Chemical Weed Management Research Articles

Herbicide Resistance Traits in Maize and Soybean: Current Status and Future Outlook.

This article reviews, focusing on maize and soybean, previous efforts to develop nontransgenic herbicide-resistant crops (HRCs), currently available transgenic HRC traits and technologies, as well as future chemical weed management options over the horizon. Since the mid twentieth century, herbicides rapidly replaced all other means of weed management. Overreliance on ‘herbicide-only’ weed control strategies hastened evolution of HR weed species. Glyphosate-resistant (GR) crop technology revolutionized weed management in agronomic crops, but GR weeds, led by Palmer amaranth, severely reduced returns from various cropping systems and affected the bottom line of growers across the world. An additional problem was the lack of commercialization of a new herbicide mode of action since the 1990s. Auxinic HRCs offer a short-term alternative for management of GR Palmer amaranth and other weed species. New HRCs stacked with multiple herbicide resistance traits and at least two new herbicide modes of action expected to be available in the mid-2020s provide new chemical options for weed management in row crops in the next decade.

Weed management practices in Argentina crops

AbstractData from surveys are used to help quantitatively diagnose the relative importance of chemical and nonchemical management practices, identify weed problems, and provide potential solutions. However, to our knowledge, such surveys have not been conducted in Argentina. In 2016, advisors and crop producers from cropping areas across Argentina were surveyed through email with the objectives to identify the main weed species problems and assess the use of chemical and nonchemical weed management practices in different crop production areas in Argentina. Fleabane, pigweed, johnsongrass, fingergrass, goosegrass, barnyardgrass, and ryegrass were considered the most important weeds. More than 53% of the producers used only chemical options; 86% used chemical fallow (i.e., keeping weed free with chemical application); 62% used full herbicide rates; 46% used proper herbicide timing; 41% used multiple modes of action; and 32% used rotation of herbicide modes of action. The main nonchemical practices used were crop rotation (45%); avoiding seed production during (31%) and after (25%) the crop cycle; narrow row spacing (19%); and cultivars with greater competitive ability (18%). Less than 15% of the people surveyed used increased crop densities or altered date of sowing. There is a high dependence on chemical control in the main crops grown in Argentina. Extension efforts are needed to emphasize the importance of integrated weed management.

Effectiveness of various chemical and non-chemical weed management practices as perceived by the farmers under cotton wheat cropping system in the Punjab

Effectiveness of various chemical and non-chemical weed management practices as perceived by the farmers under cotton wheat cropping system in the Punjab

Use of natural products for weed management in high-value crops: An Overview

Over the last five decades, weed management systems have relied primarily on synthetic herbicides. Due to the concerns over the potential impact of chemicals on human health and the environment, efforts are being made to reduce the heavy reliance on synthetic herbicides. To reduce synthetic herbicides, use of natural products such as essential oils, plant extracts, allelochemicals, agricultural by-products, and some microbes are gaining attention because they are safe due to their short environmental half-life and low toxicity. These natural product bioherbicides are a good alternative to synthetic herbicides especially in organic agriculture since they focus on environmental protection, practical viability, compatibility for integrated programs, and ecological stability. Most of the commercially available natural herbicides are non-selective and require careful application in order to preserve the crop of interest. Although many studies in this direction have been undertaken, the use of these natural products is still not common because of the difficulties in their synthesis due to their complex structure, cost effectiveness, poor results in field trials, and rapid degradation. No single above mentioned natural product has the potential to comprehensively replace chemical weed management; however, an integrated approach may provide better results. Thus, the role of bioherbicides in modern weed management is complementary rather than exclusive.

Candidate Tools for Integrated Weed Management in Soybean at the Northern Frontier of Production

AbstractThe development of early-maturing soybean [Glycine max(L.) Merr.] varieties has led to an increase in soybean production in canola (Brassica napusL.)-dominant crop rotations in western Canada. Herbicide-resistant (HR) volunteerB. napuscan be difficult to manage in HR soybean using herbicides alone. In 2013 and 2014, four field experiments were conducted in Manitoba, Canada, to evaluate soybean row spacing, seeding density, nitrogen supply, and interrow tillage as candidate nonchemical weed management tools for an integrated program to manage volunteerB. napusin soybean. Among treatments and sites, volunteerB. napusproduced about 830 seeds plant−1and resulted in large seedbank inputs (averaging about 20,300 seeds m−2). VolunteerB. napusseedling recruitment differed among sites, and resulted in two distinct classes of sites based on average seedling densities of 39 and 89 plants m−2. Weed management tools were more effective at the sites with higher volunteerB. napusdensities. At these sites, soybean yield was greater when using an increased soybean-seeding density (44% greater yield using a seeding density of 682,500 vs. 455,000 seeds ha−1) or interrow tillage (36% greater yield with vs. without using interrow tillage). Soybean row spacing (19 vs. 38 vs. 76 cm) did not affect soybean yield, unless the reduction in row spacing was combined with an increased seeding density (65% greater yield with narrow-row soybean seeded at 682,500 vs. wide-row soybean seeded at 455,000 seeds ha−1). At the sites with higher volunteerB. napusdensities, seed production of canola volunteerB. napuswas greater when nitrogen fertilizer was applied to simulate an environment with greater nitrogen supply (77% greater number of volunteerB. napusseeds produced with vs. without broadcast application of 23 kg N ha−1urea). In northern climates, seeding soybean at increased densities using narrow-row spacing in fields with limited soil inorganic nitrogen and using interrow tillage in wide-row production systems are effective strategies that could augment chemical weed management in an integrated program for management of volunteerB. napus, and perhaps also other competitive early-season weeds.

Herbicide based weed management in aromatic rice of Bangladesh

Selection of appropriate weed management strategy helps reduce rice yield loss due to weeds. Despite some undesirable side-effects, no viable alternative is currently available to shift the chemical weed management in rice. However, time of herbicide application is very important with respect to its efficacy. Keeping in mind the inevitability of herbicidal weed control, the current study was designed to evaluate the response of selected aromatic fine rice varieties of Bangladesh to different herbicides based weed management practices compare to farmers’ practices. The experiment was conducted in a randomized complete block design with three replications. The experiment consisted of five aromatic rice varieties; Kalijira, BRRI dhan34, BRRI dhan37, BRRI dhan38 and Binadhan-13, and six different weed management practices comprising no weeding, weed free, mechanical + manual weeding, pre–emergence herbicide + manual weeding, post–emergence herbicide + manual weeding and pre– + post–emergence herbicide. Eleven weed species belonging to five families were observed in the experimental plots. Based on the summed dominance ratio (SDR), grassy weed species Echinochloa crusgalli (SDR of 30.7) was the most dominant species, whereas broadleaf weed Nymphaea nouchali (SDR of 0.83) was the least one. Among the weed control treatments, application of pre–+ post emergence herbicides offered the highest reduction in weed density and biomass at all sampling dates which resulted in minimum crop-weed competition facilitating improvement in the yield contributing characters and finally resulted in the highest grain yield (2.5 t ha−1) and harvest index (30.7%) next to the weed free treatment. The variety BRRI dhan38 gave the highest grain yield (3.4 t ha−1) due to the highest performance of the yield contributing characters among the varieties. In interaction, BRRI dhan38 with pre–+ post–emergence herbicide application gave the highest yield (3.4 t ha−1) apart from the weed free treatment. Being efficient in weed density and biomass reduction as well as the highest yield producer, sequential application of pre–and post–emergence herbicides may be recommended for effective weed management practices in BRRI dhan38J. Bangladesh Agril. Univ. 16(1): 31-40, April 2018

A study on chemical weed management in boro rice: A review

Characteristically boro rice is winter season, photo-insensitive, transplanted rice cultivated on supplemental irrigation, often under conditions, where farmers’ are not able to take any other rabi season crop. Butachlor, pretilachlor, bispyribac-sodium and anilofos are the most commonly used herbicides for control of weeds in boro rice. Weed competition is one of the prime yield limiting biotic constraints resulting in yield reduction to the tune of 28 to 45%. Echinochloa spp., Cynodon dactylon, Portulaca quadrifida and Cyperus spp. are the major weeds responsible for yield reduction in boro rice. However, continuous and indiscriminate use of herbicides for a longer period may result in buildup of problematic weeds and also development of herbicide resistance in weeds. It is therefore, necessary to review the performance of promising herbicides for chemical weed management to improve the production and productivity of boro rice under the climate change scenario.

<b>Phytosociology of weed in the southwestern Goiás region

Roundup Ready® technology adoption and the cultivation of a second crop have changed chemical control methods and weed management in the southwest region of Goiás State, Brazil. Considering these changes, this study aimed to perform a phytosociological survey in areas with glyphosate resistant soybeans and conventional soybeans as the main harvest and sorghum, maize, millet or fallow in succession as the second harvest. A multivariate matrix of the floristic composition was constructed, and the indicator values of the individual number and dry biomass of species were measured. Based on the number of individuals, the species Chamaesyce hirta, Bidens subalternans, and Cissampelos ovolifolia were typical of areas cultivated with glyphosate-resistant soybean, while Euphorbia heterophyla presented indicator values of areas with conventional soybean cultivation. During the second harvest period, significant indicator values were observed for Crotalaria spectabilis in maize areas, Cenchrus echinatus in sorghum, and Commelina benghalensis, Sida glaziovii, Ipomoea grandifolia, Sida rhombifolia, and Ipomoea cordifolia in areas with millet. The species Conyza bonariensis was typical in the period before the herbicide application at post-emergence in harvest. Volunteer soybean presented as typical for the period before the herbicide application at post-emergence in the second harvest. Weeds that were difficult to control or were tolerant and resistant to the herbicide applications were recorded in the areas studied.

Abundancia y cobertura de arvenses bajo manejo convencional y orgánico de café y banano

Certain weeds can be used as cover species in bananas and coffee plantations. The objective of this study was to compare ground cover and abundance of weed species, between the organic and conventional production systems of banana and coffee. Selected farms under organic or conventional management located at Limón and Alajuela were surveyed for weeds, during 2015 and 2016. The minimum area methodology was used to determine sampling site size. At each sampling site, all weed species were identified and grouped into their respective taxonomic families. Percent soil cover by each species was also estimated by means of a visual scale. In both crops, weed diversity was higher when the herbicide glyphosate was used for weed control, although the ground cover for these species was kept at a minimum. These results are thought to arise from the fact that under the organic production system, a hierarchy of dominant species is established, which in turn inhibit many of the somewhat less adapted species, whereas under the conventional production system, the use of a non-residual herbicide renders the ground with plenty of space for species regeneration from the soil propagule bank. Organic weed management in both crops showed higher soil cover by weeds, but from a lower number of species. In contrast, chemical weed management with glyphosate showed a higher number at species, but a significant reduction in ground cover by those weeds.

PAM: Decision Support for Long-Term Palmer Amaranth (Amaranthus palmeri) Control

Palmer amaranth is the most troublesome weed problem in mid-southern US crop production. Herbicides continue to be the most commonly employed method for managing Palmer amaranth, despite the weed’s widespread resistance to them. Therefore, farmers need research and extension efforts that promote the adoption of integrated weed management (IWM) techniques. Producers, crop consultants, educators, and researchers would be more likely to deploy diversified chemical and nonchemical weed management options if they are more informed about long-term biological and economic implications via user-friendly decision-support software. Described within is a recently developed software that demonstrates the effects of Palmer amaranth management practices on soil seedbank, risk of resistance evolution, and economics over a 10-year planning horizon. Aiding this objective is a point-and-click interface that provides feedback on resistance risk, yield potential, profitability, soil seedbank dynamics, and error checking of management options.

Effect of chemical weed management on quality parameters, yield parameters and yield in sugarcane in western zones of Tamil Nadu

Effect of chemical weed management on quality parameters, yield parameters and yield in sugarcane in western zones of Tamil Nadu

High Planting Rates Improve Weed Suppression, Yield, and Profitability in Organically-Managed, No-till–Planted Soybean

High soybean populations have been shown to hasten canopy closure, which can improve both weed suppression and soybean yield. In conventional soybean production, the high cost of genetically engineered seed and seed treatments have led growers to plant at lower rates to maximize profitability. For organic farmers, market price premiums are typically double the price received for conventional soybean. Without chemical or mechanical weed management, cultural practices are particularly important for adequate weed suppression in cover crop–based organic no–till planted soybean production. In 2014, an experiment was conducted in Aurora and Hurley, New York, to assess the effects of increasing soybean planting rates on weed suppression, soybean yield, and partial economic return. Five planting rates ranging from 195,000 to 914,000 seedsha−1were arranged in a randomized complete block design. As soybean planting rate increased, weed biomass decreased and soybean yield increased at both sites. An asymptotic model described the relationship between increasing soybean planting rate and yield, and the estimated maximum yield was 2,504 kgha−1in Aurora and 3,178 kgha−1in Hurley. Despite high soybean populations, minimal lodging was observed. Partial returns decreased beyond the predicted economically optimal planting rate of 646,000 seeds ha−1in Aurora and 728,000 seeds ha−1in Hurley as higher seed costs were no longer offset by yield gains. Based on our results, planting rates that are more than double the recommended rate of 321,000 seeds ha−1for wide row (≥76 cm) conventional soybean management in New York can enhance weed suppression, increase yield, and improve profitability in organic no-till planted soybean production.

When herbicides don't really matter: Weed species composition of oil pumpkin (Cucurbita pepo L.) fields in Hungary

Oil pumpkin is a major emerging alternative crop with several unresolved weed management questions in central-eastern Europe, one of the focal regions of oil pumpkin production worldwide. This study aims to assess the importance of three groups of factors: environment, non-chemical management (all management excluding herbicides), and chemical weed management, in determining the weed species composition of oil pumpkin crops in Hungary. We surveyed the weed flora of 180 oil pumpkin fields across the country, along with 32 background variables. Applying a minimal adequate model consisting of 18 terms with significant net effects, 30.8% of the total variation in weed species data could be explained. Most variation in species composition was determined by environmental factors, with climatic conditions (precipitation and temperature) being most influential. The net effects of seven non-chemical management variables (preceding crop, N and P fertilisers, seeding rate, crop cover, cultivating tillage, and manual weed control), and two herbicides (S-metolachlor and linuron) were also significant. Variation partitioning demonstrated the dominance of environmental factors, and it also showed that non-chemical management practices accounted for five times more variance than herbicides. Within non-chemical management, the relative impact of cultural variables was nearly five times larger than that of mechanical weed management. Among the abundant weeds, Chenopodium polyspermum and Ambrosia artemisiifolia were positively associated with precipitation, Datura stramonium and Hibiscus trionum correlated with higher temperature, and Chenopodium album favoured larger potassium content of the soil. High seeding rate and crop cover suppressed Amaranthus retroflexus, cultivating tillage reduced Ambrosia artemisiifolia and Setaria pumila, while conspicuous tall weeds like Abutilon theophrasti and Chenopodium album were most vulnerable to manual weed control. Although the short stature of pumpkin with its poor weed-suppressive ability could unfavourably influence the results of some cultural practices, our findings suggest that the weed vegetation of oil pumpkin fields can be efficiently managed also with environmentally benign methods.

ALLELOPATHIC POTENTIAL OF QUINOA (CHENOPODIUM QUINOA WILLD.) GENOTYPES ON THE GERMINATION AND INITIAL DEVELOPMENT OF SOME WEEDS AND CROPS

Five quinoa (Chenopodium quinoa Willd.) genotypes; namely, KVL-SRA2, KVL-SRA3, Regalona, Q-37 and Q-52 were evaluated, under rainfed and irrigated conditions, for their allelopathic potential. Four concentrations of 1, 2, 4 and 8 g/100 ml of the aqueous extract of all plant parts were assessed for their effect on the germination and initial development of some weeds and crops. HPLC/DAD/MS analyses were conducted for genotypes with highly inhibitory effects to determine their contents of phenolic compounds and saponins. The estimated EC50 revealed that the aqueous extracts from genotypes grown under rainfed conditions had higher allelopathic activity than those genotypes grown under irrigated conditions. The suppressive effect of the extracts increased when the concentration of quinoa extracts increased. The highest reduction effects were achieved from Q-52; followed by Regalona and KVL-SRA2. Nevertheless, Q-37 and KVL-SRA3 caused minor amounts of inhibition in the tested plant traits. The negative influence of quinoa extracts was higher on monocotyledon plant species than on dicotyledon plant species. The highly susceptible plants were Hordeum vulgare, Allium cepa and Phalaris minor as compared to other tested plants. However, Vicia faba and Chenopodium album were slightly more susceptible plants. Qualitative-quantitative analysis showed sixteen flavonoids and three hydroxicinnamic acids (p-coumaroil derivatives); in particular, kaempferol dirhamnosyl-pentoside is the principal compound in Q-52 (11.25 mg/kg), while quercetin rhamnosyl-glucoside is the principal compound in Regalona (9.67 mg/kg). In quinoa, nine different aglycones, monodesmosidic, and bidesmosidic triterpene saponins were reported; in particular, in this work, hederagenin (hed), phytolaccagenic acid (PA), AG487, AG533 and AG515 derivatives were identified. Quinoa also contains biologically active phytoecdysteroids. Based on the bioassay results and its suppresive effect against weeds and crops, quinoa is considered as a crop with allelopathic potential that may have a negative impact on the growth of neighboring plants in the field and can be utilized for non chemical weed management.

Weed management in guava orchards

The comparative efficacy of orchard soil management practices like mulching (paddy straw, white polythene, black polythene) and weed control methods (mechanical and chemical) were evaluated for managing weeds growth in guava orchard. A weedy plot was also kept as control for comparative assessment of different orchard floor management practices. The results revealed a significant effect of different treatments on grassy as well as broad-leaf weeds in the orchard. Although the black polythene mulch kept the area weed free throughout the season, the paddy straw mulch exhibited promising results, with 69.1 and 93.2% reduction in total weed biomass during first and second year of application, respectively. The white polythene was poor performer as it resulted in heavy weed growth under the mulch and tearing of polythene sheet. Chemical weed management as well as mechanical weeding also reduced the intensity of weeds but resurgence of weeds resulted significantly higher weed biomass compared to paddy straw mulch. The paddy straw mulch exhibited potential to manage weeds in guava orchard.

Effect of different pre-and post-emergence herbicides on weed control, productivity and economics of maize

A field experiment was conducted at Agricultural Research Station, Vizianagaram, Andhra Pradesh during rainy seasons of 2015 and 2016 to find out the best chemical weed management practices in maize (Zea mays L.). Twelve treatments were tested in randomized block design with three replications. Treatments consisted of pre-emergence (PE) and post-emergence (PoE) herbicides applications along with weed free check and weedy check. Experimental results indicated that PoE of tank mix formulation of tembotrione 50 g/ha + atrazine 0.5 kg/ha at 15–20 days after seeding (DAS) has recorded highest weed control efficiency (93.6 and 96.9%, respectively during 2015 and 2016) followed by hand weeding twice at 20 and 40 DAS (90.1 and 95.6%, respectively). Grain yield was significantly higher (9.79 t/ha and 8.70 t/ha, respectively) with hand weeding twice at 20 and 40 DAS, and it was closely followed by PoE of tembotrione 50 g/ha + atrazine 0.5 kg/ha (9.65 t/ha and 8.61 t/ha respectively). Net monetary returns (` 104357 and ` 97985, respectively) and B: C ratio (2.94 and 3.14, respectively) were also significantly high with PoE application of tembotrione 50 g/ha + atrazine 0.5 kg/ha.

Agronomic Evaluation of Mechanical and Chemical Weed Management for Reducing Use of Herbicides in Single vs. Twin-Row Sugar Beet

Agronomic Evaluation of Mechanical and Chemical Weed Management for Reducing Use of Herbicides in Single vs. Twin-Row Sugar Beet

A “Stressed” Alfalfa-Based Cropping System Leads to the Selection of Quizalofop-Resistant Italian Ryegrass (Lolium perennessp.multiflorum)

Italian ryegrass populations investigated in this study were harvested in an alfalfa-based cropping system. In that system, the agronomic practices and chemical weed management, based on the use of aryloxyphenoxy-propionates herbicides (i.e., quizalofop ethyl ester), were optimized to obtain a dual seed–forage production. Five of seven populations tested were confirmed resistant to quizalofop ethyl ester with resistance indexes ranging from 4.5 to >209. Both target- and nontarget-site resistance mechanisms were most likely involved. Three allelic variants were detected (Ile-1781–Leu, Trp-2027–Cys, and Ile-2041–Asn) in four resistant populations, whereas no known mutations were found in one resistant population. The herbicide treatment on Italian ryegrass plants at different phenological stages suggested that to control regrowth, it is necessary to use two to fives times the herbicide dose suitable for younger plants. This situation is encountered in fields when Italian ryegrass plants need to be controlled to maximize the alfalfa seed production, and it is comparable to using a sublethal herbicide dose, leading to the selection of herbicide-resistant biotypes. In such a situation, the cropping system is not sustainable, and integrated weed management should be implemented to deplete the soil weed seed bank and prevent new weed seed production.

Meta-Analysis of Crop and Weed Growth Responses to Arbuscular Mycorrhizal Fungi: Implications for Integrated Weed Management

Integrated weed management (IWM) relies upon multiple chemical, physical, or biological weed management techniques to achieve an acceptable level of weed control. Agents that selectively suppress weeds but not crops and that can be manipulated in agriculture will be promising components for inclusion in IWM. We used a meta-analytic approach to investigate the potential of arbuscular mycorrhizal fungi (AMF) to contribute to IWM. We quantified the effect of crop and weed host status (strong and weak AMF hosts are divided in this study by a 10% root length colonization threshold), AMF diversity (single vs. mixed), and soil N and P fertility management on plant mycorrhizal growth responses (MGRs). Our results indicated that weak host weeds had consistently lower MGRs than strong host crops in both controlled and field conditions. Moreover, these differences in MGRs between weak host weeds and strong host crops were more pronounced under mixed AMF inoculum and low N and P nutrient availability. In contrast, MGR of strong host weeds was not different from strong host crops in general. However, we observed a wide range of MGRs among strong host weeds, some of which had much lower MGRs than strong host crops. In addition, in the presence of N and P fertilizers, strong host crops had a stronger positive response to AMF than strong host weeds. Thus, our meta-analysis indicates that AMF have potential to contribute to weed control by direct and indirect pathways: directly suppress weak host weeds, and indirectly suppress some strong host weeds mediating by competitive effects exerted by strong host crops. We suggest that management practices affecting AMF diversity and crop and weed mycorrhizal responses could be chosen to improve the contribution of AMF to IWM. Better understanding is needed of crop–weed–AMF interactions and management practices that enhance this form of weed management.

Chemical weed management in Brassica rapa var. yellow sarson

Field experiments were conducted for three years at Pulses and Oilseeds Research Station, Berhampore, Murshidabad, West Bengal, India during rabi 2008, 2009 and 2010 to develop an efficient chemical weed management practice with newer herbicidal molecules in yellow sarson. The experiment was laid out in a randomized block design with three replications having eleven treatments. Experimental results revealed that highest seed yield (1456 kg ha-1) was recorded under the treatment twice hand weeding and lowest with weedy check (910 kg ha-1). Twice hand weeding recorded 60% higher seed yield over weedy check. Application of chemical herbicides significantly improved the seed yield over W0 at 5% level of significance.. Among the chemical weed control measures, application of Pendimathalin @ 1 kg a.i./ha (PE) recorded highest seed yield (1320 kg ha-1) of yellow sarson, which was found at par with application of Pendimathalin @ 1.5 kg a.i./ha (PE), Fluchloralin @ 1.5 kg a.i/ha (PPI) and Clodinafop @ 0.06 kg a.i./ha ( 25-30 DAS). Chemical weed management practices increased the seed yield of yellow sarson by 25.3 to 45.1% over weedy check. Highest weed control efficiency (86.4%) was recorded with hand weeding twice. Significant reduction in the total weed density and total weed dry weight were found with the application of chemical herbicides at 5% level of significance. Among the chemical herbicides Pendimathalin @ 1 kg a.i./ha (PE) recorded highest weed control efficiency (81.7%). Chemical weed control measures increased the total microbial population by 26.5 to 89.4% over weedy check and 6.6 to 59.6% over twice hand weeding and thus proved to be environmentally safe and economic for managing weeds in yellow sarson.