Long-term perennial weed control strategies: Economic analyses and yield effect in hazelnut (Corylus avellana)

Weeds limit hazelnut productivity through competition and interference. Field experiments were conducted from spring 2010 through 2013 to evaluate string trimming alone or combined with herbicides in hazelnut orchards to control mugwort (Artemisia vulgaris L.), purple nutsedge (Cyperus rotundus L.), and burning nettle (Urtica urens L.). Treatments were mowing with a string trimmer (ST) alone, or ST followed by glyphosate, glyphosate + diflufenican, and glyphosate + carfentrazone-ethyl. These combinations also were applied with pendimethalin and oxyfluorfen as pre-emergence applications. The experiments were conducted in Fatsa-Ordu, Turkey, on a sandy clay soil with multi-stemmed trees (ocak). The combination treatments improved weed control compared to ST alone. Glyphosate plus carfentrazone-ethyl application 15 days after ST was the most effective treatment for control of these weeds. This combination was more effective in reducing seed bank reserves of A. vulgaris, C. rotundus and U. urens than herbicides applied alone or in mixtures throughout all seasons. Hazelnut yield was not significantly affected by herbicide treatments in 2010 or 2011. Hazelnut yield increased during the latter half of the experimental period, in 2012 and 2013. In a mixed population of A. vulgaris, C. rotundus and U. urens, 89 plants per m² caused 12.1% yield loss. When the density increased to 256 plants per m², yield losses increased to 29.7%. Hazelnut treated with ST followed by glyphosate plus carfentrazone-ethyl had the highest financial return. Post-emergence weed management systems in hazelnut should include ST followed by glyphosate plus carfentrazone-ethyl applications for maximum returns.     

Genetically-modified herbicide-resistant (GMHR) crops a two-edged sword? An Americas perspective on development and effect on weed management

GMHR crops have been cultivated in the Americas for nearly 20 years. Prior to release, regulators asked the question, “will herbicide selection pressure for evolution of HR weeds increase significantly as a result of GMHR crop cultivation?” In hindsight, they could not have imagined the rapid, widespread adoption of glyphosate-resistant (GR) crops and subsequent chain of events: surge in glyphosate usage at the expense of other herbicides, sharp drop in investment in herbicide discovery, unrelenting rise of GR and multiple-HR weed populations, and increasing herbicide use in GMHR cropping systems. In this brief review, we outline grower adoption of GMHR soybean, maize, cotton, and oilseed rape (canola) in the Americas, and their impact on herbicide-use practices for weed management. Cultivars with stacked-HR traits (e.g., glyphosate + glufosinate + dicamba or 2,4-D) will provide a short-term respite from HR weeds, but will perpetuate the chemical treadmill and selection of multiple-HR weeds. The only sustainable solution is for government or end-users of commodities to set herbicide-use reduction targets in our major field crops similar to European Union member states, and include financial incentives or penalties in agricultural programs to support this policy. Concomitantly, industry incentives must expand to improve grower adoption of best management practices for HR weeds. New or emerging technologies will provide additional tools for reactive HR weed management in the future, but their time of arrival is uncertain.     

Herbicide tolerant canola systems and their impact on winter crop rotations

Canola is widely grown in Australia to provide diversity within winter crop rotations. Its production is heavily reliant on triazine tolerant varieties but Clearfield^® and conventional varieties are also significant components of the industry. Glyphosate tolerant varieties have been introduced, thereby providing an alternative technology to be incorporated into the farming systems. To evaluate the potential impact of the relative herbicide technologies, a comparison of herbicide tolerant canola weed management systems was undertaken at Wagga Wagga, Australia over a 5-year rotation. Near isogenic lines of conventional, glyphosate tolerant and triazine tolerant varieties were evaluated for their abilities to control annual ryegrass (Lolium rigidum), the most challenging weed of temperate crops in Australia. Glyphosate tolerant and triazine tolerant canola achieved high levels of ryegrass control and attained higher yields than the conventional system. Glyphosate tolerant canola provided extra control of broadleaf weeds and also achieved better seed oil levels when compared with the other canola systems. There were positive flow-on weed management benefits for the remainder of the crop sequence from the weed control achieved in the initial crop, particularly following glyphosate tolerant canola. Subsequent control of volunteer canola in all treatments was readily achieved by using paraquat/diquat. The glyphosate tolerant weed management system was more profitable than the triazine tolerant system, although no allowance was made for technology costs as they were not known at the time of study. These outcomes demonstrate the potential value of herbicide tolerant canola to Australian farmers.     

Effect of herbicides on weed management in dry-seeded rice sown under different tillage systems

In India, dry-seeded rice (DSR) production systems are rapidly replacing conventional rice production systems due to various advantages. DSR systems can be managed under zero-till (ZT) conditions or after a preparatory tillage, often referred to as conventional tillage systems (CONT). Although previous reports indicate the contribution of tillage to weed suppression, the effect of one-time preparatory tillage in a DSR system could vary depending on the dominant weeds in the system, vertical seed distribution and the weed seed dynamics. A study was conducted to test the efficacy of ZT and CONT and their interaction with herbicide treatments on the weed population dynamics and rice grain yield in 2010 and 2011. Tillage systems did not affect weed emergence, weed biomass, tiller production and crop yield. However, herbicide treatments varied in their efficacy on individual weeds. Hand-weeding treatments and pendimethalin combined with hand weeding did not effectively control Cyperus rotundus L. and Panicum maximum Jacq. (a perennial grass weed with underground parts). The herbicide combination of metsulfuron and chlorimuron was effective in controlling C. rotundus but not grass weeds. This indicates the need for sequential applications of herbicides for grass weed control or integration of hand weeding to achieve broad-spectrum weed control. Apart from hand weeding (three times), treatment with penoxsulam–cyhalofop and pendimethalin followed by (fb) hand weeding resulted in low weed density, high tiller production and grain yield. The study clearly indicates that tillage does not always lead to weed suppression compared with ZT, and herbicides must be chosen based on the dominant weeds in a system. The results of this study are pertinent as herbicide-resistant weeds are rapidly evolving under continuous herbicide selection pressure, which warrants studies on enhancing productivity through low-input, environmentally friendly and sustainable production technology.     

Predicting maize yield in a multiple species competition with Xanthium strumarium and Amaranthus retroflexus: Comparing of approaches to modeling herbicide performance

A modeling approach based on weed relative leaf area (RLA) was used to describe the maize yield affected by weed competition and herbicide dose. The change of early RLA with herbicide dose was described using standard dose–response model. The dose response of individual weed species was included in a multivariate rectangular hyperbolic relationship between maize yield and weed relative leaf-area. Final model satisfactorily described the change of the weed relative leaf areas with herbicide dose in a multiple species competition with maize to reach a reasonable estimate of crop yield. Parameter estimates indicated that the maize yield could be about 11.23 t/ha in the absence of weeds. Applying herbicide at 0.29 rate of the recommended dose could decrease the Amaranthus retroflexus leaf area by 50%. For Xanthium strumarium, increasing the dose up to 0.58 rate of the recommended dose caused 50% reduction in early relative leaf area. The relative leaf area of the X. strumarium was 4.2-fold larger than that of the A. retroflexus at the time of herbicide application. Model validation indicated significantly better predictive ability of the leaf area model than that of the density model. Leaf area model permits to monitor the canopy (with considering the relative ground cover of neighboring plants) and decide that if a competitive crop allows reducing the dose. Recommending the precise required amount of herbicide is achieved using models that account for the interactions among crop and weed species, which survive and persist in the competition after herbicide application.     

Agronomic and economic assessment of intensive pest management of dry bean (Phaseolus vulgaris)

Two common production constraints of dry bean (Phaseolus vulgaris) in Ontario are annual weeds and anthracnose (caused by Colletotrichum lindemuthianum). Dry bean is not considered a competitive crop and weed interference can result in substantial yield losses, while anthracnose is considered one of the most devastating diseases in dry bean production. A study conducted in Ontario Canada, examined the effect of two herbicide programs on weed management, thiamethoxam insecticide treatment on plant enhancement and three fungicide programs on anthracnose development in a navy bean cv. ‘OAC Rex’. The premium herbicide program (s-metolachlor + imazethapyr) reduced percent weed ground cover relative to the economic herbicide program (trifluralin) in five of six locations. Thiamethoxam increased emergence and vigour at only one location, which contradicts reported benefits of thiamethoxam on plant health. The herbicide or thiamethoxam treatments did not affect anthracnose disease severity, visible seed quality, net yield or economic return. The fungicide seed treatment was often superior to the untreated control, for a number of the parameters measured. The application date of the foliar fungicide, relative to the onset of disease, varied between site-years. This dramatically influenced the fungicide’s effectiveness. Foliar fungicides increased seed quality and net economic return compared to the control when applied prior to disease development. The combination of fungicide seed treatment followed by a foliar fungicide provided the largest reduction in anthracnose severity.     

Effect of cover crops and mulches on weed control and nitrogen fertilization in tomato (Lycopersicon esculentum Mill.)

Cover crops and mulches are a suitable choice for sustainable agriculture because they improve weed control and crop performance. The aim of this research was to investigate weed control and nitrogen supply by using different winter cover crop species which were converted into mulches in spring. We carried out a 2-year field experiment where a tomato crop was transplanted into four different types of mulches coming from winter cover crops [hairy vetch (Vicia villosa Roth.), subclover (Trifolium subterraneum L.), oat (Avena sativa L.), and a mixture of hairy vetch/oat)] and in conventional treatment (tilled soil without mulch). The mixture of hairy vetch/oat cover crop produced the highest aboveground biomass (7.9 t ha⁻¹ of DM), while the hairy vetch accumulated the highest N in the aboveground biomass (258 kg N ha⁻¹). The oat cover crop was the most effective cover crop for suppressing weeds (on average −93% of weed aboveground biomass compared to other cover crops). After mowing the cover crop aboveground biomass was placed in strips as dead mulch into which the tomato was transplanted in paired rows. Weed density and total weed aboveground biomass were assessed at 15 and 30 days after tomato transplanting to evaluate the effect of mulches on weed control. All mulches suppressed weeds in density and aboveground biomass compared to the conventional system (on average −80% and −35%, respectively). The oat was the best mulch for weed control but also had a negative effect on the marketable tomato yield (−15% compared to the conventional treatment). Amaranthus retroflexus L. and Chenopodium album L. were typical weeds associated with the conventional treatment while a more heterogeneous weed composition was found in mulched tomato. Legume mulches, in particular hairy vetch, gave the best marketable tomato yield 28% higher than the conventional system both with and without nitrogen fertilization. This research shows that winter cover crops converted into dead mulch in spring could be used successfully in integrated weed management programs to reduce weed infestation in tomato crops.     

Efficacy of a new glyphosate formulation for weed control in maize in southwest Nigeria

A field trial in 2003 and 2004 assessed the efficacy of a new formulation of glyphosate, Touchdown Forte HiTech (glyphosate-TF) and two older versions, Roundup (glyphosate-RP) and Touchdown (glyphosate-TD) for weed control in Nigeria. Treatments were glyphosate-TF at 0.25–1.25 kg a.i./ha, glyphosate-RP at 1.8 kg a.i./ha, and glyphosate-TD at 1.0 kg a.i./ha. Weeded and unweeded treatments were controls. Visual evaluations of weed control at 4 and 8 weeks after treatment (WAT) in both years indicated that glyphosate-TF at all doses gave moderate to complete control of all major weeds (50–100%). At 4 WAT, control of Ageratum conyzoides L., Commelina benghalensis L., Ipomoea involucrata P. Beauv., Brachiaria comota [Hochst ex A. Rich] stapf, and Acalypha ciliata Forssk was at a level similar to that in the weeded control. In 2003, all herbicide formulations and the weeded control reduced Imperata cylindrica (L.) Beauv. shoot dry biomass to the same level at 8 WAT (91–100%) and at maize harvest (83–88%). In 2004, 0.50–1.25 kg a.i./ha of glyphosate-TF and 1.8 kg a.i./ha of glyphosate-RP gave 95% reduction at 8 WAT and 97% at harvest, similar to the weeded control. Maize grain yield in the weeded control and herbicide treatments was 2.8 times higher than that in the unweeded control in both years. These results indicate that glyphosate-TF is effective for weed control in maize at herbicide doses lower than the older formulations.     

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.     

Allelopathic effects of Ambrosia artemisiifolia L. in the invasive process

Ambrosia artemisiifolia (common ragweed), an annual native to North America, is now present in many European countries where it causes summer hay fever and interferes with several important crops. We investigated if common ragweed invasiveness could be explained by its leaf tissue and root exudate allelopathic potential on indicator crops (alfalfa, barley, maize, lettuce, tomato, and wheat), weeds (Echinochloa crus-galli, Solanum nigrum, Portulaca oleracea, and Digitaria sanguinalis), and common ragweed itself in laboratory and greenhouse conditions. Different residue substrates were prepared for soil incorporation and trials were conducted under both laboratory (1, 2, and 3 g residues/Parker dish) and greenhouse conditions (1.28 g residues/pot). The effect of the preparations on the germination and growth of the indicator crops and weeds were evaluated relative to soil previously used to grow A. artemisiifolia. Results showed tomato was the most sensitive indicator crop species as growth was reduced by more than 50% in both laboratory and greenhouse experiments. Lettuce root and shoot growth were also inhibited, but only when common ragweed residues, and not root exudates, were added to the substrate. Among the weeds, E. crus-galli was not affected by common ragweed while D. sanguinalis suffered a large germination reduction (90%) after incorporation of 3 g of residues. If common ragweed occurred as weed in a field, the cultivation of a less sensitive crop such as winter wheat should be considered before the cultivation of a more susceptible crop.     

Tolerance of winter wheat (Triticum aestivum L.) to pre-emergence and post-emergence application of saflufenacil

Saflufenacil is a new herbicide being developed for pre-plant burndown for non-selective removal of broadleaf weeds and pre-emergence (PRE) broadleaf weed control in field crops, including maize, soybean, sorghum and wheat. As part of studying the potential use pattern of this herbicide, four field studies were conducted in 2006 and 2007 at Concord, northeast Nebraska, to determine winter wheat tolerance to PRE and post-emergence (POST) applications of saflufenacil. The fall POST applications were conducted at the 2–3 leaf stage (5 cm height) whereas the spring POST and tank-mixes studies were sprayed at the 4th node stage (40 cm height) of crop. Dose-response curves based on log-logistic model were used to determine the ED (effective dose) values of saflufenacil for visual ratings of crop injury and relative yield. There was no crop injury or yield reduction with PRE applied saflufenacil dose of up to 400 g a.i. ha⁻¹. However, there was significant crop injury in the POST applications in the fall (up to 95%) and in the spring (up to 67%). There was also yield reduction of as much as 66% in the fall and 58% in the spring POST applications. Addition of adjuvants also increased crop injury levels. For example, at 14 days after treatment in the fall applications, about 5% visual crop injury (ED₅) was evident with 82, 67 and 10 g a.i. ha⁻¹ of saflufenacil compared with 51, 30 and 11 g a.i. ha⁻¹ in the spring, with no adjuvant, or non-ionic surfactant (NIS), or crop oil concentrate (COC), respectively. Saflufenacil at half the proposed used dose of 25 g a.i. ha⁻¹ was safe to mix with the currently used POST herbicides of wheat with no visible crop injury and yield reduction. PRE applications of saflufenacil would be safe for use in winter wheat; however, the POST application of saflufenacil alone or with the adjuvant NIS or COC produces unacceptable injury and yield loss. These results are similar to the proposed PRE use pattern of saflufenacil. In addition, the proposed label does not suggest the POST use of saflufenacil in winter wheat, or any other cereal crops, which is similar to what we have concluded from this study.     

Classification of crops and weeds from digital images: A support vector machine approach

In most agricultural systems, one of the major concerns is to reduce the growth of weeds. In most cases, removal of the weed population in agricultural fields involves the application of chemical herbicides, which has had successes in increasing both crop productivity and quality. However, concerns regarding the environmental and economic impacts of excessive herbicide applications have prompted increasing interests in seeking alternative weed control approaches. An automated machine vision system that can distinguish crops and weeds in digital images can be a potentially cost-effective alternative to reduce the excessive use of herbicides. In other words, instead of applying herbicides uniformly on the field, a real-time system can be used by identifying and spraying only the weeds. This paper investigates the use of a machine-learning algorithm called support vector machine (SVM) for the effective classification of crops and weeds in digital images. Our objective is to evaluate if a satisfactory classification rate can be obtained when SVM is used as the classification model in an automated weed control system. In our experiments, a total of fourteen features that characterize crops and weeds in images were tested to find the optimal combination of features that provides the highest classification rate. Analysis of the results reveals that SVM achieves above 97% accuracy over a set of 224 test images. Importantly, there is no misclassification of crops as weeds and vice versa.     

Interseeding a Cover Crop as a Weed Management Tool is More Compatible with Soybean than with Maize in Organic Farming Systems

Abstract

Weeds are the most serious threat to crop production in organic farming systems. Information on the spatial distribution of weeds is important for effective weed management. The objective of this study was to evaluate the effect of the ground cover of the main crops (soybean and maize) and cover crop on the spatial distribution of weeds for two row sections, ‘within the row (IR)’ and ‘between the rows (BR)’. The cover crop was interseeded in BR 3 – 4 weeks after sowing the main crops in two years, and weed density and vegetation cover ratio (VCR, an index of ground cover) of the main crops and cover crop were measured. There was a significant difference in the spatial distribution of weeds between the two main crops. In IR, weed density was higher in maize than in soybean, while in BR, it was higher in soybean. This means that weed suppression in IR was more important for maize, while the suppression in BR was more important for soybean. The negative relationship between VCR of the main crop plus cover crop and weed density in each row section suggests that the difference in ground cover was one of the reasons for the difference in weed density between the two main crops. The cover crop markedly increased the VCR in BR, but only slightly increased VCR in IR in both main crops. These results suggest that the cover crop was more compatible with soybean than with maize, because the high weed density in IR of maize could not be decreased sufficiently by the slight increase of VCR in BR by the cover crop.     

Comparing weed and crop seedling response to pre-emergence pendimethalin application in Corchorus olitorius and Abelmoschus esculentus

Field experiments and bioassay tests were carried out to evaluate the relative response of the crops, tossa jute (Corchorus olitorius L.) and okra [Abelmoschus esculentus (L.) Moench], and their associated weeds to pre-emergence application of pendimethalin at 0.33, 0.66, 0.99, 1.32 kg ai ha⁻¹ and a pendimethalin+atrazine tank mixture at 1.32+2.05 kg ai ha⁻¹. Bioassay tests were carried out using herbicide solutions of corresponding concentrations and herbicide-treated soil. Field application of pendimethalin at 0.66 kg ai ha⁻¹ and the herbicide mixture in both crops effectively controlled most seedling weeds including Rottboellia cochinchinensis. Euphorbia heterophylla and Calopogonium mucunoides, which persisted from 2 weeks after treatment (WAT) were not controlled. Herbicide application during crop establishment markedly inhibited the growth of both seedling weeds and crops. The mixture caused the highest weed and crop injury. Pendimethalin at 0.33 kg ai ha⁻¹ had minimal effect on these crops. Weed growth, weed tolerance of herbicide treatment and crop seedling injury were higher in tossa jute than that in okra, under the conditions of this study. The use of low pendimethalin doses in an integrated weed management system will ensure effective control of seedling weeds, and prevent crop injury and residue accumulation in edible plant produce.     

Weed control in sunn hemp and its ability to suppress weed growth

Sunn hemp is a tropical, herbaceous annual legume that has potential as a cover crop during the summer in temperate climates. Due to the recent increased interest in sunn hemp breeding and seed production for temperate climates, there is a need for weed control in sunn hemp production. No herbicide product currently on the market specifically identifies sunn hemp as a tolerant crop. The aims of this research were 1) to evaluate herbicides with the intent of identifying a herbicide program that can assure near weed free sunn hemp intended for seed harvest and 2) to demonstrate and quantify sunn hemp-weed suppression. Pre-emergence applied treatments consisted of pendimethalin alone, imazethapyr alone, and pendimethalin plus imazethapyr. Pendimethalin alone provided consistent effective weed control and maximum sunn hemp biomass, but when yellow nutsedge was present, imazethapyr was required for effective control and greater sunn hemp biomass. The combination of pendimethalin and imazethapyr was detrimental to sunn hemp biomass yield. Results also established that sunn hemp is tolerant of 2,4-DB applied post-emergence, but was not necessary for weed control in these studies because of the lack of broadleaf weed pressure. In a separate study with variable sunn hemp densities, weed biomass reductions of ≥50% were obtained with sunn hemp densities of only 20 to 50 plants m⁻². This degree of weed suppression obtained from relatively modest sunn hemp densities is likely indicative of the ability of sunn hemp to grow faster and taller than other plants.     

Yield losses of soybean and maize by competition with interseeded cover crops and weeds in organic-based cropping systems

Weed management is a major issue in organic farming systems. Although interseeding cover crops is one alternative to herbicides, cover crops often suppress not only weeds but also main crops. Therefore, using cover crops for weed control without adverse effects on main crop growth is important. To verify the effect of cover crops on competition between main crops, cover crops and weeds in a snowy-cold region, main crops soybean (Glycine max Merr.) in 2005 and maize (Zea mays L.) in 2006 were grown with cover crops winter rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth), respectively. The cover crops were sown on three sowing dates: before main crop planting (Pre-MC), on the same date of main crop planting (Syn-MC) and after main crop planting (Post-MC). A plot without cover crops (Sole-MC) was used as a control. The dry weight (DW), vegetation cover ratio (VCR), vertical community structure and chlorophyll content were measured to estimate the competition between main crops, cover crops and weeds. Weed DW was suppressed significantly by sowing cover crops in both soybean and maize. This weed suppression was associated with the increase of VCR of main crops plus cover crops at the early growth stage of main crops. Soil seed banks of dominant weed also became lower by sowing cover crops, implying the importance of proper weed management for suppressing weeds successively. In addition, the sowing dates of cover crops had large effects on main crops DW especially in maize, i.e., it was significantly lower in Pre-MC and Syn-MC than in Post-MC. Although the cover crop height was markedly shorter than the main crop height, the chlorophyll content of the main crops was significantly lower when cover crops were sown earlier. These results suggest that the growth inhibition of main crops by cover crops was partly caused by competition for nutrients between main crops and cover crops, and this growth inhibition was alleviated when cover crops were sown after the establishment of main crops. Consequently, soybean yield was the highest in Post-MC and decreased by 29%, 18% and 7% in Sole-MC, Pre-MC and Syn-MC, respectively, and maize yield was also the highest in Post-MC and decreased by 68%, 100% and 24% in Sole-MC, Pre-MC and Syn-MC, respectively. It was concluded that weeds could be controlled effectively by sowing cover crops after planting main crops in organic farming systems in a snowy-cold region.     

Control of grassy weeds in annual canarygrass

There are currently no herbicides registered in Argentina for the selective control of grassy weeds in annual canarygrass (Phalaris canariensis L.). The principal grassy weeds are darnel ryegrass (Lolium temulentum L.) and wild oats (Avena fatua L.), which cause grain yield and quality losses. The potential of diclofop-methyl and clordinafop-propargyl for their control was assessed through greenhouse and field trials, in which crop phytotoxicity and weed control efficacy were evaluated. It was found that (i) field application of clordinafop-propargyl resulted in severe crop damage, except for low doses that did not affect the species to be controlled; (ii) although field application of diclofop-methyl resulted in a certain degree of phytotoxicity on wild oats, these effects were insufficient for efficacious control; and (iii) field and greenhouse application of diclofop-methyl between 200 and 500 g a.i. ha⁻¹ revealed differences between crop sensitivity and that of darnel ryegrass. In this range, crop phytotoxicity in the greenhouse was less than 20% compared to more than 60% in the weed, and in the field only slight crop phytotoxicity symptoms were observed. As in the greenhouse, field application resulted in significant phytotoxic effects upon darnel ryegrass, high efficacy levels, a low survival rate amongst treated plants and a notable reduction in seed production by surviving plants. Only the highest dose (500 g a.i. ha⁻¹) in one of the field trials resulted in a significant reduction in crop grain yield. Hence diclofop-methyl application appears to offer a promising means for controlling darnel ryegrass.     

苏北垦区豆田杂草生长为害习性

苏北垦区豆田杂草分属15科,36属,41种,恶性杂草有稗,苍耳等9种。在大豆整个生育期间通常出现1～2个萌发高峰,主要集中在6月中旬～7月下旬。杂草种子于8～10月成熟。种子在土壤中的埋深及出苗期,直接影响杂草的出苗和繁殖。杂草与大豆的相互竞争,以在大豆播种一个月后最为剧烈。0～2cm和6～25cm耕层中贮葳的杂草种子最多。     

异噁唑草酮·噻酮磺隆在玉米不同种植区应用的除草效果和安全性研究

2016～2017年在东北春玉米种植区和黄淮海夏玉米种植区设立田间试验基地,研究除草剂异噁唑草酮·噻酮磺隆悬浮剂在不同区域玉米田播后苗前处理的杀草谱及除草效果、对玉米安全性及对下茬作物生长的影响。结果表明,26.7%异噁唑草酮·噻酮磺隆悬浮剂141.75～283.5 g ai/hm2在玉米播后苗前使用,对东北春玉米种植区主要杂草稗草、狗尾草、藜、反枝苋、苘麻、刺儿菜和黄淮海玉米种植区主要杂草马唐、牛筋草、反枝苋、马齿苋、铁苋菜等禾本科杂草和阔叶杂草均有理想效果,药后40～45 d,异噁唑草酮·噻酮磺隆上述处理对杂草鲜重防效仍在95%左右,可实现一次施药控制玉米全生长期的杂草,在玉米田具有较好的除草增产作用;对后茬播种的小麦、大豆、花生、油菜、菠菜生长无影响。     

Response of weeds and soil microorganisms to imazaquin and pendimethalin in cowpea and soybean

Herbicides applied to combat weeds and increase crop yields may also have undesired effects on beneficial soil microorganisms. Field studies were conducted in 2005 and 2006 in Zaria, Nigeria, to evaluate the response of weeds and soil microorganisms to imazaquin applied at 0.05, 0.10, 0.20 and 0.40 kg a.i./ha and pendimethalin applied at 1.0, 2.0, 4.0, and 8.0 kg a.i./ha in cowpea and soybean. Hoe-weeded and unweeded (no herbicide) plots were controls. Both herbicides significantly reduced weed biomass in both crops, when compared to the unweeded control, which had the highest weed biomass at all sampling dates. Treatments with 0.40 kg a.i./ha of imazaquin, 2.0 and 4.0 kg a.i./ha of pendimethalin, and the hoe-weeded control, had the highest cowpea grain yield. The unweeded control had the lowest grain yield which was comparable to that in all other herbicide treatments. All treatments except 4.0 and 8.0 kg a.i./ha of pendimethalin had higher soybean grain yield than the unweeded control. Soybean yield was lowest in the unweeded control, and treatments that received 4.0 and 8.0 kg a.i./ha of pendimethalin. All rates of imazaquin gave similar soybean grain yields that were 29–41% higher than that from pendimethalin. The hoe-weeded control had the highest yield, which was 79% more than that in the unweeded control. Higher rates of imazaquin and pendimethalin reduced nodulation, nitrogen fixation, and vesicular arbuscular mycorrhizal (VAM) fungi colonisation in both crops. VAM fungi species diversity and species richness in cowpea rhizosphere soil and species diversity in soybean rhizosphere soil were reduced relative to the controls due to application of both herbicides with the rates of 0.10, 0.20, and 0.40 kg a.i./ha of imazaquin and 8.0 kg a.i./ha of pendimethalin being significantly effective.