Molecular characterization,vector identification and partial host range determination of phytoplasmas associated with faba bean phyllody in Iran

During surveys of phytoplasma diseases, faba bean phyllody (FBP) was observed in several locations in Fars and Bushehr provinces (southern Iran). Samples of affected plants from Borazjan (Bushehr province) and Fasa (Fars province) were used to transmit the phyllody agent to faba bean, mung bean, pea, alfalfa and periwinkle by grafting, dodder and/or vector insect. Orosius albicinctus (Distant) was identified as the vector of Borazjan (BFBP) and Fasa (FFBP) faba bean phyllody. Naturally affected faba bean plants and all inoculated plants were positive for phytoplasma by direct PCR using the P1/P7 primer pair and nested PCR using P1/P7 and R16F2n/R16R2 primer pairs. Sequencing of PCR products identified the associated phytoplasmas as members of 16SrII phytoplasma group. Phylogenetic analysis using full length 16S rRNA gene sequences also confirmed similarity of the BFBP and FFBP phytoplasmas to the 16SrII group phytoplasmas. In this analysis the FFBP phytoplasma was grouped with ’Candidatus Phytoplasma australasia’, representative of 16SrII-D subgroup, while the BFBP phytoplasma formed a discrete group close to the 16SrII-C subgroup. Restriction fragment length polymorphism (RFLP) confirmed that BFBP and FFBP phytoplasmas belong to 16SrII group. Virtual RFLP confirmed that as members of peanut witches’ broom (16SrII) phytoplasma group, BFBP and FFBP phytoplasmas belonged to 16SrII-C and16SrII-D subgroups, respectively. Phytoplasmas associated with BFBP and FFBP were shown to be serologically related to the Fars alfalfa witches’broom phytoplasma, a member of 16SrII-C subgroup. It seems that witches’broom affected alfalfa fields are natural reservoirs of the FBP phytoplasma in southern Iran.     

Devastation of sesame (Sesamum indicum L.) crops in different agroclimatic zones of India by genetically diverse subgroups of phytoplasma

The sesame crop is highly susceptible to infection by phytoplasmas, a class of cell wall-less plant pathogenic bacteria (Mollicutes), which is responsible for widespread loss of sesame crops in both North and South India in recent years. Therefore, characterizing the pathogen population is required before the control measures can be devised and implemented. With molecular tools based on nested polymerase chain reaction (PCR) assays, sequencing, restriction profiling, and phylogenetic analysis, phyllody-affected sesame plants collected from nine different states of India were found to be infected by phytoplasmas belonging to two 16Sr groups, namely 16SrI and II. Two subgroups of phytoplasma −16SrI-B and 16SrII-D— were prevalent in symptomatic sesame samples collected from North India, whereas phytoplasma of only the 16SrII group was found in South India. However, the latter samples were diverse, belonging to three different subgroups (16SrII-A, II-C, and II-D). In addition, yearly phyllody-affected sesame samples from Delhi for 4 consecutive years (2007–2010) showed variation in the infecting phytoplasma: the subgroup 16SrII-D was detected in samples collected in 2007, and 16SrI-B was predominantly found in the samples collected in the subsequent years. The study also provides molecular evidence for the association between 16SrI-B phytoplasma and different symptoms in sesame crops such as fasciation, little leaf, and stunting. This is the first study to report the association of the phytoplasma subgroups 16SrII-A and II-D with sesame crops in India. This study provides a baseline for designing specific detection and molecular analysis strategies for quarantine purposes. It also highlights the need for examining the dynamics of seasonal or location-specific variation in vector populations to determine the pattern of infection outbreaks.     

Identification and molecular characterization of phytoplasmas and rickettsia pathogens associated with ‘Bunchy Top Symptom’ (BTS) and ‘Papaya Bunchy Top’ (PBT) of papaya in Cuba

Two different papaya diseases have been previously reported in Cuba, Bunchy Top Symptom (BTS) associated with a phytoplasma of group 16SrII ‘Candidatus Phytoplasma aurantifolia’ and Papaya Bunchy Top (PBT), associated with a rickettsia. Regarding the regional phytosanitary impact of both diseases for the papaya crop, the present study investigated the occurrence of BTS and PBT in papaya fields in Cuba, and the possible mixed infection of phytoplasma and rickettsia pathogens associated. Papaya plants showing symptoms of BTS or PBT or both, were collected in Las Tunas and Havana provinces from January 2009 to February 2010, and evaluated for phytoplasma and rickettsia by PCR with primers targeting the 16S ribosomal RNA and the rickettsial succinate deshydrogenase (sdhA) genes, respectively. Phytoplasmas and rickettsia were individually detected in 76/86 BTS-symptomatic and 22/22 PBT-symptomatic papaya plants, and simultaneously detected in 5/86 (5.81%) of the BTS-symptomatic and 17/22 (77.27%) of the PBT-symptomatic plants. Conventional and virtual RFLP analyses of the 16S rDNA sequences revealed the presence of phytoplasmas of group 16SrI ‘Candidatus Phytoplasma asteris’ and 16SrII in papaya plants affected by BTS and PBT, and identified two new phytoplasma subgroups, 16SrI-X and 16SrII-N in papayas fields of Las Tunas, which was confirmed by phylogenetic analysis. The partial rickettsia sdhA gene sequences were 100% identical to that of the rickettsia associated with PBT in Puerto Rico. Results confirm that phytoplasmas are consistently associated with both BTS and PBT symptoms, and that mixed infections of phytoplasma and rickettsia pathogens can occur in either BTS or PBT-affected papaya fields, which implies new epidemiological constraints for the disease control.     

Occurrence of ‘Candidatus Phytoplasma asteris’ in citrus showing Huanglongbing symptoms in Mexico

Huanglongbing (HLB), one of the most devastating citrus diseases in the world, was detected in Mexico in 2009. Currently, HLB is associated with the bacteria Candidatus Liberibacter spp., although several phytoplasmas have been found from trees showing HLB-like symptoms in Brazil and China. The aim of this study was thus to determine if, in addition to ‘Ca. L. asiaticus’ (CLas), phytoplasma species are also associated with HLB-like symptoms in citrus groves of Mexico. Citrus plants exhibiting symptoms such as diffuse chlorosis, blotchy mottle and vein yellowing were collected in the Mexican States of Nayarit, Colima and Sinaloa between August 2011 and September 2012. Samples were then evaluated for phytoplasmas and CLas by PCR, using primers that respectively target the genes for the 16S ribosomal RNA and 50S ribosomal protein of the β operon (rplA-rplJ). Out of 86 HLB-symptomatic citrus plants, 54 were positive for CLas, 20 were positive for phytoplasmas, 7 were found in mixed infections with both pathogens and 19 samples were negative for CLas and phytoplasmas. Actual and virtual RFLP analyses of the 16S rDNA sequences enabled us to classify two HLB phytoplasma strains as members of the aster yellows group (16SrI) ‘Candidatus Phytoplasma asteris’, which was confirmed by phylogenetic analysis. The HLB phytoplasma strain identified from Nayarit (HLBpc-Nay-IB) belongs to subgroup B (16SrI-B), and the strains identified from Colima (HLBpc-Col-IS) and Sinaloa (HLBpc-Sin-IS) belong to subgroup S (16SrI-S). The partial ‘Ca. L. asiaticus’ rplA-rplJ gene sequences were 100% identical to the ‘Ca. L. asiaticus’ strains isolated from several countries affected by HLB. These results confirm the association of ‘Candidatus Phytoplasma asteris’ with HLB-like symptoms in citrus groves in Mexico. Nonetheless, further studies are required to fully describe the ‘Ca. L. asiaticus’ and ‘Ca. P. asteris’ interactions in citrus, which will greatly assist the design of efficient management strategies.     

The incidence of stolbur disease and associated yield losses in vegetable crops in South Moravia (Czech Republic)

The study was performed at a vegetable farm from 2006 to 2008 in the intensive horticultural area of Lednice (South Moravia, Czech Republic), where a stolbur (phytoplasma) epidemic had occurred. The study showed that the incidence of stolbur disease reached 15% in both tomato (Lycopersicon esculentum) and pepper (Capsicum annuum), and up to 6.7% in celeriac (Apium graveolens). There were significant yield losses in the stolbur-affected plants; total yield losses were up to 60% in tomato, 93% in pepper, and 100% in celeriac. The mean yield was significantly decreased in stolbur-affected plants, compared to healthy plants (i.e. from 42.79 to 17.21 fruits per plant in tomatoes; from 10.11 to 0.74 fruits per plant in peppers). In the locality studied, it was mainly the weed plants Convolvulus arvensis and Cirsium arvense (which were frequently interspersed among the crops), which tested positive for the stolbur phytoplasma and might have provided a reservoir for the phytoplasma infection.     

Critical competition period of parthenium weed (Parthenium hysterophorus L.) in maize

For minimizing yield losses due to infestation of a weed, it is essential to know about its critical period of competition in a specific crop. The yield response of maize (Zea mays L.) to different competition periods (0, 35, 42, 49 and 56 days after crop emergence (DAE), and competition throughout growing season) of the invasive weed Parthenium hysterophorus L. was tested during autumn seasons of two consecutive years 2012 and 2013. Increasing parthenium competition period increased its dry weight up to 448% and relative competition index up to 52%. The corresponding increases in the uptake of N (up to 581%), P (up to 700%) and K (up to 669%) were also recorded. Parthenium weed competition period of 35 DAE decreased grain yield and harvest index of maize. However, number of grains and grain weight per cob, and 100-grain weight of maize were reduced at parthenium weed competition period beyond 42 and 56 DAE, respectively. Maize grain yield losses varied between 21 and 53% with parthenium competition period ranging from 35 DAE to full growing season. Maximum N, P, and K uptake by parthenium was 18.4, 2.4 and 17.7 kg ha⁻¹, respectively. A three parameter logistic model was fitted to yield data in response to increasing durations of weed infestation. The critical timing of parthenium weed removal to avoid 5% and 10% maize grain yield loss was 8 and 17, and 13 and 23 DAE during year 2012 and 2013, respectively. Relatively shorter critical period of parthenium weed competition in maize crop suggested this weed to be highly allelopathic in addition to its competitive behavior.     

野茼蒿变叶病病原物的分子鉴定

利用植原体16S rDNA通用引物R16mF2/R16mR1对海南表现变叶症状的野茼蒿样品总DNA进行PCR扩增,获得约1.4 kb的特异片段,并对扩增产物进行核苷酸序列测定。通过BLAST程序比较、系统进化树构建及iPhy Classifier分析表明,海南发生的野茼蒿变叶植原体在分类上属于花生丛枝植原体组中的A亚组,即16Sr II-A亚组。这是我国首次在野茼蒿上发现植原体病害。     

Identification of a phytoplasma associated with pomegranate little leaf disease in Iran

During 2012–2014 surveys for the presence of phytoplasma diseases in Fars province (Iran), pomegranate little leaf symptoms were observed in several orchards in Khafr and Neyriz areas. Samples collected from symptomatic plants positively reacted in nested PCR assays using P1/P7 followed by R16F2n/R16R2 primer pairs producing the expected 1,250 bp DNA fragments. Real and virtual RFLP analysis showed that the sequences of phytoplasma strains from Khafr and Neyriz (KPLL and NPLL strains, respectively) were identical to each other and belong to 16SrII phytoplasma group, subgroup D. Phylogenetic analysis of the R16F2n⁄R16R2 DNA region confirmed that KPLL and NPLL phytoplasmas were enclosed in the same clade as other 16SrII-D subgroup phytoplasmas. This is the first reported occurrence of a 16SrII phytoplasma infecting pomegranate trees.     

海南槟榔黄化病病原物的分子鉴定

槟榔黄化病是槟榔上的一种重要病害,如何快速检测该病原菌是防治该病的重要基础。利用植原体16SrDNA通用引物对海南感染黄化病的槟榔花苞总DNA进行巢式PCR扩增,获得约1.2kb的特异片段,并对扩增产物进行核苷酸序列测定。通过BLAST程序比较、系统进化树构建及iPhyClassifier分析表明,引起海南槟榔黄化病病原植原体属于翠菊黄化植原体组(16SrⅠ组),且为该组中一个新的亚组,即G亚组,现将其暂命名槟榔黄化植原体(Arecanut yellow leaf phytoplasma,AYL)。     

苦楝丛枝病植原体海南株系SecY基因序列分析及亚组分类

利用植原体16SrⅠ组通用引物对secYF1／secYR1,应用PCR技术从采白海南省儋州地区的表现典型丛枝症状的苦楝植株总DNA中扩增到约1．4kb的特异片段,将此片段克隆后进行序列测定,序列分析及系统关系树构建的结果表明,该片段长1358bp,苦楝丛枝病海南株系（Chinaberry witches＇-broom phytoplasma strain Hainan,CWB-Hn）与玉米丛矮（Maize bushy sttmt,MBS）植原体聚类在同一条进化枝上;AluⅠ,MseⅠ和Tsp509Ⅰ这3种酶的电子酶切图谱表明,CWB-Hn与MBS的酶切图谱一致,故初步判定苦楝丛枝病植原体海南株系属于secY-L亚组,在亚组水平上进一步明确了苦楝丛枝病植原体海南株系的分类地位。     

Can winter cover crops influence weed density and diversity in a reduced tillage vegetable system?

Weeds are a major constraint for organic crop production. Previous research has found that cover crops in reduced tillage systems can provide weed interference, subsequently reducing inputs and improving crop yield. However, questions remain about effects of cover crop species identity and cover crop biomass on weed suppression and crop yield. This four-year study investigated how winter cover crops grown alone or in mixture influenced weed presence and crop yield in a reduced tillage organic vegetable system. Treatments were barley (Hordeum vulgare L.), crimson clover (Trifolium incarnatum L.), mixed barley + crimson clover, and a no-cover crop control. Plots were flail-mowed and strip-tilled prior to planting main crops (2011 and 2012: broccoli Brassica oleracea L.; 2013 and 2014: crookneck squash Cucurbita pepo L.). We measured density, diversity, and community composition of weeds and viable weed seeds, changes in weed percent cover within growing seasons, and crop yield. We found that the presence of barley, crimson clover, or barley + crimson clover reduced weed density by 50% relative to the control. Cover crop biomass negatively influenced weed density and weed seed diversity, and positively influenced squash yield. Weed percent cover within growing seasons did not respond differentially to cover crop treatment. Cover crop treatment and cover crop biomass had no influence on weed or weed seed community composition. These results suggest that reduced tillage winter cover crops in mixture or monoculture can similarly suppress weeds and improve yield, primarily due to biomass effects.     

Cereal–legume rotations in a Mediterranean environment: biomass and yield production

The effects of various crop rotations on the biomass and yield of barley (Hordeum vulgare L.), faba bean (Vicia faba L.), and pea (Pisum sativum L.) grown under Mediterranean conditions were studied during three growing seasons in the semiarid Spanish Central Plateau. The treatments comprised six crop sequences: barley monoculture, fallow–barley (currently used in the area), faba bean–barley, pea–barley, fallow–barley–faba bean, and fallow–barley–pea. The fallow was of 16-month duration. The site is representative of cultivated areas of the Plateau, and the soil has a loam texture. Results concentrate on barley as the main crop. Season distribution of rainfall restricted the effectiveness of the management practices and in consequence there were few differences between rotations. Barley had greater biomass and yield after fallow than after other crops but significant differences were dependent on year. Legumes, an alternative to fallow, increased land use, permitted alternative weed control measures, and reduced the need for fertiliser. The intensification of the fallow–barley cropping system is best achieved by reducing the frequency of fallow and including other crops of relatively small biomass production, thereby minimising the impact on yield of the succeeding barley crop.     

海南长春花黄化病植原体的DAPI荧光显微检测

对感染黄化病的海南长春花植株，应用DAPI荧光显微技术对其嫩茎和叶柄进行了切片染色观察，结果表明：在感病植株的韧皮部筛管分子中存在大量特异性的植原体DNA荧光光点，而在健康植株的筛管分子则未发现有特异性的植原体荧光。另对其茎和叶柄中的植原体含量进行比较，结果显示茎中的含量要比叶柄中稍高。     

海南槟榔黄化植原体分子检测及其系统发育关系研究

由植原体引起的槟榔黄化病是海南特色经济作物槟榔种植上的一种毁灭性病害。本研究通过PCR扩增测序、序列多重比对和系统发育分析,对海南部分代表性地区槟榔致死性病原植原体的序列信息与系统发育关系进行检测分析。结果表明：本研究检测的保亭、屯昌、万宁等海南部分代表性地区的槟榔黄化植原体的16S rDNA序列一致;BLAST分析表明各株系16S rDNA与16SrI组植原体同源性为100%。序列多重比对分析表明,本研究各槟榔黄化植原体株系与海南苦棟丛枝、长春花绿变、马松子变叶、辣椒黄化皱缩、蛇婆子丛枝、细圆藤丛枝和日本洋葱黄化、美国翠菊黄化等植原体同源性为100%;与已报道的海南万宁、印度、海南三亚的槟榔黄化植原体16S rDNA序列同源性分别为99.9%、99.9%、99.8%。系统发育分析表明,本研究槟榔黄化植原体与海南苦棟丛枝、长春花绿变、马松子变叶、辣椒黄化皱缩、蛇婆子丛枝、细圆藤丛枝等株系聚于一个分枝,支持率为100%。此外,在发病槟榔叶片、花穗、心叶等组织部位均可检测到植原体。研究结果表明,海南槟榔黄化植原体与海南苦棟丛枝、长春花绿变、马松子变叶、辣椒黄化皱缩、蛇婆子丛枝、细圆藤丛枝等植原体株系的同源性极高,槟榔黄化病很可能会以这些寄主植物作为病原传播载体进行传播扩散。     

Activity of benzothiadiazole on chrysanthemum yellows phytoplasma (‘Candidatus Phytoplasma asteris’) infection in daisy plants

A commercial preparation of the plant resistance elicitor benzothiadiazole (BTH) (Bion, Syngenta Crop Protection) was tested for its capacity to induce systemic resistance against chrysanthemum yellow phytoplasma (CYP) infection in the Chrysanthemum carinatum plant. Following one 2.4 mM BTH application, plants were exposed to CYP-infective Macrosteles quadripunctulatus leafhoppers. Symptom development and phytoplasma multiplication in the test plants were measured over time. BTH application delayed symptom development and phytoplasma multiplication in treated plants compared with the control ones. CYP titre and symptom severity were significantly lower for the first two weeks post-inoculation in treated plants compared with the control ones, suggesting that systemic acquired resistance (SAR) induced by BTH in C. carinatum is temporary. Higher concentrations of BTH resulted in phytotoxic effects involving the whitening of apical leaves. BTH application was ineffective in reducing the transmission efficiency of CYP by its leafhopper vector. Actually, in both single and group transmission tests, the proportion of infected plants was similar among BTH-treated and untreated plants. The survival of M. quadripunctulatus was unaffected by feeding on BTH-treated daisy plants. Moreover, when leafhoppers were allowed to choose between treated and untreated plants, they showed no preference. We conclude that SAR induced in daisy plants by BTH has no detrimental effects on the vector leafhopper. If the activity of BTH against phytoplasmas is confirmed also on other phytoplasma/host–plant associations, BTH applications might be included in new, more environmentally friendly, integrated management strategies of phytoplasmoses.     

Weed emergence as affected by maize (Zea mays L.)-cover crop rotations in contrasting arable soils of Zimbabwe under conservation agriculture

Weed control in smallholder farming systems of sub-Saharan Africa is labour intensive or costly. Many researchers have therefore advocated for the use of cover crops in weed management as an affordable alternative for smallholders. Cover crops may be grown in rotations to suppress weeds and reduce the reliance on herbicides. The use of cover crops creates microenvironments that are either conducive or inhibitive to the emergence of certain weed species. A study, initiated in 2008 in contrasting soils at four different locations of Zimbabwe, investigated the effect of maize (Zea mays L.)-cover crop rotations on the emergence of weeds that showed dominance in those soils. Weed assessments were however, carried out from 2011 to 2014. The weed species Galinsoga parviflora Cav., Commelina benghalensis L., and Richardia scabra L. showed dominance in all four locations with weed densities as high as 500 plants m⁻² being recorded for R. scabra L. in a sandy soil. Maize-cover crop rotations resulted in higher densities of Bidens pilosa compared with maize monocropping (control treatment) due to its high nitrogen (N) requirement to produce more seeds. On the other hand, the integration of cover crops such as pigeon pea [Cajanus cajan (L.) Millsp.] that had poor shading qualities, due to large gaps or spaces and slower initial growth, had limited effects on competitive weeds such as Cyperus esculentus L. which tend to dominate exhausted soils. The density of C. esculentus was 38% greater in maize–pigeon pea rotations compared with the control treatment. Variability between seasons and sites affected emergence of all weeds in the present study, which masked long-term trends. The results suggest that there is need to identify the germination and emergence requirements of specific weeds and select cover crops best suitable for their control. The study provides useful information for farmers and advisors on the best cover crops for control of certain problematic weeds in different soil types of Zimbabwe.     

Discrimination of sterile oat (Avena sterilis) in winter barley (Hordeum vulgare) using QuickBird satellite images

Site-specific weed management implies detecting the location of weeds in order to generate maps of their spatial distribution. This information facilitates a more accurate application of herbicides, spraying them in the exact areas of weed growth and in the required doses. In order to explore the potential of commercial satellites to discriminate and map weeds, we used the information contained in high spatial resolution images acquired by the QuickBird satellite to assess the density of sterile oat (Avena sterilis) present in a winter barley field at two different dates (March and June). Our results confirmed the potential of using satellite images in the spectral discrimination of weed patches in infested fields. The results of binary logistic regressions showed that the best matches in the classification of three categories (low, medium, or high sterile oat densities) corresponded to the March image. QuickBird’s March image provided reliable estimates of sterile oat patches in barley crops when weed density was relatively high (between 86% and 94% of agreement between predicted and observed densities). However, when weed densities were lower than 10 plants/m² there were serious difficulties to distinguish them from weed-free zones (between 72 and 75% of global agreement in the classification) with large underestimation of medium density weed patches (10 plants/m²). This is a potential limitation considering than the thresholds used for herbicide application decisions are generally close to this density. However, the information obtained may still be useful for producing field maps to describe the spatial distribution of this weed. Moreover, these studies have provided valuable information on the best spectral regions and/or vegetation indices for approaching discrimination between sterile oat and cereal crops and the most suitable period for it.     

Gramineous and non-gramineous weed species as alternative hosts of Fusarium graminearum,causal agent of Fusarium head blight of wheat,in Argentina

Weeds and wild plants around and within crops could serve as alternative hosts of fungal pathogens. In this work we describe the isolation of Fusarium graminearum, the main causal agent of Fusarium head blight (FHB) in Argentina from the inflorescences of healthy weed plants belonging to sixty seven gramineous and non-gramineous species, which showed no symptoms of Fusarium infection, sampled throughout a year. Fifty four of the weed species considered, belonging to 19 botanical families, were first identified as alternative hosts of F. graminearum in the present work. Furthermore, the trichothecene chemotype of a group of isolates was analysed and strains belonging to 15-acetyldeoxynivalenol, 3-acetyldeoxynivalenol and nivalenol chemotypes were found. The information provided could prove valuable to study further the epidemiological role of weeds in FHB epidemics, which might help to improve management of the disease in wheat growing areas.     

海南长春花变叶病病原物的分子鉴定

本研究分别利用植原体16S rDNA和核糖体蛋白(ribosomal protein,rp)基因的通用引物对自然表现变叶症状的海南长春花样品总DNA进行PCR扩增,获得16S rDNA基因片段长为1 432 bp,rp基因片段长为1 211 bp。BLAST程序比较、系统进化树构建及iPhyClassifier分析表明:海南长春花变叶病是由植原体引起的,该植原体株系属于16S rⅠ-B亚组,与候选种Ca.Phytoplasma asteris相关,将其暂命名为长春花变叶病植原体海南株系(Periwinkle phyllody strain Hainan,PP-Hn)。     

Weed control,environmental impact and profitability with trifluralin plus reduced doses of imazethapyr in dry bean

Field experiments were conducted in 2003, 2006, and 2007 in Ontario to determine if reduced doses of imazethapyr combined with trifluralin applied pre-plant incorporated (PPI) can be used as an economically and environmentally feasible weed management strategy for broad spectrum weed control in white and kidney bean. There was minimal injury (<5%) in white or kidney bean from imazethapyr applied alone or in combination with trifluralin, regardless of dose. The dose of imazethapyr required for 80 and 95% control of Setaria viridis (L.) Beauv. (green foxtail), Chenopodium album L. (common lambsquarters) and Ambrosia artemisiifolia L. (common ragweed) was reduced when combined with trifluralin (600 g ai ha⁻¹). There was a trend for increased yield of white and kidney bean with increasing doses of imazethapyr applied alone and in combination with trifluralin. Combining trifluralin with imazethapyr increased the environmental impact (EI) by more than ten-fold compared to imazethapyr alone. The lowest dose of imazethapyr used in this study resulted in the lowest environmental risk. The doses of imazethapyr that maximized profit were 38 g ai ha⁻¹ for white bean and 47 g ai ha⁻¹ for kidney bean. Combining imazethapyr with trifluralin will provide growers with a weed management strategy that provides acceptable weed control, with only a small increase in environmental impact, and has the potential to increase yields and net returns.