Effective, long-term wild oat management requires an integrated approach that uses management techniques beyond simple herbicide application. A 5-yr (1996 to 2000) zero tillage study was conducted to assess the influence of barley harvest timing on wild oat densities in subsequent years at Lacombe, AB, Canada and Melfort, SK, Canada. Harvest timings included barley harvested 1 wk after heading (early), approximately 14 to 16 d later at the soft dough stage (normal), and at maturity (grain). In the absence of herbicides, wild oat densities decreased in silage plots harvested early and increased in grain plots. Reductions were more distinct at Lacombe where barley phenological differences and whole plant moisture contents between early and normal silage harvests were greater than at Melfort. Half rates of wild oat herbicides (ICIA 0604 and imazamethabenz) did not augment reductions in wild oat densities after early silage harvest, but did improve wild oat management after normal silage harvest, and in grain production. At Lacombe, early silage harvest reduced wild oat densities more than did herbicides in grain production. Similar trends were apparent at Melfort but were not statistically significant. Early barley silage harvests may be an effective integrated weed management tool for wild oat.

A field experiment was conducted for 2 yr near Scottsbluff, NE, to evaluate the growth and yield response of nine commercial sugarbeet cultivars to five postemergence herbicide mixtures applied two times. Sugarbeet cultivars varied in their response to herbicides. Three of the five postemergence herbicide mixtures reduced sugarbeet leaf area at 9 wk after planting (WAP), while two treatments had no significant effect. Root yield reductions from herbicide treatments ranged from 3 to 11% averaged over the nine cultivars. Two applications of desmedipham plus phenmedipham at 180 plus 180 g/ha reduced root yield 3% compared to untreated plots. Two applications of clopyralid at 100 g/ha, triflusulfuron at 18 g/ha, or ethofumesate at 160 g/ha plus desmedipham plus phenmedipham resulted in a 17, 29, and 22% reduction in leaf area at 9 WAR respectively, and a 6, 8, and 6% reduction in root yield, respectively, compared to untreated plots. Sethoxydim at 280 g/ha plus desmedipham plus phenmedipham did not cause additional sugarbeet injury.

Several labeled herbicide treatments reduced winter wheat height and grain yield when applied at different growth stages in 1984 and 1985. Yield reductions were related to reduced spike production. Wheat height and yield generally were greatest when herbicides were applied at Zadoks' Stage 29 and lowest at Stage 13. Herbicide treatments did not affect wheat kernels per spike, kernel weight, volume weight, or germination either year. However, most herbicide treatments either increased or decreased seed protein content, depending on the year.

Trials were established in 2003, 2004, and 2005 in Ontario to determine the effects of residues of mesotrione, atrazine, and mesotrione plus atrazine 1 and 2 yr after application on broccoli, carrot, cucumber, onion, and potato. One yr after mesotrione application, injury was 43, 37, 18, 24, and 0% in broccoli, carrot, cucumber, onion, and potato, respectively. The addition of atrazine to mesotrione in the year before planting increased injury to 55, 53, 30, 42, and 3% in broccoli, carrot, cucumber, onion, and potato, respectively. Plant dry weight and yield were also decreased by mesotrione residues the year after application in all crops except potato. The addition of atrazine to mesotrione accentuated the reduction in dry weight and yield in broccoli, carrot, cucumber, and onion. There was no injury, or reductions in dry weight or yield in any crop planted 2 yr after application of mesotrione alone or in tank mix with atrazine. A recropping interval of 2 yr is recommended following applications of mesotrione or mesotrione plus atrazine for broccoli, carrot, cucumber, and onion. Potato can be safely planted the year following application of mesotrione plus atrazine.

Johnsongrass is a troublesome weed infesting spring–summer crops. Poor control of johnsongrass after fluazifop-p-butyl treatments has been reported in central to northern Italy. Greenhouse and outdoor dose–response experiments revealed that four populations were highly resistant to fluazifop-p-butyl. All four were cross-resistant to other aryloxyphenoxypropionate (FOP) herbicides—propaquizafop, quizalofop, and haloxyfop. The resistance indexes ranged between 8 and 25 for propaquizafop and quizalofop, whereas a greater variability between populations was detected in response to haloxyfop. Conversely, cycloxydim and clethodim determined only a shift in the susceptibility with resistance index (RI) values of 2 to 3. Molecular analyses revealed that resistant plants possessed an insensitive acetyl coenzyme-A carboxylase (ACCase) target enzyme due to an Ile-to-Asn substitution at codon 2041. To our knowledge, this is the first report of such a mutation endowing ACCase resistance in johnsongrass. A molecular marker (CAPS assay) was developed for its rapid detection. Alternative mode of action herbicides S-metolachlor and nicosulfuron controlled all the FOP-resistant populations. Only a few chemical options are still available, and they have different efficacy on germinating seeds and sprouting rhizomes. To maintain efficacy over time, herbicides should be integrated with agronomic practices.

Residual herbicides are routinely recommended to aid in control of glyphosate-resistant (GR) Palmer amaranth in cotton. Acetochlor, a chloroacetamide herbicide, applied PRE, controls Palmer amaranth. A microencapsulated (ME) formulation of acetochlor is now registered for PRE application in cotton. Field research was conducted in North Carolina to evaluate cotton tolerance and Palmer amaranth control by acetochlor ME alone and in various combinations. Treatments, applied PRE, consisted of acetochlor ME, pendimethalin, or no herbicide arranged factorially with diuron, fluometuron, fomesafen, diuron plus fomesafen, and no herbicide. The PRE herbicides were followed by glufosinate applied twice POST and diuron plus MSMA directed at layby. Acetochlor ME was less injurious to cotton than pendimethalin. Acetochlor ME alone or in combination with other herbicides reduced early season cotton growth 5 to 8%, whereas pendimethalin alone or in combinations injured cotton 11 to 13%. Early season injury was transitory, and by 65 to 84 d after PRE treatment, injury was no longer noticeable. Before the first POST application of glufosinate, acetochlor ME and pendimethalin controlled Palmer amaranth 84 and 64%, respectively. Control by acetochlor ME was similar to control by diuron plus fomesafen and greater than control by diuron, fluometuron, or fomesafen alone. Greater than 90% control was obtained with acetochlor ME mixed with diuron or fomesafen. Palmer amaranth control was similar with acetochlor ME plus a full or reduced rate of fomesafen. Acetochlor ME controlled large crabgrass and goosegrass at 91 and 100% compared with control at 83 and 91%, respectively, by pendimethalin. Following glufosinate, applied twice POST, and diuron plus MSMA, at layby, 96 to 99% control was obtained late in the season by all treatments, and no differences among herbicide treatments were noted for cotton yield. This research demonstrated that acetochlor ME can be safely and effectively used in cotton weed management programs.

Colletotrichum gloeosporioides f. sp. malvae (C.g.m.) was evaluated under greenhouse conditions for round-leaved mallow control in combination with the following herbicides: bromoxynil plus MCPA (1:1), diclofop, imazethapyr, metribuzin, sethoxydim, and 2,4-DB. Treatments consisted of C.g.m. and herbicide applied alone, tank mixed, and C.g.m. applied 48 h before, and 1, 24, and 72 h after herbicide. Split applications with bromoxynil plus MCPA, imazethapyr, metribuzin, (C.g.m. before or after) and sethoxydim (C.g.m. before) enhanced round-leaved mallow control over C.g.m. applied alone. However, diclofop or 2,4-DB tank mixed or applied in a split application with C.g.m. did not improve round-leaved mallow control over C.g.m. applied alone. Bromoxynil plus MCPA, metribuzin, 2,4-DB, and imazethapyr may be tank mixed with C.g.m. without significantly reducing round-leaved mallow control, unlike sethoxydim or diclofop which inhibited C.g.m. development. Dew period did not influence the effectiveness of bromoxynil plus MCPA applied 30 h before C.g.m., but round-leaved mallow control increased with increasing dew period for metribuzin applied 30 h before C.g.m.

Preplant applications of two 2,4-D formulations and dicamba were evaluated for injury to no-till soybean. Herbicides applied 28 or 21 d before planting (DBP) at 0.56 kg ae/ha for the 2,4-D formulations and 0.28 kg ae/ha for dicamba did not injure soybean. At 14 DBP soybean injury was lower (< 6%) with applications of 2,4-D than with dicamba (13% to 17%). Injury increased when herbicides were applied at 7 DBP with soybean injury from both 2,4-D (< 11%) and dicamba (< 38%). When the herbicides were applied at planting soybean injury was < 18% with the 2,4-D formulations and < 73% with dicamba. Soybean yields were unaffected by the injury from herbicides applied 21, 14, and 7 DBP. However, soybean yield was decreased to 870 kg/ha in 2005 when dicamba was applied at planting compared to the nontreated check (1,950 kg/ha)

Allelopathy has been suggested as a mechanism of interference in several weed species. Allelochemicals released from certain weed species influence the growth and yield of crop species. Several laboratory studies present circumstantial evidence of the occurrence of allelopathy as a causative agent in weed–crop agroecosystems. Field evidence, however, is still lacking. In this paper, the significance of field studies is argued in terms of a multifaceted approach to allelopathy, and mugwort is used as an example. Previous research demonstrated the allelopathic potential of mugwort; however, experiments were not carried out in a natural environment. Inderjit and Foy (1999) have demonstrated that chemical characteristics (pH, inorganic ions, and phenolics) of soil amended with mugwort leaf leachate were altered when compared to unamended soil. We have analyzed the mugwort-infested field soil and compared its chemical characteristics with those of amended soils. No definite trend, in terms of influence of mugwort on soil chemistry, was observed. Results indicate the importance of field studies in order to obtain ecologically relevant data from laboratory studies. Field situations are often complex in terms of the presence of interfering flora. Cyanobacteria, for example, play an important role in weed–crop interactions in rice paddy soils. Allelochemicals released from weed species present in the paddy field may influence nitrogen-fixing cyanobacteria in addition to their phytotoxic effects to the paddy crop. Significance of phytotoxic effects of weed species on crop growth, and N2-fixing potential of cyanobacteria in paddy soils is discussed.

The influence of four tillage systems, varying from intensive to zero tillage, on weed populations and the vertical distribution of weed seeds in the soil was determined at Alliance, Hairy Hill, and Wainwright in northeastern Alberta. The soil was sampled at two depths (0 to 5 and 5 to 10 cm) in fall. Weed seedling emergence in the greenhouse over the winter was assumed to represent the type and amount of weed seeds present in the soil seedbank. Emerged weed seedlings were also identified and counted in the field in spring. In the zero-tillage system, most of the weed seeds were close to the soil surface (0 to 5 cm) at Alliance and Wainwright but were deeper (5 to 10 cm) at Hairy Hill. The winter annuals, field pennycress, shepherd's-purse, and flixweed, and the summer annuals, wild buckwheat and common lambsquarters, increased in the soil seedbank as tillage was reduced, but the higher populations in the soil seedbank did not always result in higher spring seedling populations under zero tillage. In contrast to the seedbank, spring seedling populations of common lambsquarters at Alliance and field pennycress and ball mustard at Hairy Hill were lowest in the zero-tillage system, suggesting that the requirement for herbicides for controlling these weeds in the crop may be least under zero tillage. Both soil seedbank and spring seedling populations of shepherd's-purse at Wainwright and Alliance and of flixweed at Alliance were highest in the zero-tillage system. At Alliance, wild buckwheat seedling emergence in the spring tended to be highest in the minimum-tillage system (one tillage operation prior to seeding). Both soil seedbank and spring seedling populations of green foxtail decreased as tillage was reduced, indicating that green foxtail should become less of a problem under reduced tillage.

The efficacy of preemergence (PRE) applications of ethalfluralin or pendimethalin incorporated with irrigation was compared with mechanical preplant incorporated (PPI) applications at equivalent rates in peanut. PRE applications of herbicides followed by irrigation were as effective as PPI applications in controlling Texas panicum, southern crabgrass, and crowfootgrass. Split PPI/PRE applications of ethalfluralin were more effective than PPI applications in controlling Texas panicum in 2 of 3 yr. Sequential postemergence applications of clethodim or sethoxydim increased the control of Texas panicum when ethalfluralin or pendimethalin controlled Texas panicum less than 82%. No differences in peanut yield were observed between PPI or PRE applications of either ethalfluralin or pendimethalin.

Four field experiments were conducted during 1988 and 1989 to determine the effects of POST application of nicosulfuron on quackgrass control in conventional field corn. A single application of nicosulfuron at 35 to 70 g ha–1 applied to four- to six-leaf quackgrass controlled over 90% of quackgrass five weeks after treatment. Nicosulfuron at 35 g ha–1 applied at the one- to three-leaf stage was not as effective as the same rate applied at the four- to six-leaf stage. When nicosulfuron at 35 g ha–1 was applied to four- to six-leaf quackgrass, over 80% of the quackgrass regrowth was controlled one year later. Nicosulfuron did not injure ‘Agway 584S’ corn at the highest rate (140 g ha–1) tested and did not reduce silage or grain yield.

Largeseed dodder is the most troublesome weed in alfalfa fields in the high desert of Southern California. Preemergence treatment with trifluralin controls dodder early in the season, but, as the season progresses, control declines. A method was needed to control attached dodder plants that escaped preemergence treatment. Flail mowing was compared to burning with a handheld propane-fueled weed burner. These methods were equally effective for controlling attached dodder, but flail mowing was more economical, and less injurious to alfalfa yield and stand density. Burning dodder patches at the end of the season reduced dodder seed viability by an average of 99%. Thus, we propose the use of a three tiered integrated approach consisting of PRE herbicide treatment followed by flail mowing in mid-season to control escaped dodder and burning at the end of the season to reduce dodder seed.

Field studies were conducted in 1999, 2000, and 2001 to investigate weed control and glyphosate-resistant corn tolerance to postemergence applications of mesotrione at 70, 105, and 140 g ai/ha applied with and without glyphosate at 560 g ai/ha. Mesotrione alone and mixed with glyphosate controlled smooth pigweed greater than 97% and common lambsquarters 93 to 99%. Control of common ragweed and morningglory species was variable. Common ragweed control was generally best when mesotrione was applied at 105 or 140 g/ha, and control increased only in 2000 with the addition of glyphosate. Giant foxtail control was below 25% with all rates of mesotrione, but mixtures of mesotrione plus glyphosate controlled giant foxtail 65 to 75%. Mesotrione injured glyphosate-resistant corn 4 to 24% when averaged over glyphosate rates, and injury was usually increased by higher mesotrione rates, with rainfall after herbicide applications, and in mixtures with glyphosate. Injury was transient and did not reduce corn yields. Mesotrione injury on glyphosate-resistant corn was confirmed in the greenhouse, where all mesotrione treatments reduced glyphosate-resistant corn biomass 9 to 23% compared with the nontreated check.

Eight sweet corn cultivars differed in response to 35 g ai ha–1 nicosulfuron or 42 g ai ha–1 primisulfuron. ‘Merit’ sweet corn was killed 4 wk after nicosulfuron or primisulfuron application. Nicosulfuron and primisulfuron reduced height of Merit, 'Silver Queen’, 'Silverado’ and ‘How Sweet It Is'. Ear number of How Sweet It Is, ‘Pinnacle’ and Silverado was reduced by primisulfuron. ‘Landmark’, Silver Queen, and 'Sweetie 76’ were the most tolerant cultivars to nicosulfuron and primisulfuron with yield similar to that of the control.

Literature concerning interactions between herbicides and insects is reviewed. Herbicides can be toxic to insects or can affect them indirectly, such as by destroying food supplies, but they usually can be used with proper application timing without affecting insects adversely. Herbicides and biocontrol insects can interact either favorably or unfavorably depending on the life cycle stage of weed and insect, effect on predatory insects, changes in food quality, mobility of the biocontrol insect, and impact of herbicides on weed growth. Thus, interactions between a biocontrol insect and herbicide can be antagonistic, additive, complementary, or synergistic. Split-plot techniques to evaluate these interactions at an early stage of insect establishment are proposed to improve weed biocontrol.

Fluometuron at 1.1 kg ai/ha was applied postemergence (over-the-top) to cotton in the V3 to V4 stage to determine effects on flower and boll production, yield, and fiber quality. Treated plants produced more bolls but boll weight was reduced. Lint yield was not affected. Flower and boll production during the first 2 weeks of flowering were reduced, but treated plants produced more flowers and bolls during mid- and late bloom. A delay in sympodia development delayed development of fruiting structures. Fluometuron treatment promoted sympodia development on monopodia at nodes three and four. Fiber micronaire was reduced in 1 of 2 yr. Fiber strength, length, and length uniformity were not affected.

Saflufenacil (BAS 800H) is a new herbicide being developed by BASF for PRE broadleaf weed control in corn. Field studies were conducted at two Ontario locations in 2006 and 2007 to evaluate the tolerance of field corn to PRE and POST (spike and two- to three-leaf corn) applications of saflufenacil at 50, 100, and 200 g ai/ha with and without an adjuvant (surfactant blend + solvent [petroleum hydrocarbons]; 1% v/v). Saflufenacil applied PRE reduced corn height by as much as 12% with the highest rate of 200 g/ha; however, corn yield was not affected. When saflufenacil was applied without an adjuvant to corn at the spike stage, injury was as much as 12%, 7 d after treatment (DAT). However, corn height and yield were not affected. Saflufenacil applied POST to two- to three-leaf corn at 50 to 200 g/ha without an adjuvant resulted in as much as 25% injury and reduced corn height 31% but did not affect yield. Adding an adjuvant to POST applications of saflufenacil caused as much as 4 and 99% injury, reduced corn height 13 and 77%, and reduced corn yield 0 and 59% when applied to corn at the spike and at the two- to three-leaf stages, respectively. Based on these results, saflufenacil applied PRE can be safely used in corn at rates up to 200 g/ha. Saflufenacil applied to corn at the spike and two- to three-leaf stage at 50 or 100 g/ha without an adjuvant demonstrated acceptable corn tolerance and may allow for the use of saflufenacil beyond the proposed PRE use pattern. In contrast, applying saflufenacil POST with an adjuvant to spike and two- to three-leaf stage corn resulted in unacceptable injury and yield losses in field corn.

Field experiments conducted at four locations in Georgia and two locations in Florida during 1992 and 1993 evaluated AC 263,222 application rates and timings, systems, and mixtures for weed control, peanut injury, and yield. All rates of AC 263,222 applied early POST (EPOST) or POST controlled Ipomoea morningglories and smallflower morningglory at least 90%, and purple and yellow nutsedge at least 81%. Florida beggarweed and sicklepod control generally was highest when metolachlor was applied PPI followed by AC 263,222 applied EPOST at 71 g/ha, AC 263,222 at 27 or 36 g/ha plus bentazon plus paraquat applied POST, or with bentazon plus paraquat applied EPOST followed by AC 263,222 applied POST at 36 or 53 g/ha. Acifluorfen and acifluorfen plus bentazon reduced Florida beggarweed and sicklepod control at several locations when applied in mixture with AC 263,222. Common ragweed and hairy indigo control were 85 to 95% with bentazon plus paraquat applied EPOST followed by AC 263,222 applied POST at 36 or 53 g/ha. Highest peanut yields were obtained with treatments providing high levels of weed control.

The practical application of yield loss prediction models using relative leaf area of weeds is limited due to the lack of a quick and accurate method of leaf area estimation. Leaf cover (the vertical projection of plant canopy on the ground) can be used to approximate leaf area at early stages of plant development. An automated digital image analysis system for measuring leaf cover has been developed. The system has an operator-assisted module aimed at validating the automated functions. The objective of this research was to demonstrate the accuracy of the operator-assisted module under different weed–crop conditions. A laboratory experiment was conducted using simulated weed–crop populations. Two additional field experiments were conducted using corn in competition with: (1) common lambsquarters, barnyardgrass, or a mixture of both species, and (2) a natural weed community. In the laboratory experiment, a narrow linear relation was observed between leaf cover estimated with the operator-assisted module and leaf area measured with an optical area meter (r 2 > 0.98). In field experiments, the regression between corn leaf cover estimated by the operator-assisted module and corn leaf area measured with the optical area meter was not as good (r 2 < 0.55). The poor performance of the module was probably due to the overlapping and the architecture of corn leaves (especially unexpanded leaves). Nevertheless, the system showed high precision in estimating leaf area of both grassy weeds and broadleaf weeds (r 2 > 0.89). Generally, the accuracy of the estimates decreased as the growth stage became more advanced. Apart from its initial purpose as a calibration tool for the automated system, the operator-assisted module can have several potential research applications. It can be used: (1) as an alternative to destructive leaf area measurement at early stages of plant development, (2) as a tool in the study of plant competitive ability, and (3) as an objective and quantitative support to visual observations.