Wk After Emergence Research Articles

Rice tolerance to acetochlor with a fenclorim seed treatment

AbstractRice producers in the United States need effective herbicides to control problematic weeds. Previous research has demonstrated that acetochlor can provide in-season weed control in rice; however, undesirable injury is common. Thus, trials were initiated in 2020 and 2021 to evaluate 1) rice cultivar tolerance to microencapsulated (ME) acetochlor with the use of a fenclorim seed treatment at 2.5 g ai kg−1 of seed; 2) a dose-response of a fenclorim seed treatment with ME acetochlor; and 3) rice tolerance to fenclorim and ME acetochlor under cool, wet conditions. For all trials, acetochlor was applied delayed-preemergence (4 to 7 d after planting). In the dose-response trials and in the presence of acetochlor, the fenclorim seed treatment rate of 2.5 g ai kg−1 reduced rice injury and increased rice plant heights and shoot numbers relative to acetochlor without fenclorim, and plant heights and shoot numbers were comparable to those of the nontreated control in all evaluations. In the cultivar screening, 14 of 16 cultivars exhibited <20% injury with acetochlor at 1,260 g ai ha−1 and fenclorim at 2.5 g ai kg−1 2 wk after emergence (WAE) at the Pine Tree Research Station (PTRS). At the Rice Research and Extension Center (RREC) 2 and 4 WAE and at PTRS 4 WAE, all cultivars exhibited <20% injury with acetochlor and fenclorim. The fenclorim seed treatment in the presence of acetochlor provided comparable rice plant height, shoot numbers, groundcover, and rough rice yield to that of the nontreated control. Under cool, wet conditions, rice injury without fenclorim ranged from 15% to 60% with acetochlor at 1,050 g ai ha−1, whereas injury from acetochlor with the fenclorim seed treatment ranged from 0% to 20%. Based on the results of these experiments, the fenclorim seed treatment appears to safen an assortment of rice cultivars from injury caused by ME acetochlor.

The interaction of pyroxasulfone and flumioxazin applied preemergence for the control of multiple-herbicide-resistant waterhemp (Amaranthus tuberculatus) in soybean

AbstractSix field experiments were conducted to investigate any interaction between pyroxasulfone and flumioxazin on soybean tolerance and control of multiple-herbicide-resistant (MHR) waterhemp in soybean during 2016 and 2017 in Ontario, Canada. There was a synergistic increase in soybean injury with the co-application of pyroxasulfone and flumioxazin at all rates evaluated at 2 wk after emergence (WAE), the two highest rates evaluated (134/106 and 268/211 g ai ha–1) at 4 WAE, and the highest rate (268/211 g ai ha–1) evaluated at 8 WAE. Soybean injury with all pyroxasulfone and flumioxazin treatments was transient and had no adverse effect on soybean grain yield. Pyroxasulfone applied preemergence at 45, 89, 134, and 268 g ai ha–1 controlled MHR waterhemp up to 72%, 89%, 92%, and 95%, respectively. Flumioxazin applied preemergence at 35, 70, 106, and 211 g ai ha–1 controlled MHR waterhemp up to 78%, 90%, 93%, and 96%, respectively. Pyroxasulfone/flumioxazin applied preemergence at 45/35, 89/70, 134/106, and 268/211 g ai ha–1 controlled MHR waterhemp up to 92%, 96%, 98%, and 100%, respectively. There were no significant antagonistic or synergistic interactions for the control of MHR waterhemp with pyroxasulfone/flumioxazin at rates evaluated except at 268/211 g ai ha–1, which provided a synergistic increase in MHR waterhemp control at 4 WAE. The MHR waterhemp biomass and density reductions followed a trend similar trend to visible control. Pyroxasulfone/flumioxazin at 268/211 g ai ha–1 caused a synergistic response in biomass reduction (9% difference). Based on these results, there is an additive increase in MHR waterhemp control and potential for a synergistic increase in soybean injury with the co-application of pyroxasulfone plus flumioxazin.

Biologically effective dose of flumioxazin and pyroxasulfone for control of multiple herbicide–resistant waterhemp (Amaranthus tuberculatus) in soybean

AbstractTwo studies were conducted to ascertain the biologically effective dose (BED) of flumioxazin and pyroxasulfone for multiple herbicide–resistant (MHR) waterhemp [Amaranthus tuberculatus (Moq.) Sauer] control in soybean [Glycine max (L.) Merr.] in southwestern Ontario, Canada, during 2016 and 2017. In the flumioxazin study, the predicted flumioxazin doses for 50%, 80%, and 90% MHR A. tuberculatus control were 19, 37, and 59 g ai ha−1 at 2 wk after application (WAA) and 31, 83, and 151 g ai ha−1, respectively, at 12 WAA. The predicted flumioxazin doses to cause 5% and 10% soybean injury were 129 and 404 g ai ha−1, respectively, at 2 wk after emergence (WAE), and the predicted flumioxazin doses to obtain 50%, 80%, and 95% of the weed-free control plot’s yield were determined to be 3, 14, and 65 g ai ha−1, respectively. In the pyroxasulfone study, the predicted pyroxasulfone doses that provided 50%, 80%, and 90% MHR A. tuberculatus visible control were 25, 50, and 88 g ai ha−1 at 2 WAA and 41, 109, and 274 g ai ha−1 at 12 WAA, respectively. The dose of pyroxasulfone predicted for 80% reduction in MHR A. tuberculatus density was 117 g ai ha−1, and the doses of pyroxasulfone predicted for 80% and 90% reduction in A. tuberculatus biomass were 204 and 382 g ai ha−1, respectively. The predicted doses of pyroxasulfone that caused 5% and 10% injury in soybean at 2 WAE were 585 and 698 g ai ha−1, respectively. The predicted doses of pyroxasulfone required to obtain 50%, 80%, and 95% yield relative to the weed-free plots were 6, 24, and 112 g ai ha−1, respectively. Flumioxazin and pyroxasulfone applied preemergence at the appropriate doses provided early-season MHR A. tuberculatus control in soybean.

Sensitivity of Dry Bean to Herbicides Applied Preplant for Glyphosate-Resistant Horseweed Control in a Strip-Tillage Cropping System

AbstractDuring 2016 and 2017, four field experiments were conducted at Huron Research Station near Exeter, ON, to evaluate the sensitivity of dry bean grown under a strip-tillage cropping system, to potential herbicides for the control of glyphosate-resistant (GR) horseweed. At 8 wk after emergence (WAE), saflufenacil, metribuzin, saflufenacil+metribuzin, 2,4-D ester, flumetsulam, cloransulam-methyl, and chlorimuron-ethyl caused 13% to 32%, 8% to 52%, 32% to 53%, 5% to 7%, 13% to 21%, 16% to 29%, and 23% to 43% visible injury in dry beans, respectively. Saflufenacil decreased aboveground biomass 65% in kidney bean and 80% in white bean. Metribuzin decreased biomass 82% in kidney bean and 50% in white bean. Saflufenacil+metribuzin decreased biomass 88% in kidney bean, 68% in small red bean, and 80% in white bean. Chlorimuron-ethyl decreased biomass 40% in white bean. There was no decrease in dry bean biomass with the other herbicides evaluated. Metribuzin and saflufenacil+metribuzin reduced kidney bean seed yield 72% and 76%, respectively. Saflufenacil+metribuzin, flumetsulam, cloransulam-methyl, and chlorimuron-ethyl reduced small red bean seed yield 39%, 27%, 30%, and 54%, respectively. Saflufenacil, metribuzin, saflufenacil+metribuzin, flumetsulam, cloransulam-methyl, and chlorimuron-ethyl reduced seed yield of white bean 52%, 32%, 62%, 33%, 42%, and 62%, respectively. There was no decrease in dry bean yield with the other herbicides evaluated. Among herbicides evaluated, 2,4-D ester caused the least crop injury with no effect in dry bean seed yield.

Effect of Growth Stage on Cotton Response to a Sublethal Concentration of Dicamba

AbstractThe introduction of auxin herbicide weed control systems has led to increased occurrence of crop injury in susceptible soybeans and cotton. Off-target exposure to sublethal concentrations of dicamba can occur at varying growth stages, which may affect crop response. Field experiments were conducted in Mississippi in 2014, 2015, and 2016 to characterize cotton response to a sublethal concentration of dicamba equivalent to 1/16X the labeled rate. Weekly applications of dicamba at 35 g ae ha−1were made to separate sets of replicated plots immediately following planting until 14 wk after emergence (WAE). Exposure to dicamba from 1 to 9 WAE resulted in up to 32% visible injury, and exposure from 7 to 10 WAE delayed crop maturity. Exposure from 8 to 10 and 13 WAE led to increased cotton height, while an 18% reduction in machine-harvested yield resulted from exposure at 6 WAE. Cotton exposure at 3 to 9 WAE reduced the seed cotton weight partitioned to position 1 fruiting sites, while exposure at 3 to 6 WAE also reduced yield in position 2 fruiting sites. Exposure at 2, 3, and 5 to 7 WAE increased the percent of yield partitioned to vegetative branches. An increase in percent of yield partitioned to plants with aborted terminals occurred following exposure from 3 to 7 WAE and corresponded with reciprocal decreases in yield partitioned to positional fruiting sites. Minimal effects were observed on fiber quality, except for decreases in fiber length uniformity resulting from exposure at 9 and 10 WAE.

Influence of Competitive Duration of Blessed Milkthistle (Silybum marianum) with Wheat

AbstractBlessed milkthistle is considered to be a noxious weed in irrigated and rainfed areas of Pakistan due to its strong allelopathic effects on food crops. For sustainable wheat production, it is necessary to know the critical time for weed removal (CTWR) for blessed milkthistle to allow wheat growers to get maximum benefit from control of this weed. A field study was conducted in 2014 and 2015 at the College of Agriculture, University of Sargodha, Pakistan, to investigate the CTWR of blessed milkthistle in wheat. The field experiments were designed with seven treatments; weed free (control); 2, 3, 4, 5, and 6 wk after emergence (WAE); and weedy check. At 6 WAE, a significant reduction was noted in plant height (8% and 17%), number of productive tillers per square meter (16% and 16%), spike length (23% and 54%), grains per spike (13% and 34%), 1,000-grain weight (14% and 37%), grain yield (20% and 21%), and biological yield (24% and 50%) compared with control (weed-free plots) during 2014 and 2015, respectively. The logistic model supports the field study results and suggests that blessed milkthistle’s CTWR for wheat is 1 to 5 WAE based on acceptable yield losses of 5% to 15% during both years. The experimental results and logistic model indicate that blessed milkthistle should be controlled within 1 to 5 WAE to get better wheat crop harvests without compromising farmers’ profits. To our knowledge, this is the first study ever in Pakistan regarding the CTWR in terms of WAE of blessed milkthistle and could help other scientists create weed control strategies for other areas of the country.

Response of dry bean to Group 15 herbicides applied preplant incorporated

A study consisting of four field experiments was conducted over a 2-yr period (2016, 2017) near Exeter and Ridgetown, ON, to compare the tolerance of adzuki, kidney, small red, and white beans to four Group 15 herbicides including pethoxamid (1200 and 2400 g a.i. ha−1), S-metolachlor (1600 and 3200 g a.i. ha−1), dimethenamid-P (693 and 1386 g a.i. ha−1), and pyroxasulfone (100 and 200 g a.i. ha−1) applied preplant incorporated (PPI). At 1 wk after emergence (WAE), pethoxamid, S-metolachlor, dimethenamid-P, and pyroxasulfone caused as much as 22%, 17%, 38%, and 15% adzuki bean injury, respectively. The injury decreased with time; at 8 WAE, pethoxamid, S-metolachlor, dimethenamid-P, and pyroxasulfone applied PPI caused as much as 3%, 4%, 12%, and 7% adzuki bean injury, respectively. The injury was lower in other market classes of dry bean. At 1, 2, and 4 WAE, pethoxamid, S-metolachlor, dimethenamid-P, and pyroxasulfone caused as much as 4%, 2%, 4%, and 14% injury in kidney bean, 3%, 2%, 4%, and 12% injury in small red bean, and 5%, 3%, 6%, and 13% injury in white bean, respectively. However, the injury at 8 WAE was 5% or less in kidney, small red, and white beans with all Group 15 herbicides evaluated. Based on this research, pyroxasulfone was the most injurious to dry beans, it reduced plant height as much as 15% and seed yield as much as 17%. The Group 15 herbicides evaluated were more injurious to adzuki bean than kidney, small red, or white beans.

Role of Edamame (Glycine max) Seed Size in Early-Season Crop–Weed Interactions

AbstractEdamame [Glycine max(L.) Merr.] differs from grain-type soybean in several aspects, one being that edamame seeds are 65% to 100% larger than grain-type soybean seed. Crop seed size has implications for weed management in grain-type soybean; however, the extent to which this observation holds true for edamame is unknown. Because weed interference continues to be a barrier to domestic edamame production, the objective was to quantify the effect of edamame seed size on the crop’s ability to tolerate weed interference (CT) and the crop’s ability to suppress weeds (WSA). Five edamame cultivars plus one grain-type cultivar were each sorted to create “small” and “large” seed size classes. Seed lots were included in a split–split plot design, whereby an additional experimental factor was presence or absence of velvetleaf (Abutilon theophrastiMedik.). Crop and weed emergence and growth were monitored through 8 wk after emergence (WAE). Crop plants from large seed had higher tolerance toA. theophrastithan plants from small seed, as evidenced by crop height, area, and biomass. Edamame seed size had little effect on WSA; however, crop cultivars differentially reducedA. theophrastileaf area and biomass at 4 and 8 WAE. While both seed size and edamame cultivar influence early-season crop competitive ability, the magnitude of these factors on CT and WSA underscores the importance of considering them not as stand-alone tactics but rather as useful additions to a more comprehensive integrated weed management system.

Wheat, Field Pea, and Canola Response to Glyphosate and AMPA Soil Residues

The tripling of glyphosate use in the Canadian prairies during the past decade has raised concerns over the possible accumulation of glyphosate and its main metabolite AMPA in soil over time and whether there could be any detrimental effects on crop production. A controlled environment study was conducted at two locations in Alberta, Canada, to determine glyphosate and AMPA soil concentrations that would injure wheat, field pea, and canola. Treatments included glyphosate acid or AMPA applied at 0, 10, 25, 100, 250, and 500 mg kg−1soil. Shoot and root biomass determinations 8 wk after emergence (WAE) indicated that shoot and root biomass of all crops progressively declined with increasing soil concentrations of glyphosate at both locations. In contrast, AMPA reduced crop shoot and root biomass at only one of two sites. Estimated soil concentrations of glyphosate causing 20% reductions in shoot and root biomass ranged from 80 to 190, 90 to 350, and 120 to 320 mg kg−1for field pea, canola, and wheat, respectively. Soil concentrations of AMPA causing 20% crop biomass reductions ranged from 40 to 70, 20 to 30, and 80 to 120 mg kg−1for field pea, canola, and wheat, respectively. Although substantial crop injury occurred in this study, it must be noted that these rates are very high in terms of field application rates that would be required to achieve these soil concentrations. Doses causing crop injury would convert to estimated glyphosate field rates ranging from 17.6 to 77 kg ha−1. Overall results indicate that even with frequent high-dose glyphosate applications over several years, the likelihood of wheat, field pea, and canola injury from soil residues is low. Nevertheless, there may be merit in greater monitoring of glyphosate and AMPA soil residues in cropping systems with high glyphosate utilization over a long time period.

Halosulfuron Tank-Mixes Applied PRE in White Bean

White bean tolerance and weed control were examined by applying halosulfuron alone or in combination with pendimethalin, dimethenamid-P, orS-metolachlor applied PRE. All herbicides applied alone or in combination caused less than 3% visible injury 1 and 4 wk after emergence (WAE). Halosulfuron applied PRE provided greater than 95% control of common lambsquarters, wild mustard, redroot pigweed, and common ragweed and less than 55% control of green foxtail at 4 and 8 WAE. Weed density and dry weight at 8 WAE paralleled the control ratings. Dry bean yields in halosulfuron plus a soil applied grass herbicide did not differ compared to the weed-free control. Green foxtail competition with halosulfuron PRE applied alone resulted in reduced white bean yield compared to the weed-free control.

Examining the plant-back interval for glyphosate/glufosinate-resistant corn after the application of ACCase inhibitors

Field experiments in 2013 and 2014 examined corn (Zea mays L.) tolerance to acetyl-coenzyme A carboxylase (ACCase) inhibiting herbicides in a scenario where they would have been used to terminate a failed corn stand prior to replanting. To simulate this, herbicides were applied 1 wk or 1 d preplant (PP) and several parameters were measured. Corn injury 1, 2, 4, or 8 wk after emergence (WAE) was similar to the untreated control, regardless of herbicide, rate, or PP application timing. Across herbicides and rates, PP timing did not affect plant stand and aboveground biomass 2 WAE, plant height 4 WAE, or yield. Across application timings, plant stand and aboveground biomass were similar to the untreated control, regardless of herbicide treatment or rate; however, some herbicides reduced height and (or) yield. For example, compared with the untreated control, fluazifop-p-butyl (75 and 150 g ha−1) and sethoxydim (300 g ha−1) each reduced height by about 3%, while clethodim (30 and 60 g ha−1), fluazifop-p-butyl (150 g ha−1), and quizalofop-p-ethyl (72 g ha−1) each reduced yield by about 2%. Therefore, in situations where a grower may need to terminate a failed corn stand, the selection of ACCase-inhibiting herbicides could be based on efficacy rather than plant-back restrictions.

Soybean (Glycine max) cultivar tolerance to saflufenacil

Miller, R. T., Soltani, N., Robinson, D. E., Kraus, T. E. and Sikkema, P. H. 2012. Soybean (Glycine max) cultivar tolerance to saflufenacil. Can. J. Plant Sci. 92: 1319–1328. Six field studies were conducted over a 2-yr period (2009 and 2010) at three Ontario locations to determine the sensitivity of 12 glyphosate-resistant soybean cultivars to saflufenacil applied preemergence (PRE). The level of crop injury was dependent on environmental conditions shortly after application. When soybean emergence was delayed due to cool, wet conditions following planting, 52 and 59 g a.i. ha−1 of saflufenacil resulted in 10% injury 1 wk after emergence (WAE) in cultivars OAC Hanover and RCAT Matrix, respectively. In the other environments, greater than 200 g a.i. ha−1 of saflufenacil was required to induce the same level of injury at 1 WAE. Injury decreased with time; however, the more sensitive soybean cultivars were unable to recover from early-season injury sustained under adverse environmental conditions. A hydroponic bioassay was developed to screen differences in soybean tolerance to saflufenacil. OAC Hanover was more sensitive than all the other cultivars in both field and hydroponic testing (P<0.05). OAC Hanover yield was reduced regardless of environmental conditions. Under cool, wet conditions, 22 g a.i. ha−1 of saflufenacil resulted in a 10% yield reduction, while 46 g a.i. ha−1 was needed under warm dry conditions. All other cultivars required between 82 and 146 g a.i. ha−1 to obtain the same level of yield reduction. This research demonstrates that there is a difference in soybean cultivar sensitivity to saflufenacil applied PRE.

Growth, Development, and Morphological Differences among Native and Nonnative Prickly Nightshades (Solanumspp.) of the Southeastern United States

Prickly nightshades are troublesome weeds of natural habitats, pastures, feedlots, right-of-ways, and croplands. Native and nonnative invasive weedy species of prickly nightshades were compared to determine growth, development, and morphological differences. Six (Solanum bahamense, Solanum capsicoides, Solanum carolinense, Solanum dimidiatum, Solanum donianum, andSolanum pumilum) of the 18 species of prickly nightshades studied are native to the US. Two species,Solanum citrullifoliumandSolanum rostratum, are annuals; the others are perennials or are short lived perennials or annuals in northern extremes of their range in North America. Tables were developed from new and existing data to differentiate vegetative and reproductive characteristics among 18 species of prickly nightshade found in the southeastern US. In greenhouse experiments, average plant height ranged from 24 and 26 cm (9.45 and 10.24 inch) forS. carolinenseandSolanum jamaicense, respectively, to 100 and 105 cm forSolanum tampicenseandSolanum sisymbriifolium, respectively at 10 wk after emergence (WAE). By 10 WAE, the average number of leaves per plant ranged from < 10 forS. carolinenseandSolanum torvumto > 40 leaves/plant forS. rostratumandS. dimidiatum. Average number of nodes/plant main stem ranged from 11, 12, and 14 nodes inS. jamaicense, S. torvum, andS. carolinense, respectively, to 54 nodes inS. rostratum. Average plant dry weights were collected at 10 WAE and were greatest forSolanum mammosumand (> 17 g/plant) (0.6001 oz/plant) and least forS. carolinense(1 g/plant). Based on these data, nightshade growth rate and dry weight were variable among some species and variability may be a result of phenology and life cycles, annual or perennial. Plants ofS. rostratum, an annual, were relatively tall and produced high number of nodes and leaves and had the shortest period from emergence to flower among the prickly nightshades evaluated.

Weed management in cranberry bean with linuron

Soltani, N., Nurse, R. E., Shropshire, C. and Sikkema, P. H. 2011. Weed management in cranberry bean with linuron. Can. J. Plant Sci. 91: 881–888. Field studies were conducted at the Huron Research Station near Exeter, Ontario, in 2006 to 2009 to determine if the sequential application of trifluralin plus imazethapyr applied preplant incorporated (PPI) followed by linuron applied pre-emergence (PRE) at various doses can be used as an effective weed management strategy in cranberry bean production. There was minimal crop injury (6% or less) with various herbicides evaluated at 1 and 4 wk after emergence (WAE). Trifluralin plus imazethapyr applied PPI provided 97 to 100% control of common lambsquarters, 100% control of redroot pigweed, 99 to 100% control of wild mustard, 93 to 100% control of common ragweed, and 97 to 100% control of green foxtail. Linuron applied PRE provided 11 to 100% control of common lambsquarters, 90 to 100% control of redroot pigweed, 78 to 100% control of wild mustard, 71 to 100% control of common ragweed, and 20 to 100% control of green foxtail. The sequential application of trifluralin plus imazethapyr applied PPI followed by linuron applied PRE at various doses provided 100% control of common lambsquarters, 100% control of redroot pigweed, 100% control of wild mustard, 96 to 100% control of common ragweed, and 97 to 100% control of green foxtail. Weed density and shoot dry weight correlated well with the level of weed control. All of the herbicide treatments evaluated increased cranberry bean yield compared with the weedy control. Based on these results the sequential application of imazethapyr plus trifluralin applied PPI followed by linuron applied PRE at 1000 and 2500 g a.i. ha−1 provides a safe and efficacious weed management strategy in cranberry bean production.

Control of volunteer adzuki bean (Vigna angularis) with pre- and postemergence herbicides in corn (Zea mays)

Volunteer adzuki bean within a corn crop can decrease corn yield and increase the adzuki bean seed bank. The objective of this research was to evaluate the efficacy of various preemergence (PRE) and postemergence (POST) herbicides for the control of volunteer adzuki bean [Vigna angularis (Willd.) Ohwi & Ohashi] in corn. Trials were conducted at two locations in 2005, 2006, 2007 and 2009. Experiments were arranged in a randomized complete block design with either seven PRE or ten POST herbicides. Volunteer adzuki bean interference resulted in corn yield losses of 16 to 43%. The PRE herbicides provided variable control. The highest and most consistent control PRE was provided by dicamba/atrazine, which provided 69 to 97% control of volunteer adzuki bean at 4 and 8 wk after emergence (WAE), respectively. Dicamba/atrazine PRE reduced volunteer adzuki bean density and biomass 67 to 97% 10 WAE. Generally, the POST herbicides evaluated provided better and more consistent control of volunteer adzuki bean than the PRE herbicides. Dicamba/atrazine applied POST provided greater than 95% control of volunteer adzuki bean and consistently reduced volunteer adzuki bean density and biomass to the equivalent of the weed-free control. Dicamba/atrazine applied POST resulted in corn yields equivalent to the weed-free control. The best option for controlling volunteer adzuki bean in corn is to apply dicamba/atrazine POST, while the remaining herbicides evaluated provided variable control.

Control of common cocklebur (Xanthium strumarium L.) in corn

Nine field trials (five with PRE and four with POST herbicides) were conducted in 2006 to 2009 on various Ontario farms with heavy common cocklebur infestations to determine the effectiveness of PRE and POST herbicides for the control of common cocklebur in corn. There was no commercially significant corn injury from the PRE herbicides evaluated. Saflufenacil, saflufenacil/dimethenamid-p, isoxaflutole + atrazine, mesotrione + atrazine and dicamba/atrazine, applied PRE provided 85, 85, 76, 73 and 67% control of common cocklebur in corn 8 wk after emergence (WAE), respectively. Common cocklebur shoot dry weight was reduced 84, 80, 79, 75 and 68% with saflufenacil/dimethenamid-p, isoxaflutole + atrazine, mesotrione + atrazine, saflufenacil and dicamba/atrazine, respectively. There was no effect on corn yield compared with the weedy control with the PRE herbicides evaluated. The application of 2,4-D/atrazine POST resulted in unacceptable injury (28%) in corn. Dicamba/atrazine, dicamba/diflufenzopyr, dicamba and mesotrione + atrazine provided up to 98, 95, 90 and 90% control of common cocklebur 8 wk after application (WAA), respectively. All POST herbicide treatments increased corn yield compared with the non-treated control. Saflufenacil and saflufenacil/dimethenamid-p applied PRE and dicamba, dicamba/diflufenzopyr, dicamba/atrazine or mesotrione + atrazine applied POST have potential to provide good to excellent control of common cocklebur in corn under Ontario environmental conditions.

Spread, Growth Parameters, and Reproductive Potential for Brown Flatsedge (Cyperus fuscus)

AbstractBrown flatsedge (Cyperus fuscus) is widely distributed in Europe, Asia, the Indian subcontinent, and the Mediterranean region of Northern Africa. It was apparently introduced into North America in the late 1800s and has steadily moved southward and westward. Brown flatsedge is reported new to Arkansas and Mississippi herewith. Field observations from early spring until frost were made between 2003 and 2007 from populations present at three sites: Chicot County, Arkansas, and Pearl River and Washington counties, Mississippi. Under natural field conditions, brown flatsedge plants germinated from late March and early April until frost. Inflorescences were observed in mid-May and seed production continued until frost. In field populations, the average numbers of scales per spikelet, inflorescences per plant, and spikelets per inflorescence were 15, 28, and 33, respectively. Greenhouse experiments were established in 2008 at Stoneville, MS, to determine growth parameters and the reproductive potential of brown flatsedge. In greenhouse experiments, by 10 wk after emergence (WAE), brown flatsedge plants were 30.2 cm tall and 63.9 cm in diameter, and dry weights were 1.4, 1.0, 2.0, 0.5, and 1.9 g for roots, culms, leaves, bracts, and inflorescences, respectively. Brown flatsedge culms and inflorescences appeared 5 WAE, and by 9 WAE all plants were producing seed. Brown flatsedge could pose a threat to natural plant communities and rice agriculture in Arkansas, Louisiana, Mississippi, Missouri, Tennessee, and Texas. Additional research is needed to determine seed longevity and ecological range potential, and to develop inexpensive and effective control methods.

Weed Management in Single- vs. Twin-Row Cotton (Gossypium hirsutum)

Research was conducted to determine the effect of planting pattern, plant density, and levels of weed management intensity on intercepted photosynthetically active radiation (IPAR), weed control, and cotton lint yield in glyphosate-resistant cotton. Twin-row planting pattern canopy IPAR was 55% 7 wk after emergence (WAE) and 76% 9 WAE compared to 48% for single-row planting pattern 7 WAE and 59% 9 WAE. Regardless of cotton density, row spacing, or weed management intensity, control of browntop millet and Florida beggarweed was at least 88% 18 WAE. Benghal dayflower, sicklepod, and smallflower morningglory control was greater in twin-rows compared to single-rows at a cotton density of 7 plants m−2. Control of Benghal dayflower and sicklepod increased when cotton density increased at low weed management intensities; however, cotton density had no effect on weed control at higher levels of weed management input. At a cotton plant density of 7 plants m−2, twin-row cotton yielded 220 kg ha−1more than the single-row planting pattern. Data indicates twin-row cotton production is feasible and that control of various weeds was better in twin-row than single-row pattern at lower cotton density and weed management intensity.

Leaf Harvesting Time and Frequency Affect Vegetative and Grain Yield of Cowpea

Cowpea [Vigna unguiculata (L.) Walp.] is a vital component of traditional cropping systems in the subtropics and tropics, grown both for high‐protein grain and nutritious fresh leaves. The objectives of this study were to determine the effects of (i) cropping regime and (ii) leaf harvesting initiation time and frequency on yield and yield components of dual‐purpose cowpea. Studies were conducted at the Kenya National Dry land Research Center–Katumani over four seasons. Cowpea cultivar ‘K80’ was grown as a monocrop or intercropped with maize. Leaf harvesting was initiated at 2, 3, or 4 wk after emergence (WAE) and thereafter done at 7‐ or 14‐d intervals. Control plants remained intact with no leaf harvesting. The number of lateral stems per plant, pods per plant, seeds per pod, unit seed weight, and vegetable and grain yields were monitored throughout each season, and plant productivity was found to be lower in intercropped than in monocropped cowpea. Leaf harvesting reduced all yield components. Initiating leaf harvesting at 3 and 4 WAE resulted in the highest leaf and grain yields, respectively. Harvesting leaves at a 7‐d interval was associated with higher leaf yield, while a 14‐d interval led to higher grain yield. Overall, yields were highest under treatments with no leaf harvest and lowest when leaf harvesting was initiated 2 WAE. Results of this study can help dual‐purpose cowpea growers optimize yields according to their production goals.

Response of dry bean to preplant incorporated and preemergence applications of pyroxasulfone

Three field trials were conducted over a 2-yr period at Exeter (2007, 2008) and Ridgetown (2007), Ontario to evaluate the tolerance of two market classes and two cultivars of each market class (cranberry, Etna and Hooter; kidney, Red Kanner and Red Hawk) of dry bean to preplant incorporated (PPI) and preemergence (PRE) applications of pyroxasulfone at 209 and 418 g a.i. ha-1. All treatments including the non-treated control were maintained weed free during the growing season. There was greater injury when pyroxasulfone was applied PPI than PRE, and injury was greater with the high rate at 1, 2, and 4 wk after emergence (WAE). Pyroxasulfone at 209 and 418 g a.i. ha-1 caused as much as 32 and 61% visible injury when applied PPI and 15 and 30% visible injury when applied PRE in dry bean, respectively. Pyroxasulfone at 209 and 418 g a.i. ha-1 decreased shoot dry weight as much as 60 and 80% when applied PPI and 30 and 50% when applied PRE in dry bean, respectively. Plant height was not affected by pyroxasulfone application timing, but was rate dependent. Height was reduced 14, 13, 22 and 13% at 209 g a.i. ha-1 and 24, 31, 42 and 27% at 418 g a.i. ha-1 for Etna, Hooter, Red Kanner and Red Hawk cultivars, respectively. Dry bean yield was reduced as much as 29% at 209 g a.i. ha-1 and 45% at 418 g a.i. ha-1. This research shows that there is not an adequate margin of crop safety for pyroxasulfone applied PPI or PRE at the rates evaluated in Etna, Hooter, Red Kanner and Red Hawk dry beans in Ontario.Key words: Cranberry bean, Etna bean, kidney bean, Hooter bean, Phaseolus vulgaris L., Red Hawk bean, Red Kanner bean, pyroxasulfone