Journal of Research in Weed Science
Volume:3 Issue: 3, Sep 2020

Smallholder farmers have challenges of weed control and mostly they use cultural control methods because chemical control with herbicides is usually costly. However, Lantana camara L. is known to be allelopathic to other plants hence a worthy candidate for biological control of weeds under cowpea production. A field study was conducted to determine the potential for L. camara to control weeds in cowpea at the University of Zambia Agricultural Experimentation Station. Leaves were harvested from two genotypes of L. camara (G1: Pink-flowered and G2: Orange-flowered genotypes) dried and pulverized to form a powder and applied at different rates (R0C: 0 kg ha-1, R1: 100 kg ha-1, R2: 200 kg ha-1, R3: 400 kg ha-1) using the following types of application: T0C: No application, T1: broadcasting, T2: incorporation in the soil and T3: spraying of soaked ground L. camara. The research was conducted at the University Of Zambia School Of Agricultural Sciences Field Station. The experiment was arranged in a split split-plot design with three replications. Weed population density and weed weight were reduced the most (38% and 12.5%, respectively) at the highest rate (R3: 400 kg ha-1) of L. camara application. The cowpea grain yield was higher (P< 0.05) in fields treated with G1 (mean =876.90 kg ha-1) than for G2 (mean =672.10 kg ha-1). G1 increased cowpea grain yield by 36.04%. Lantana camara holds great potential to increase food security by reducing losses associated with weeds in cowpea.

This study was performed to evaluate the weed density and weed control efficiency (WCE) on transplanted rice under different treatments at a farmer’s field, Bhanu-11, Rupakot, Nepal during Rainy season of 2017. Ten treatments (one manual weeding at 21 days after transplanting (DAT) (T1); two manual weeding at 21 and 42 DAT (T2); three manual weeding at 21, 42, and 63 DAT (T3); single cono weeding at 21 DAT (T4); double cono weeding at 21 &42 DAT (T5); triple cono weeding at 21, 42, and 63 DAT (T6); butachlor as pre emergence (T7); butachlor with single manual weeding at 21 DAT (T8); butachlor with double manual weeding at 21 & 42 DAT (T9) and weedy check (T10) were laid in randomized complete block designs (RCBD) with three replications. At 30 DAT, the highest weed density was recorded at unweeded check (T10) while it was the lowest at butachlor with double manual weeding (T9). At 60 DAT the effective weed control method on weed density was found to be double manual weeding (T2). At 90 DAT triple cono weeding (T6) was found to be more effective on controlling weed density (30) and was at par double manual weeding (T2), double cono weeding (T5) and butachlor with double manual weeding (T9). WCE was the highest in the plot treated with butachlor with double manual weeding at 21 and 42 DAT (T9) and the lowest in the plot treated with butachlor pre emergence (T7) at 30 DAT. At 90 DAT, WCE in the plot treated with triple weeding (T6) was found the highest (78.63%) and the lowest in the plot treated with butachlor as pre emergence (T7) (26.14%).

Herbicide efficacy could be enhanced by herbicide combinations and addition of surfactants. These substances improve absorption of herbicides by lowering the surface tension of spray droplets resulting in increased area of contact of the herbicide solution with the leaf surface. This experiment determined the tolerance of rice and efficacy of three post-emergence herbicides in varying combinations with surfactants against Echinochloa crus-galli (L.) Beauv., Cyperus iria L., and Ludwigia octovalvis (Jacq) Raven. The study was conducted at the Cambodian Agricultural Research and Development Institute (CARDI), in Cambodia from January to February 2019. Rice at 10 days after herbicide application (DAHA) showed some degree of susceptibility to Pyribenzoxim- and Quinclorac 50%+ Pyrazosulfuron-ethyl 7% + Fenoxaprop-P-ethyl 13% pre-mix-surfactant mixture but was fully recovered at 20 DAHA. Generally, rice was more tolerant at the 4-6 than at the 2-3 leaf stage. Phytotoxicity of the herbicides to Echinochloa crus-galli depended on the herbicide and surfactant concentration and the stage of growth of the weed at application time. Cyperus iria and Ludwigia octovalvis were relatively more sensitive to the pre-mix alone and where, in most instances, did not merit addition of surfactant.

A two-year (2017 and 2018) field trials was conducted in the School of Agriculture, Njala University, Sierra Leone, to evaluate weed management practices on weed dynamics and productivity of maize. The experimental trials were laid out in a randomized complete block design (RCBD) with three replications. The treatment combinations comprised of weedy check (Control), two hoe weeding at 4 and 8 weeks after planting (WAP), Double force® at 4 L ha-1 plus one hoe weeding at 8 WAP, Gliricidia sepium leaves mulch at 40 kg m-2 plus one hoe weeding at 8 WAP, weed-free check and Atrazine 500 SC at 3 L ha-1 plus one hoe weeding at 8 WAP. The results showed that growth and yield physiognomies differ significantly (P<0.05) among weed control practices across both years. The weed-free check treatment recorded the highest growth and yield physiognomies with respect to reduced weed density and increased weed control efficiency followed by herbicidal treatments, while weedy check had the lowest growth and yield attributes across both years. Nonetheless weed-free check required lot of labour force which was not economical to the farmer’s point of judgment. Thus, Double force® at 4 L ha-1 plus one hoe weeding at 8 WAP proved to be better in controlling weeds, increasing crop yield and economical compared with other weed management practices. Hence Double force® at 4 L ha-1 plus one hoe weeding at 8 WAP was recommended as a pre-emergence herbicide in maize production for effective and environmentally friendly weed control method.

Application of crop residues can be a good option for organic and sustainable weed management in rice. Consequently, the use of crop residues can suppress weed emergence and weed biomass. A study was conducted in two consecutive seasons firstly to optimize the mixture ratio to soil (v/v) of different crop residues on inhibition of common weed species and secondly to evaluate their performance on rice growth and yield. Among the crop residues used in this study sorghum was the most effective followed by mustard, barley, soybean, rice, wheat, triticale, maize, lentil and grasspea. The 50:50 (crop: soil, v/v) treatments incorporation rate of all crop residues suppressed the growth of all weed species in maximum level. The result revealed that broadleaf weed species were more susceptible to crop residues than grass weed species. In this respect, the highest growth inhibition (54.49%) was observed in controlling Monochoria vaginalis. Variety and rate of sorghum residues application significantly influenced weed growth and inhibition. A maximum increment in terms of plant height, dry weight and yield was observed due to sorghum 2.0 t ha-1 residue applications. Considering yield and yield contributing characters, highest grain and straw yield was obtained from BRRI dhan29. All together, the result depicted that crop residues can effectively control weed along with enhancing growth and yield of rice and it can be successfully used in weed management program in rice.

Growing two or more cultivars of same crop species in mixture reduces intra-specific competition for natural resources and increases competitive ability of crops against weed growth and thus enhances crop yield. The objective of this study was to evaluate the potentiality of growing rice cultivars in mixtures in temporal dimension for minimizing weed pressure and increasing rice yield and to determine the best time of introduction of one cultivar in relation to another cultivar. The experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh during aman season (July-December) 2017. Two transplanted aman rice cultivars having different plant height and growth duration viz. Binadhan-13 (tall, late- maturing and fine grained aromatic rice cultivar) and BRRI dhan49 (semi-dwarf, mid-maturing and coarse grained rice cultivar) were used in this study. The experiment comprised time of introduction of BRRI dhan49 namely 7 days before Binadhan-13, 7 days after Binadhan-13, same day as Binadhan-13, Binadhan-13 as sole crop, BRRI dhan49 as sole crop and three different weeding regime namely weedy, recommended weeding and weed free. The experiment was laid out in a randomized complete block design (RCBD) with three replications. Both the cultivars showed better growth and higher yield when grown in mixture rather than sole culture. Transplanting of one cultivar before or after another cultivar produced more yield and suppressed weed better than transplanting of two cultivars on the same day. Thus only spatial arrangement produced no advantages over sole culture. Among the weeding regimes, weedy treatment performed the worst, while recommended weeding and weed free treatment performed similarly. Therefore, for better weed suppression and higher production, BRRI dhan49 may be transplanted 7 days before or after Binadhan-13 in 1:1 ratio following recommended weeding.

Two experiments were carried out to study the efficacy of herbicides with different rates for controlling broadleaf and narrow leaves weeds, growth and yield parameters of onion. The treatments of herbicides applied include the single of active ingredient and their combinations. The single of active ingredient such as Oxyfluorfen at the dose of 270; 180; and 90 g a.i./fed, Clethodim at the dose of 93.75; 62.5; and 31.25 g a.i./fed. The combination used the Oxyfluorfen + Clethodim such as 270+93.75; 180+62.5; and 90+31.25 g a.i./fed. Results showed that Weed control efficiency (WCE) for broadleaves species the maximum percent was recorded for Oxyfluorfen (270 g a.i./fed). In controlling narrow leaves weed species, the maximum percent was recorded in Clethodim (93.75 g a.i./fed). While controlling broadleaf and narrow leaves weeds, the maximum percent was recorded in Oxyfluorfen + Clethodim (270+93.75 g a.i./fed). Growth, and yield parameters as plant height, bulb weight and bulb diameters were recorded maximum in Oxyfluorfen + Clethodim (270+93.75 g a.i./fed) compared to rest for the treatments. We suggest that the best treatment was Oxyfluorfen + Clethodim (270+93.75 g a.i./fed) for controlling all species of weeds in the onion plant.

Seed germination of some crops (Brassica campestris and Triticum aestivum) and weed seeds (Ageratum conyzoides, Bidens pilosa, Cyperus rotundus and Galinsoga parviflora) was studied under different environmental conditions like moisture (concentrations 3, 6, 9, 12, 15ml), temperature (5, 10, 15, 20 and 25˚C), pH (value 4, 5, 6, 7, 8 and 9) and light (normal, red, yellow, blue, green and dark color). For the crops too much lower or higher moisture was not favorable for germination and growth. Experiments under different moisture conditions showed that C. rotundus and G. parviflora do not require more moisture to germinate and grow. Seed germination of both crops enhanced insignificantly at 15 to 20˚C treatments. Seed germination of all weed seeds was insignificantly high at 10 to 15˚C. The percentage of seed germination of both crops increased significantly in normal and green light. Seed germination of A. conyzoides, C. rotundus and G. parviflora was insignificantly different in normal, red, yellow and green light. Germination of all weed seeds was completely inhibited by blue and dark light. The shoot and root length of weed A. conyzoides was found to be significantly high (P=0.05) in yellow light treatment, but in B. pilosa, it was high in red and green light. Similarly in C. rotundus, shoot and root length were high in normal light but in of G. parviflora it was high in green light treatment. Seed germination and seedling growth were higher in pH5-7 in most cases.

The use of weeds as insectary plants is an emerging management tactic by agroecologists to sustain beneficial insect species. Fallow lands have always been used by insects, and are an important part of their diet in fragmented ecosystems. Weeds provide nectar and floral resources to beneficial insects, and provide resources to keep those insects within a field in between flowering events. Using weeds as a tool in agricultural production reliant on pollination allows farmers to increase yield, end herbicide use, and increase biodiversity of both plants and insects. Native weeds expand the range of native insects from natural areas into agroecosystems, supporting insects that buffer against lapses in pollination by agricultural honey bees. Weeds also support parasitoid and predatory insects by providing nectar and pollen to adults, as well as alternative prey. This review examines the plant-insect ecological interactions supported by weeds left within a farm, and their potential role in supporting pollinators and parasitoids.

Oilseed rape (OSR) has one of the highest potential for gene flow through seed and pollen. Volunteer plants are one of the most important sources of contamination of OSR crop of different quality cultivars. The aim of this study was to estimate the abundance of soil seed bank after the harvest of high erucic (HE) cultivar Maplus and to determine biochemical and molecular characteristics of OSR volunteers. The investigation comprised volunteers of oilseed rape obtained from the soil seed bank in two localities in Poland: Dlon and Zielecin (Greater Poland Voivodeship). The seeds of volunteers and reference cultivars were analyzed using biochemical (erucic acid and glucosinolates [GLS]) and molecular biology methods. In seeds of volunteers, erucic acid content ranged from 0 to 57.4% of all fatty acids and glucosinolate content ranged from 5.2 to 105.0 µmol g−1 of seeds. In sowing seeds of the cultivar Maplus, the erucic acid content was 57% and total glucosinolates were 12.6 µmol g−1 of seeds. RAPD markers were used to determine genetic similarity coefficient and relationship between polymorphic RAPD markers and erucic acid and total GLS content. Twenty RAPD markers showed statistically significant association with erucic acid and GLS content in seeds. Volunteers originating from the investigated soil seed bank were characterized by different content of erucic acid and GLS in seeds typical for different types of oilseed rape cultivars: double low (00, canola type), cultivars with zero erucic acid and high GLS content (0HG) and traditional cultivars with high erucic acid and high GLS content (HEHG). The results of this study, especially the presence in soil seed bank the seeds of very old cultivars, confirm that seeds of rapeseed of different origin may persist for a long time at the stage of secondary dormancy.