Weed Management Programs Research Articles

Evaluation of Thiencarbazone-methyl– and Isoxaflutole-Based Herbicide Programs in Corn

Field studies were conducted in Louisiana and Mississippi in 2009 and 2010 to evaluate PRE herbicide treatments containing isoxaflutole or a prepackaged mixture of thiencarbazone-methyl : isoxaflutole (TCM : isoxaflutole) for weed control in corn. PRE treatments included the premix of TCM : isoxaflutole alone (30 : 80 g ai ha−1) and with atrazine (1,120 g ai ha−1), isoxaflutole alone (90 g ai ha−1) and with atrazine (1,120 g ai ha−1), and the premix of atrazine plus S-metolachlor (1,820 plus 1,410 g ai ha−1). POST treatments included glufosinate (450 g ai ha−1) or glyphosate (870 g ae ha−1) applied to 30-cm corn along with a no POST treatment. All PRE treatments controlled barnyardgrass, entireleaf morningglory, rhizomatous johnsongrass, Palmer amaranth, and velvetleaf 87 to 95% 4 wk after planting (WAP) and browntop millet and hophornbeam copperleaf were controlled 86 to 95% 8 WAP. Weed control was improved 8 and 20 WAP when either POST treatment was applied. TCM : isoxaflutole plus atrazine controlled barnyardgrass, entireleaf morningglory, Palmer amaranth, and velvetleaf at least 90% 20 WAP regardless of POST treatment. TCM : isoxaflutole plus atrazine provided greater control of browntop millet (90%) than isoxaflutole alone or with atrazine and atrazine plus S-metolachlor where control was 86% 20 WAP. Pooled across POST treatments, all PRE treatments containing isoxaflutole or TCM : isoxaflutole controlled rhizomatous johnsongrass better (74 to 76%) than atrazine plus S-metolachlor (67%). Corn yield following herbicide treatments ranged from 9,280 to 11,040 kg ha−1 compared with 9,110 kg ha−1 for the nontreated. Results indicate that TCM : isoxaflutole or isoxaflutole PRE is an option for use in a corn weed management program and may prolong the use of atrazine where weed resistance may be an issue. Where rhizomatous johnsongrass is a problem, TCM : isoxaflutole or isoxaflutole PRE can provide better control than atrazine plus S-metolachlor PRE. Without PRE treatments, glufosinate or glyphosate was needed for season-long weed control.

Pre and postemergence herbicides for weed control in castor crop

Weed management is among the main factors limiting cultivation of castor (Ricinus communis) in extensive fields, particularly when labor is scarce or expensive. This experiment evaluated the efficiency of weed management programs using preemergence (clomazone, pendimethalin, and trifluralin) and a postemergence herbicide (chlorimuron-ethyl) applied at 20 days after emergence in castor plants cv. BRS Energia under rainfed conditions in Apodi, Brazil. No phytotoxicity was observed on the castor plants, and the postemergence herbicide significantly increased castor seed yield to 1466kgha−1 complementing the weed control of preemergence herbicides treatments in which seed yield was 1207kgha−1. Seed yield on weedy and weed-free treatments was 760 and 1971kgha−1, respectively. Weeds were kept under a satisfactory control up to 40 days after emergence. This program resulted in reasonable weed control because the preemergence herbicides controled monocotyledon weeds, while the postemergence herbicide controlled broad leafed species being selective to castor plants.

Allelopathic Effects of Winter Legumes on Germination and Seedling Indicators of Various Summer Cereals

In the present study, the putative allelopathic potential of aqueous extracts (10 % w/v) of three legumes, i.e. alfalfa, berseem and brassica spp., including distilled water treatments as check were evaluated on germination and early seedling growth indicators of rice, sorghum and millet under laboratory conditions. The treatments were compared in completely randomized design with factorial arrangements in four replications. The recorded observations clearly indicated that the germination process and seedling growth of receptor plants were negatively affected in the presence of legume extracts. The extract of Brassica had the strongtest inhibitory effect on germination process in form of increased mean germination time (MGT) and lowered the coefficient of velocity of germination (CVG), germination % age and germination index (GI) as compared to other extracts. Likewise, the lowest root and shoot length, their fresh and dry weight was also noted in petri dishes with Brassica extracts. Among the receptor crops, rice was the most susceptible in term of both seedling growth and germination attributes. The interaction between test crops and legume extracts was found to be significant for most of studied parameters except germination % age, fresh and dry weight of root and shoot. The presence of allelochemicals in the studied legumes entitled them to be used in weed management programme and is also signal for designing specific production technologies able to reduce their effects on succeeding crops.

Weed Control, Environmental Impact and Profitability of Weed Management Strategies in Glyphosate-Resistant Corn

Eleven field trials were conducted over a three-year period (2006-2008) at three locations in southwestern Ontario, Canada to evaluate the effect of various weed management strategies in glyphosate-tolerant corn on weed control, crop injury, corn yield, environmental impact and profit margin. No visible injury resulted from the herbicide treatments evaluated. Overall, the effect of all factors assessed were location specific. By 56 days after treatment, depending on location, glyphosate applied at the 7 - 8 leaf stage (LPOST), preemergence (PRE) herbicides followed by (fb) glyphosate LPOST and sequential glyphosate applications (EPOST (3 - 4 leaf stage) followed by LPOST) provided more consistent control of annual broadleaf weeds and annual grasses compared to glyphosate applied alone EPOST. Weed control at 56 days after treatment was lower when glyphosate was applied alone LPOST compared to sequential applications of glyphosate or PRE herbicides fb glyphosate. There were no differences in corn yield among the sequential programs evaluated; however, a yield benefit was found when a sequential program was used compared to glyphosate applied alone LPOST. Among the sequential programs the lowest environmental impact was isoxaflutole/atrazine fb glyphosate. The lowest profit margins were associated with atrazine, S-metolachlor/atrazine/benoxacor, dicamba/atrazine and glyphosate LPOST treatments compared to all other treatments. Overall, profit margins tended to be somewhat higher for treatments that included glyphosate applications. Based on these results, the most efficacious and profitable weed management program in corn was a sequential application of glyphosate; however, isoxaflutole/atrazine fb glyphosate was the treatment with the lowest environmental risk while also adding glyphosate stewardship benefits.

Comparison of Weed Management Programs for Furrow-Irrigated and Flooded Hybrid Rice Production in Arkansas

Whether season-long weed control can be achieved in a furrow-irrigated rice system with similar herbicide inputs to that of a flooded system is not known. Field experiments were conducted in 2007 and 2008 at Pine Tree, AR to evaluate different herbicide programs on the weed control efficacy and rice grain yield in furrow-irrigated and flooded rice production systems. Six herbicide programs were evaluated with and without additional late-season “as-needed” herbicide treatments. Minor injury to rice was noted for quinclorac plus propanil. However, the injury was transient and the plants fully recovered. Overall weed control was greater in the flooded system compared with the furrow-irrigated system (up to 20% greater), because flooding effectively prevented the emergence of most terrestrial weeds. In addition, rice grain yields were 13 to 14% greater in flooded compared with furrow-irrigated plots. Irrespective of the irrigation system, herbicide programs that contained a PRE-applied herbicide provided greater weed control and resulted in greater yield compared with those that did not contain PRE-applied herbicide, indicative of the importance of early-season weed control in achieving higher grain yields. On the basis of weed control, yield, and weed treatment cost, the herbicide program with clomazone PRE followed by propanil at four- to five-leaf rice was more efficient than other programs evaluated in both irrigation systems. However, furrow-irrigated plots required as-needed herbicide applications, which were applied after the four- to five-leaf rice stage when two or more plots within a program exhibited ≤ 80% control for any of the weed species. This suggests that furrow-irrigated rice production demands additional weed management efforts and thereby increases production costs. There is also a possibility for substantial yield reduction in the furrow-irrigated system compared with the flooded system. Nevertheless, furrow-irrigated rice production can still be a viable option under water-limiting situations and under certain topographic conditions.

Chemical characterization and allelopathic potential of volatile oil of Eucalyptus tereticornis against Amaranthus viridis

The present study investigated the chemical composition and allelopathic potential of volatile oil from Eucalyptus tereticornis on growth and establishment of Amaranthus viridis, a wasteland weed. The volatile oil was rich in monoterpenoids and a total of 34 components were identified by gas chromatography/gas chromatography–mass spectroscopy analyses, constituting 98.52%. α-Pinene (32.5%) and 1,8-cineole (22.4%) were the two major constituents. The volatile oil and two major components were evaluated for their allelopathic potential against A. viridis. A significant reduction in early seedling growth and seedling vigor of A. viridis was observed in response to volatile oil or its major monoterpenes. Further, the contents of photosynthetic pigments, i.e. chlorophylls a and b, and carotenoids, and cellular respiration in oil-/monoterpene-treated seedlings were significantly reduced thereby indicating adverse effects of the oil on photosynthetic machinery and energy metabolism. Based on the study, it can be concluded volatile oil of E. tereticornis possess allelopathic potential and could be explored as bioherbicide for future weed management programs.

Economic implications of herbicide resistance and high labour costs for management of annual barnyardgrass ( Echinochloa crus-galli) in Philippine rice farming systems

Implications of increasing labour costs and the development of herbicide resistance for profitable weed management in Philippine rice farming systems are investigated. The study employs RIMPhil (Resistance and Integrated Management in the Philippines), a bioeconomic simulation model developed to provide a comprehensive assessment of integrated weed management programmes for the control of annual barnyardgrass ( Echinochloa crus-galli) in rice crops. Results indicate that herbicide application will become increasingly economically attractive, relative to manual weeding, as labour cost increases. This is important since urban migration in the Philippines continues to increase the scarcity of rural labour. Results also show that the onset of herbicide resistance results in substantial losses in farm profit. It is worthwhile for farmers to take management actions to prevent or delay the onset of herbicide resistance, provided that these changes are effective and not too costly. The study highlights the complexity of decision making about integrated weed management on rice farms in the Philippines.

Tank Mix of Saflufenacil with Glyphosate and Pendimethalin for Broad-spectrum Weed Control in Florida Citrus

Citrus (Citrus spp.) is one of the most important crops in Florida agriculture. Weed control is a major component in citrus production practices. If not controlled, weeds may compete with citrus trees for nutrients, water, and light and may also increase pest problems. Herbicides are an important component of integrated weed management program in citrus. Saflufenacil, a new herbicide registered for broadleaf weed control in citrus, can be applied alone or in a tank mix with other herbicides to improve weed control efficacy. A total of six field experiments were conducted in 2008 and 2009 to evaluate the efficacy of saflufenacil applied alone or in a tank mix with glyphosate and pendimethalin for weed control. In addition, experiments were also conducted to evaluate phytotoxicity of saflufenacil applied at different rates and time intervals in citrus. The results suggested that saflufenacil applied alone was usually effective for early season broadleaf weed control; however, weed control efficacy reduced beyond 30 days after treatment (DAT) compared with a tank mix of saflufenacil, glyphosate, and pendimethalin. For example, control of weeds was ≤70% when saflufenacil or glyphosate applied alone compared with tank mix treatments at 60 and 90 DAT. Addition of pendimethalin as a tank mix partner usually resulted in better residual weed control compared with a tank mix of saflufenacil and glyphosate, and this herbicide mixture was comparable with grower's adopted standard treatment of a tank mix of glyphosate, norflurazon, and diuron and several other tank mix treatments. Saflufenacil applied once in a season at different rates or even in sequential applications did not injure citrus trees when applied according to label directions. It is concluded that with its novel mode of action, saflufenacil tank mixed with glyphosate and pendimethalin would provide citrus growers with another chemical tool to control broadleaf and grass weeds.

Predicted Soybean Yield Loss As Affected by Emergence Time of Mixed-Species Weed Communities

Potential crop yield loss due to early-season weed competition is an important risk associated with postemergence weed management programs. WeedSOFT is a weed management decision support system that has the potential to greatly reduce such risk. Previous research has shown that weed emergence time can greatly affect the accuracy of corn yield loss predictions by WeedSOFT, but our understanding of its predictive accuracy for soybean yield loss as affected by weed emergence time is limited. We conducted experiments at several sites across the Midwestern United States to assess accuracy of WeedSOFT predictions of soybean yield loss associated with mixed-species weed communities established at emergence (VE), cotyledon (VC), first-node (V1), or third-node (V3) soybean. Weed communities across research sites consisted mostly of annual grass species and moderately competitive annual broadleaf species. Soybean yield loss occurred in seven of nine site-years for weed communities established at VE soybean, four site-years for weed communities established at VC soybean, and one site-year for weed communities established at V1 soybean. No soybean yield loss was associated with weed communities established at the V3 stage. Nonlinear regression analyses of predicted and observed soybean yield data pooled over site-years showed that predicted yields were less than observed yields at all soybean growth stages, indicating overestimation of soybean yield loss. Pearson correlation analyses indicated that yield loss functions overestimated the competitive ability of high densities of giant and yellow foxtail with soybean, indicating that adjustments to competitive index values or yield loss function parameters for these species may improve soybean yield loss prediction accuracy and increase the usefulness of WeedSOFT as a weed management decision support system.

Cultivar-specific Weed Management Programs for ‘Russet Burbank’ and ‘Bannock Russet’ Potato Production in Wisconsin

Field trials were conducted at Hancock, WI, in 2008 and 2009 to determine reduced-herbicide weed management programs for ‘Russet Burbank’ and ‘Bannock Russet’ potato (Solanum tuberosum) based on cultivars’ developmental characteristics. Six treatments applied to each cultivar included: preemergence (PRE) broadcast s-metolachlor and metribuzin (the industry standard); PRE in-row banded s-metolachlor and metribuzin with cultivation at 15% canopy development; postemergence (POST) broadcast rimsulfuron and metribuzin; POST between-row banded glyphosate; POST in-row banded rimsulfuron and metribuzin with cultivation at 15% canopy development; and cultivation alone at 15% canopy development. In 2008 and 2009, for both cultivars, visual assessments indicated weed suppression was reduced when glyphosate was POST between-row banded, compared with other treatments, and weed suppression was consistently high when rimsulfuron and metribuzin were POST broadcast. As expected, in-row weed control was consistently poor when glyphosate was between-row POST banded, providing no in-row weed control. Regardless of cultivar or year, in-row weed control was comparable to or better than the industry standard when herbicides were broadcast or in-row banded with cultivation at 15% canopy development. Potato yield was poor when glyphosate was POST between-row banded and when cultivation was used without herbicide application. Yield was consistently high when herbicides were POST broadcast, which provided no reduction in treated area from the industry standard of PRE broadcast. In both years, ‘Russet Burbank’ yield was greatest when herbicides were POST in-row banded with cultivation at 15% canopy development; ‘Bannock Russet’ yield was greatest when herbicides were PRE in-row banded with cultivation at 15% canopy development. Cultivar-appropriate weed management systems that band herbicides over the crop row in combination with cultivation would provide a two-thirds decrease in herbicide application from the industry standard without risk of yield loss.

Comparative Efficacy of Different Weed Management Strategies in Wheat

Weed management programs should focus on environmental safety along with benefits to the farmer. We evaluated the effects of various weed control methods: ?daab? practice (stale seed bed technique), manual hoeing, and the chemical method (mixture of Buctril Super 60EC [bromoxynil + MCPA] 0.45 kg ai ha-1 and Puma Super 75EW [fenoxaprop-P-ethyl] 0.75 kg ai ha-1) in combination with different planting geometries: 22.5 cm apart single row, 22.5 cm apart crisscross double row, 30 cm apart single row and broadcast sowings on weed control and grain yield of spring wheat (Triticum aestivum L.) var. Sehar 2006 at the University College of Agriculture, University of Sargodha, Pakistan, during the winters of 2009 and 2010. The chemical method, manual hoeing and ?daab? practice gave 71.44%, 30.69% and 28.60% weed controls resulting in 11.79%, 11.09% and 4.95% increases in grain yield above that of the weedy control, respectively. The 22.5 cm apart single row sowing in combination with chemical weed control proved to be the best regarding weed control (87.23%), grain yield (4073 kg ha-1) and number of fertile tillers m-2 (509.5), whereas wheat plant height (108.2 cm), number of grains spike-1 (45.90) and 1000 grain weight (45.23 g) were higher in 30 cm apart single row sowing in interaction with manual hoeing. Grain yield showed a significant negative (b = -152.8) and positive (b = 3.21) correlation with weed biomass and fertile tillers m-2, respectively. Chemical weed control, ?daab? practice and manual hoeing gave cost:benefit ratios of 2.50, 1.95 and 1.14, respectively. Although the chemical method seems the most profitable, the ?daab? practice was found to be the most advantageous if environmental concerns were taken into consideration.

Weed Management with Glyphosate- and Glufosinate-Based Systems in PHY 485 WRF Cotton

Glyphosate-resistant (GR) Palmer amaranth has become a serious pest in parts of the Cotton Belt. Some GR cotton cultivars also contain the WideStrike™ insect resistance trait, which confers tolerance to glufosinate. Use of glufosinate-based management systems in such cultivars could be an option for managing GR Palmer amaranth. The objective of this study was to evaluate crop tolerance and weed control with glyphosate-based and glufosinate-based systems in PHY 485 WRF cotton. The North Carolina field experiment compared glyphosate and glufosinate alone and in mixtures applied twice before four- to six-leaf cotton. Additional treatments included glyphosate and glufosinate mixed withS-metolachlor or pyrithiobac applied to one- to two-leaf cotton followed by glyphosate or glufosinate alone on four- to six-leaf cotton. All treatments received a residual lay-by application. Excellent weed control was observed from all treatments on most weed species. Glyphosate was more effective than glufosinate on glyphosate-susceptible (GS) Palmer amaranth and annual grasses, while glufosinate was more effective on GR Palmer amaranth. Annual grass and GS Palmer amaranth control by glyphosate plus glufosinate was often less than control by glyphosate alone but similar to or greater than control by glufosinate alone, while mixtures were more effective than either herbicide alone on GR Palmer amaranth. Glufosinate caused minor and transient injury to the crop, but no differences in cotton yield or fiber quality were noted. This research demonstrates glufosinate can be applied early in the season to PHY 485 WRF cotton without concern for significant adverse effects on the crop. Although glufosinate is often less effective than glyphosate on GS Palmer amaranth, GR Palmer amaranth can be controlled with well-timed applications of glufosinate. Use of glufosinate in cultivars with the WideStrike trait could fill a significant void in current weed management programs for GR Palmer amaranth in cotton.

Allelochemicals identified from Jerusalem artichoke ( Helianthus tuberosus L.) residues and their potential inhibitory activity in the field and laboratory

Weed management systems often seek biological solutions to minimize the environmental impacts related to the use of herbicides in agricultural systems. The suppressive effects of allelochemicals can sometimes be used effectively to provide biological pest and weed control. Jerusalem artichoke ( Helianthus tuberosus L.) has been reported to be a highly invasive weed in European cropping systems, but this plant is also gaining interest as a cultivated crop in Italy. The aim of this study was to investigate the impact of Jerusalem artichoke and its extracts upon the germination and growth of seedling weeds and crops. HPLC coupled to MS was used for identification of the compounds associated with the observed growth inhibition. The weed suppressive activity of local biotypes of Jerusalem artichoke on weed growth and establishment was also evaluated in a field experiment. Shoot extracts of the cultivar Fuseau were consistently most inhibitory to germination and seedling growth of lettuce, particularly the diethyl ether extract. Solvent partitioning of the aqueous extracts of dried artichoke shoots resulted in greater inhibition in comparison to the aqueous extract itself. The diethyl ether extract provided 2-fold greater growth inhibition, in comparison to the aqueous extract, at concentrations of less than 0.5 mg extract per Petri dish. HPLC MS evaluation of the diethyl ether extract led to the identification of salicylic acid ( o-hydroxybenzoic acid), and the closely related compound p-hydroxybenzaldehyde, as well as minor quantities of o-coumarinic acid and coumarin in the active fraction inhibiting lettuce seedling growth. Field observations provided further evidence for the allelopathic potential of H. tuberosus residues, as significant weed growth inhibition was observed in Jerusalem artichoke-infested plots with soil-incorporated residues in comparison to non-infested field sites, both in terms of weed seedling emergence and growth. The allelopathic potential of H. tuberosus may be of interest in the implementation of integrated weed management programmes by considering the suppressive ability of this plant and its residues for weed management in the field.

Benchmark study on glyphosate‐resistant cropping systems in the United States. Part 5: Effects of glyphosate‐based weed management programs on farm‐level profitability

Glyphosate-resistant (GR) crops have changed the way growers manage weeds and implement control strategies. Since the introduction of GR crops, growers in many instances have relied on glyphosate almost exclusively to control a broad spectrum of weeds. This over-reliance on glyphosate has resulted in the evolution of glyphosate resistance in some weed species. Growers and scientists are concerned about the sustainability of GR crops and glyphosate. When a grower is making decisions about weed control strategies, economic costs and benefits of the program are primary criteria for selection and implementation. Studies across six states were initiated in 2006 to compare the economics of using a weed resistance best management practice (BMP) system with a grower's standard production system. Resistance BMP systems recommended by university scientists were more costly but provided similar yields and economic returns. Rotation of GR crops resulted in a higher net return (maize and soybean) compared with continuous GR crop (cotton or soybean) or rotating a GR crop with a non-GR crop (maize). Growers can implement weed resistance BMP systems with the confidence that their net returns will be equivalent in the short run, and, in the long term, resistance BMP systems will prevent or delay the evolution of GR weeds in their fields, resulting in substantial savings.

Benchmark study on glyphosate‐resistant cropping systems in the United States. Part 1: Introduction to 2006–2008

Glyphosate-resistant (GR) crop technology has dramatically impacted agriculture. The adoption of GR systems in canola, maize, cotton, soybean and sugar beets has been widespread in the United States. However, weed scientists are concerned that growers' current herbicide programs and weed management tactics will affect their sustainability and effectiveness. Without proper management, the potential for weed populations to express a high degree of resistance to glyphosate will adversely impact the utility of glyphosate. In 2005, weed scientists from six universities initiated a long-term research study to assess the sustainability of GR technology. This paper introduces five other articles in this series. Over 150 fields of at least 10 ha were selected to participate in a long-term field-scale study, and each field was split in half. On one-half the grower continued using the current weed management program; on the other half the grower used academic-recommended herbicide resistance best management practices. Field data were collected in 2006-2008 to determine the impact of the two weed management programs on weed populations, diversity, seedbank, crop yields and economic returns. This long-term study will provide invaluable data for determining the sustainability and profitability of diversified weed management programs designed to lower the risk of evolving weed resistance to glyphosate.

Weed resistance development and management in herbicide-tolerant crops: experiences from the USA

The evolution of weeds in USA agroecosystems predates herbicide tolerant (HT) crops by several decades. However, given the unprecedented adoption of genetically engineered (GE) HT crops, particularly in maize, cotton and soybean and the concomitant use of glyphosate, the evolution of glyphosate-resistant (GR) biotypes of agronomic important weeds now represents a significant threat to the sustainability of the GE HT trait and the herbicide. Notably, GR biotypes of horseweed (Conyza canadensis), common waterhemp (Amaranthus tuberculatus), Palmer pigweed (Amaranthus palmeri), giant ragweed (Ambrosia trifida) and johnsongrass (Sorghum halepense) have increased dramatically in frequency in conjunction with the adoption of crop production systems based on GE HT crops. Furthermore, other shifts in weed communities have been observed. It must be emphasized that the GE HT crops did not directly cause these weed shifts. The industry was responsible initially for these changes in weed communities given their initial positions that the glyphosate-resistant weed problems were unlikely to evolve and the recommendations to use glyphosate exclusively for weed management. However, decisions by growers to use glyphosate must be factored in as imparting selection pressure on the weed communities resulting in weed management problems, particularly when university recommendations strongly suggested not to use glyphosate in this manner. The key is now to provide growers with sufficient information to convince them to adopt integrated weed management programs and utilize best management practices. Given the presumed and real benefits of convenience and simplicity of the GE HT crop production systems; this will be a difficult task.

Site-Specific Weed Management in Cotton Using WebHADSS™

Field trials were established in 2005 and continued in 2006 to evaluate a conventional broadcast herbicide sprayer compared to a variable spray (sensor-activated) weed-sensing sprayer (WSS). The computer-based Herbicide Application Decision Support System (WebHADSS™) was used to determine a portion of the herbicides applied (based on herbicide efficacy and economics). Weed control, herbicide usage, crop yield, and net returns were compared across treatments. The broadcast applications were usually the most effective at controlling weeds. A PPI herbicide did not always improve weed control compared to treatments in which no PPI herbicide was applied. Variable treatments used less herbicide than the broadcast system in both years. Cotton lint yields in broadcast applications were similar to the weed-free check in both years of the study. Variable treatments often provided equivalent net returns (gross yield revenue less weed control cost) to the broadcast treatments. Although herbicide savings were observed in the variable treatments when compared to a broadcast system, a reduction in weed control was observed, indicating the need for future improvements of this system. A site-specific weed management program used in conjunction with WebHADSS™ may have potential in cotton production systems in the Texas Southern High Plains where weed densities are low.

Evaluation of Cereal and Brassicaceae Cover Crops in Conservation-Tillage, Enhanced, Glyphosate-Resistant Cotton

Research was conducted for 2 yr at Marianna, AR, to determine whether the fall-planted cover crops rye, wheat, turnip, and a blend of brown and white mustard (Caliente) would aid weed management programs in conservation-tilled, enhanced, glyphosate-resistant cotton. Wheat and rye easily were established both years and turnip and mustard blend stands were better in the second year. The cover crops alone were more suppressive of Palmer amaranth, pitted morningglory, and goosegrass in 2007 than in 2008. Rye was generally superior to wheat in suppressing the three evaluated weeds. Once herbicides were applied, there were seldom differences among cover crops for a particular herbicide program as a result of the highly efficacious herbicide programs. Cotton yields were not affected by wheat, rye, or the mustard blend, but yields were lowest in plots that followed turnip both years, possibly because of allelopathy. Integration of cover crops, especially cereals, into conservation-tilled, glyphosate-resistant cotton aided early-season weed management and could reduce the selection of glyphosate for herbicide resistance.

A pilot weed management programme for batwing passion flower in New Zealand

Passiflora apetala (batwing passion flower) was introduced as an ornamental variety in the mid1990s and has been dispersed in New Zealand through the activities of subtropical plant collectors and avian vectors Although P apetala is currently restricted to the Northland and Auckland regions of the North Island some closely related Passiflora species have become serious weeds in New Zealand A pilot weed management programme was implemented to undertake intensive surveillance and organism management of all P apetala plants to significantly reduce the rate of naturalisation at two sites a heavily infested rural site and an urban/residential location The objectives of the management programme were to assess the feasibility effectiveness and costs of local elimination attempts and to inform partners of future management options for this species

Growth Stage Influenced Sorghum Response to Broadcast Flaming: Effects on Yield and Its Components

There is an increasing interest among organic producers to grow grain sorghum [Sorghum bicolor (L.) Moench] under organic crop production systems and propane flaming could be part of an integrated weed management program. Therefore, the objective of this study was to investigate the response of sorghum to broadcast flaming as influenced by propane dose and crop growth stage. Field experiments were conducted at the Haskell Agricultural Laboratory of the University of Nebraska, Concord, NE in 2008 and 2009 using five propane doses applied at three growth stages that included 3‐leaf (V3), 5‐leaf (V5), and 7‐leaf (V7). The propane doses evaluated were 0, 13, 24, 44, and 85 kg ha−1 and were applied using a custom‐built (ATV mounted) research flamer driven at a constant speed of 6.4 km h−1 Crop response to propane doses was described by using log‐logistic models on the basis of visual estimates of crop injury, various yield components (plants m−2, heads plant−1, kernels head−1, and 1000‐kernel weight), and grain yield. Sorghum response to flaming varied among crop growth stages and propane doses. Based on the evaluated parameters, sorghum flamed at V5 and V7stages showed higher tolerance compared to V3 stage. The maximum yield reductions with the highest propane dose of 85 kg ha−1 were 11, 6, and 9% for V3, V5, and V7 stages, respectively. In addition, propane doses that resulted in a 5% yield loss were 13, 72, and 46 kg ha−1 for V3, V5, and V7 stages, respectively, indicating that plants flamed at V5 or V7 stage can tolerate higher dose of propane for the same yield reduction compared to V3 stage. Flaming has a potential to be used effectively in organic sorghum production if properly used.