaria cassiae, a bioherbicide agent for sicklepod. When compared at a standard 0.1% w/w (gel/water) concentration, the eight gels retained hydration for 6 d with no significant differences among them in the rate of dehydration. The best concentration of each gel that yielded 95 to 100% spore germination within 6 h after hydration was then chosen, and the gels were compared at these concentrations to determine the duration of effectiveness of the gels. The effectiveness was rated on the basis of the proportions of alive germlings versus germinated spores and alive germlings versus total spores, determined with the aid of a fluorescent vital stain. Based on these two parameters, the most effective gel was Kelzan® xanthan gum. However, all gels supported > 50% alive germlings over a period of 1 wk, suggesting that the addition of any of these polymers to the inoculum suspension should enable the fungal propagules to remain moist for a prolonged period, benefit from the high ambient moisture to improve germination, and promote disease development. Accordingly, seven of these gels were tested for their ability to enhance pathogenicity of a mycelial inoculum of A. eichhorniae, a bioherbicide agent for waterhyacinth. Gellan gum and Kelgin®-HV were most effective in promoting disease, followed by Evergreen® 500 polyacrylamide, and Kelgin®-LV, Metamucil®, Kelzan® xanthan gum, and N-Gel™ were no better than the control inoculum without any gel. Thus, the gels may have differential effects on different fungi and inoculum types. Nonetheless, the results confirm the utility and feasibility of hydrophilic gels as formulating materials for bioherbicides.

The effect of barley seeding rate and row spacing, and triallate, diclofop, and difenzoquat herbicide rate on barley grain yield and quality, and wild oat control were evaluated in field experiments near Bonners Ferry, Idaho, in 1989 and 1990. The purpose of the study was to develop integrated control strategies for wild oat in spring barley. Barley row spacing (9 and 18 cm) did not affect barley grain yield. Barley grain yield was greatest when barley was seeded at 134 or 201 kg ha–1 compared to 67 kg ha–1. Wild oat control increased as wild oat herbicide rate increased and barley grain yield was greatest when wild oat herbicides were applied. However, barley grain yield was similar when wild oat biomass was reduced by either 65 or 85% by applications of half and full herbicide rates, respectively. Net return was greatest when the half rate of herbicide was applied to 100 wild oat plants per m2 and was greatest when half or full herbicide rates were applied to 290 wild oat plants per m2. Net return increased when the seeding rate was increased to 134 or 201 kg ha–1 when no herbicide was applied and when 290 wild oat plants per m2 were present.

Field experiments were conducted in 1999 and 2000 at the Rice Research and Extension Center at Stuttgart, AR, on a DeWitt silt loam and at the Pine Tree Branch Experiment Station near Colt, AR, on a Calloway silt loam to evaluate the tolerance of 14 rice cultivars and four experimental cultivar lines to clomazone at 0.34 and 0.67 kg ai/ha applied preemergence. Early-season chlorosis 14 days after emergence (DAE) ranged from 1 to 21% in 1999 and 3 to 40% in 2000 when averaged over herbicide rate. The experimental cultivar line RU961096 was slightly more susceptible to clomazone than other cultivars and lines. However, RU9701041 was more tolerant to clomazone at 0.67 kg/ha 14 DAE than other cultivars and lines. By 28 DAE, all cultivars had <13% chlorosis in 1999 and <8% in 2000. The experimental cultivar line RU9601096 and cultivar Koshihikari did not recover as quickly as the other 16 cultivars and cultivar lines. Early-season chlorosis had no effect on days to 50% heading or yield for any of the cultivars evaluated.

Velvetleaf from Mississippi and Wisconsin and soybean (var. Williams) were grown in five temperature regimes (12/4, 19/11, 26/18, 33/25, and 40/32 C day/night) in controlled-environment chambers. Leaf appearance rates increased with temperature in both species, ranging from 0.06 to 0.69 leaves per day in velvetleaf and 0.07 to 0.38 leaves per day in soybean. The threshold temperature for leaf appearance in both species was 5 to 6 C. The largest leaves of both species were produced at 26/18 C. By 55 d after emergence, the greatest total leaf area per plant occurred at 26/18 C or above in both species. Reproductive development occurred earliest at 33/25 C in velvetleaf and at 26/18 C in soybean. This limited vegetative growth in velvetleaf more than in soybean. The weed/crop ratio for total leaf area increased with increasing temperature, indicating that velvetleaf probably would be more competitive with soybean under higher temperatures. The two populations of velvetleaf generally responded similarly to temperatures.

Field and greenhouse experiments were conducted to evaluate clethodim, CGA-362622, mixtures thereof, and sequential treatments for control of broadleaf signalgrass, fall panicum, goosegrass, and large crabgrass. In greenhouse experiments, clethodim alone provided 93 and 100% control of three- to four-leaf goosegrass at the low (105 g ai/ha) and high (140 g/ha) rates, respectively, whereas CGA-362622 did not control grasses in greenhouse or field experiments. Control of six- to eight-leaf goosegrass in the greenhouse with clethodim was 75% for the low rate and 89% for the high rate. Control of goosegrass in greenhouse studies was reduced at least 43 percentage points with CGA-362622 and clethodim at the high rate in mixture compared with control provided by clethodim at the high rate alone. When CGA-362622 and clethodim were applied in mixture in field studies, the effectiveness of the graminicide was decreased from > 97 to < 57% control for all annual grasses. Antagonism of clethodim activity was greater than that of the tank mixture when clethodim was applied 1 d after CGA-362622 on large crabgrass, goosegrass, and fall panicum. Clethodim applied 7 d before or after CGA-362622 controlled the four grass species as well as did clethodim applied alone. When CGA-362622 was applied to goosegrass alone, fresh weight accumulation stopped for a period of 4 d compared with untreated plants. Normal growth resumed after 4 d.