Lowest Weed Density Research Articles

Weed flora and seed yield in quinoa crop (Chenopodium quinoa Willd.) as affected by tillage systems and fertilization practices

The effects of tillage system and fertilization regimes on weed flora in quinoa (Chenopodium quinoa Willd.) were evaluated by means of two field experiments in 2011 and 2012. The experiments were laid out in a split-plot design with two main plots (conventional and minimum tillage) and four sub-plots (fertilization regimes). The results indicated that weed biomass and density in quinoa were influenced by the different fertilization and tillage treatments. Moreover, seed yield in conventional was 5%–13% higher than that of minimum tillage, probably due to the lower weed density and biomass. Concerning fertilization treatments, total weed density and biomass increased under manure application and inorganic fertilization. Tillage effects on weeds were species specific. The density of perennial weeds such as purple nutsedge (Cyperus rotundus L.) and the density of small-seeded weeds such as redroot pigweed (Amaranthus retroflexus L.) and common purslane (Portulaca oleracea L.) were significantly lower under the conventional tillage than under the minimum tillage system.

Common bean canopy characteristics and N assimilation as affected by weed pressure and nitrogen rate

SUMMARYCrop canopy characteristics and management factors that affect the canopy structure can influence crop competitive ability against weeds. The goal of the current study was to understand the interaction between nitrogen (N) fertilizer rate and redroot pigweed (Amaranthus retroflexus) density on common bean (Phaseolus vulgarisL.) canopy characteristics and N assimilation. Experiments were conducted to determine the growth responses of two bean genotypes with contrasting growth habits to different N fertilizer rates under no, low and high redroot pigweed pressure. Nitrogen was applied at rates of 0, 50, 100 and 200 kg/ha for a semi-erect variety and 0, 35, 70 and 140 kg/ha for an erect bean variety. Leaf area index (LAI), leaf area duration (LAD), leaf chlorophyll, N assimilation and N assimilation rate for both bean growth habits increased with N application rate at no and low weed density. The negative effect of redroot pigweed competition on LAI, LAD, N assimilation and N assimilation rate increased with redroot pigweed density, and with N application rate for the high weed density. Stepwise multiple regression analysis showed that N assimilation and chlorophyll concentration accounted for 0·73–0·87, overall, of the variation in yield loss due to weed competition. It is concluded that greater N assimilation in the semi-erect growth habit compared with the erect growth habit is the cause of its higher competitive ability against the weed, as it improves the effective canopy traits that confer potential for resource pre-emption.

Performance of sequential herbicides in dry-seeded rice in the Philippines

Economical and sustainable weed management in dry-seeded rice (DSR) depends on appropriate combinations of potential pre-emergence and post-emergence herbicides. A field study was conducted during the dry seasons of 2013 and 2014 at the International Rice Research Institute, Philippines, to evaluate the weed control efficiency of some pre- and post-emergence herbicide combinations in a DSR system. The herbicide treatments were: (i) oxadiazon 750 g ai ha � 1 was sprayed at 1 DAS fb 2,4-D 500 g ai ha � 1 at 28 DAS; (ii) oxadiazon 750 g ai ha � 1 was sprayed at 1 DAS fb bispyribac-sodium 30 g ai ha � 1 at 14 DAS fb 2,4-D 500 g ai ha � 1 at 28 DAS; (iii) oxadiazon 750 g ai ha � 1 was sprayed at 1 DAS fb bispyribac-sodium 45 g ai ha � 1 at 14 DAS fb 2,4-D 500 g ai ha � 1 at 28 DAS; (iv) bispyribacsodium 30 g ai ha � 1 was sprayed at 14 DAS fb 2,4-D 500 g ai ha � 1 at 28 DAS; and (v) bispyribacsodium 45 g ai ha � 1 was sprayed at 14 DAS fb 2,4-D 500 g ai ha � 1 at 28 DAS. The lowest weed density (22e28 plants m � 2 ) and biomass (7e16 g m � 2 ) were found in the plots treated with oxadiazon fb bispyribac-sodium 45 g ha � 1 fb 2,4-D. However, weed density and biomass in this treatment were similar to that in the treatment oxadiazon fb bispyribac-sodium 30 g ha � 1 fb 2,4-D. The highest weed density (123e239 plants m � 2 ) and biomass (108e149 g m � 2 ) were recorded in the plots treated with bispyribacsodium 30 g ha � 1 fb 2,4-D. The plots treated with oxadiazon fb bispyribac-sodium 30 g ha � 1 fb 2,4-D had 12e14% higher rice grain yield than the plots that did not receive bispyribac-sodium (i.e., oxadiazon fb 2,4-D), and 20e25% higher grain yield than the plots that did not receive oxadiazon (i.e., bispyribacsodium 45 g ha � 1 fb 2,4-D). The results suggest that pre-emergence herbicides must be used in DSR

<b>Interference of weeds on seedlings of four neotropical tree species

Seasonal semideciduous forests in southeastern Brazil have experienced intensive fragmentation, and the interference of weeds may affect the dynamics of restored communities. The purpose of this study was to determine if there were specific densities of the weeds Urochloa decumbens and Ipomoea grandifolia at which the growth of seedlings of four Neotropical tree species – Senegalia polyphylla and Enterolobium contortisiliquum (Fabaceae) and Ceiba speciosa and Luehea divaricata (Malvaceae) – would be negatively affected. A randomized experimental design was conducted in a greenhouse, with five treatments to each tree species (different weed densities per pot per tree species) and four replicates per treatment. After the weeds flowered, the height and stem diameter of seedlings were quantified, including the aboveground dry biomass and the percentages of macro and micronutrients contents in the leaves. The growth of the tree seedlings was affected by the lowest weed density (two weeds per pot) when interacting with U. decumbens or I. grandifolia. In general, significant decreases in the percentage of macro and micronutrients in the leaves were observed, especially at eight weeds/pot. Such results could warrant experimental practices in chemical control in conjunction with alternative methods to control of these two weeds in restored areas.

Effects of weed density on the dispersal of Orius majusculus Reuter (Heteroptera Anthocoridae) within maize

AbstractOrius majusculus Reuter (Heteroptera: Anthocoridae) is the most common and abundant generalist predator in Spanish maize crops and is sensitive to drastic changes in weed density. We carried out a 2‐year study in the NE Iberian Peninsula to examine the dispersal of O. majusculus in maize plots with moderately high and low weed density. Insects were collected using yellow sticky traps and/or a bug‐vac aspirator. Dispersal was assessed using rubidium as a marker. Dispersal rate of O. majusculus differed between sampling periods, with a maximum between the 16 unfolded leaves (V16) to grain milky (R3) maize growth stages. However, we detected no differences in the distance moved by male and females of O. majusculus from rubidium‐marked areas in plots with moderately high or low weed density suggesting that changes in weed density do not affect the dispersal of O. majusculus within a maize field.

Integrated weed management approach to improve weed control efficiencies for sustainable rice production in dry-seeded systems

Weed management is the major challenge to the success of dry-seeded rice (DSR). A field study was conducted during the dry seasons of 2013 and 2014at the International Rice Research Institute to evaluate the performance of herbicides combined with mechanical weeding in DSR. The lowest weed density and biomass were found in the treatment oxadiazon followed by (fb) fenoxaprop+ethoxysulfuron fb 2,4-D fb mechanical weeding (MW) at 42 days after sowing (DAS). However, this treatment had similar weed density and biomass to the treatments oxadiazon fb bispyribac-sodium fb fenoxaprop+ethoxysulfuron fb 2,4-D,oxadiazon fb bispyribac-sodium fb 2,4-D, and oxadiazon fb MW (28 DAS) fb MW (42 DAS). The highest weed density and biomass were recorded in the treatment oxadiazon fb MW (28 DAS) and oxadiazon fb 2,4-D. Higher grain yield (5.3-5.8tha-1) was produced in the plots that received oxadiazon fb fenoxaprop+ethoxysulfuron fb 2,4-D fb MW(42 DAS) and oxadiazon fb bispyribac-sodium fb fenoxaprop+ethoxysulfuron fb 2,4-D. The results of this study provide sustainable weed management options to farmers growing DSR.

English

Field experiments were conducted during 2013-2014 crop seasons at Ambo and Guder to study the effect of weed control methods on weed dynamics in maize (Zea mays L.) variety BH-660 in randomized complete block design with three replications. Five treatments, including Nicosulfuron (Arrow 75 WDG) at 0.09 kg ha-1 + silwet gold (adjuvant) at 0.10%, s-metolachlor 290 + Atrazine (Primagram) at 3.00 kg ha-1, s-metolachlor (dual gold) 1.5 kg ha-1, and hand weeding and weedy check (control) were used. Effect of different herbicides on weed density was significant. The lowest weed density (0.71 and 4.99 m-2) was recorded in plot treated with hand weeding followed by Nicosulfuron at 0.09 kg ha-1 (3.68 and 5.92 m-2) whereas the maximum was recorded in weedy check (14.16 and 24.24 m-2) in Guder and Ambo, respectively. Like density and dry weight of weeds, the minimum was observed in hand weeding and hoeing followed by Nicosulfuron at 0.09 kg ha-1 which is not significantly different from s-metolachlor at 1.50 kg ha-1 and the lowest dry weight of weeds (0.0 and 26.67 gm-2) was recorded in plot treated with hand weeding  followed by Nicosulfuron at 0.90 kg ha-1 (2.13 and 65.60 gm-2), however, non-significant difference existed among them in Guder, whereas the highest was observed in weedy check (170.93, 382.13 gm-2) in Guder and Ambo, respectively. Moreover, those treatments also significantly increased the yield and yield component of maize in both locations.   Key words:  Weed, weed control methods, herbicides, maize yield. 

Evaluation of New Herbicide (Bispyribac sodium 10 SC) on Weed Control and Yield in Direct Seeded Lowland Rice (Oryza sativa)

Field investigation was carried out to evaluate the new formulation of bispyribac sodium 10 SC in direct seeded rice during rabi (August to February) of 2011-12 at Tamil Nadu Agricultural University, Coimbatore. The experiment was laid out in a randomized block design and replicated thrice with the objective to find out the effect of bispyribac sodium 10% SC on weed control efficiency and yield of direct seeded rice. The treatments consist of EPOE application of bispyribac sodium 10% SC at 10, 20, 40 g ha -1 , nominee gold 20 g ha -1 (bispyribac sodium 10 SC) on 15 DAS and PE butachlor 1.5 kg ha -1 , anilophos 0.45 kg ha -1 , pretilachlor S 0.45 kg ha-1 on 3 DAS + HW on 40 DAS and power weeder, conoweeder weeding at 20 and 40 DAS, HW twice on 20 and 40 DAS and unweeded control. Application of pretilachlor S 0.45 kg ha -1 on 3 DAS + HW on 40 DAS registered lower weed density and dry weight at 20 DAS but during the later stages of crop growth EPOE application of bispyribac sodium 10% SC 40 g ha -1 recorded lower weed density and dry weight. The grain and straw yield in both the treatments were comparatively higher than other treatments.

Herbicidal Combinat ion for Effect ive Management of Complex Weed Flora in Transplanted Rice (Oryza sat ivaL.)

Long term continuous use of similar herbicide is major culprit for weed shift and herbicide resistance. Therefore, a field experiment was conducted at Norman E. Borlaug Crop Research Centre of G.B. Pant University of Agriculture and Technology, Pantnagar during kharif 2012 to evaluate the performance of new broad spectrum herbicide molecules. Pre-emergence application of Pretilachlor 750 g ha−1 with no irrigation during initial one week along with post-emergence application of Bispyribac-Na 20 g ha−1 provided broad spectrum control of complex weed flora at 30 and 60 days after transplanting (DAT) resulted in significantly lower weed density and dry matter than rest of the weed control treatments. This treatment thus, provided higher weed control efficiency (98.7%) and yield (5729 kg ha−1), than test treatment i.e. pre-emergence application of Pretilachlor alone. However, one conoweeding (15 DAT)+one hand weeding (45 DAT) recorded higher weed density and dry matter at both the stages. Alone post-emergence application of Bispyribac-Na and twice hand weedings produced at par yield with Pretilachlor 750 g ha−1 with no irrigation during initial one week along with application of Bispyribac-Na 20 g ha−1. Among different doses of Penoxsulam, the increase in dose of Penoxsulam caused significant reduction in weed density and dry matter thus registered higher grain yield. Post-emergence application of Penoxsulam at 22.5 and 25 g ha−1 produced comparable yield with Bispyribac-Na. Conoweeding + one hand weeding was found least effective compared to rest of the treatments.

Effect of Herbicide Application on Weed Management in Green Gram [Vigna radiata (L.) Wilczek

A field experiment was carried out at Bidhan Chandra Krishi Viswavidylaya (Nadia, West Bengal) during 2012 and 2013 (during March-May) in upland situation to judge the efficacy of the herbicides against weed flora in green gram crop field and also to find out the effect of herbicides on growth, yield and benefit cost ratio of green gram [Vigna radiata (L.) Wilczek] crop. The soil of experimental site was sandy loam in texture having neutral in soil reaction.The experiment was conducted with 14 treatments and laid out in Randomized Block Design with 3 replications. The green gram variety used was IPM-2-3. It was observed that hand weeding resulted in significantly lower weed density and dry weight and gave better seed yield of green gram. Most of the herbicides were found effective in controlling weeds and maximizing seed yield of green gram. These treatments were at par with hand weeding twice at 20 and 40 DAS. Total weed free treatment showed the best performance in respect of yield and yield attributes of green gram crop and weeds management. The herbicidal treatments Fenoxaprop-p-ethyl@50 g a.i. ha-1 and @ 100 g a.i. ha-1 were found less effective for controlling weeds. Maximum benefit: cost ratio was obtained from Vellore 32(Pendimethalin 30 EC+Imazethapyr 2 EC)@1.00 kg a.i. ha-1. Hand weeding treatments, though significantly reduced weed biomass and improved the grain yield, gave less benefit: cost ratio owing to higher cost of farm labour.

Weed community composition after 43 years of long-term fertilization in tropical rice–rice system

Abstract Biodiversity is central to the study of biology and research on the effects of human activities on biodiversity is becoming increasingly important as extinction levels increase. Many factors are increasing extinction levels, and continuous nitrogen application may be one of the reason driving terrestrial extinctions. Understanding the response of arable weed community assembly to fertilization is important for designing better weed management strategies in tropical rice–rice systems and also for changes in weed biodiversity. The cumulative effects of various fertilization treatments on weed species composition and diversity along with rice growth and yield were investigated in a long-term fertilizer experiment established 43 years ago in CRRI, Cuttack, India. A total of 20 weed species were observed in the study, out of which 6 species (i.e., Cyperus difformis, Cyperus tenuspica, Fimbristylis miliacea, Echinochloa colona, Oldenlandia corymbosa, Lindernia anagallis) occurred in all treatments and remaining species occurred only in some of the treatments. Sedges were dominant in all the treatments followed by broad-leaves and grasses, high relative density of weeds was observed in control and FYM treated plots, whereas, low weed density was observed in N, NPK and NPK + FYM treatments. The indices of species diversity (species richness, Shannon–Wiener, Pielou and Simpson indices) showed linear relationships with rice yield. The balanced fertilization was more efficient at inhibiting the potential growth of weeds because of the increased growth of rice leading to competition for nutrients. Principal component analysis showed that changes in the weed community composition were due to application of P and FYM. Balance fertilization showed a positive effect on rice yield and negatively affect weeds density, although the effect is negative but balance fertilization is not resulted in species elimination or hampered biodiversity.

Integrated management of Bromus diandrus in dryland cereal fields under no‐till

SummaryAs herbicides have limited effect in controlling Bromus diandrus in no‐till dryland cereal fields, the integration of chemical and cultural methods needs to be investigated. A field study was carried out in Lleida (Spain) during 2008–09, 2009–10 and 2010–11 seasons, in a no‐till winter cereal field integrating delayed crop sowing with herbicides in a barley–wheat–wheat rotation. Three crop sowing dates were considered: D1, mid‐October; D2, mid‐November; and D3, early December, and the herbicides mesosulfuron‐methyl plus iodosulfuron‐methyl‐sodium were applied in wheat. Weed density, cumulative emergence and fecundity were estimated for each sowing date. In all three seasons, a significant reduction in the cumulative emergence of B. diandrus as compared to D1 was observed in D2 (82.0, 97.5 and 98.1%) and D3 (80.8, 98.7 and 97.2%). In addition, a significant decrease in weed density and seed rain was observed across all sowing dates and seasons. The herbicide used in wheat was more effective under delayed sowing, due to lower weed density and presence of less developed weed seedlings. After three seasons, the populations of B. diandrus were completely depleted in D2 and D3. This study demonstrates the possibility of eliminating brome infestations in dryland cereal fields in no‐till systems through the integration of cultural and chemical strategies.

Comparison of two populations of Pseudophilothrips ichini (Thysanoptera: Phlaeothripidae) as candidates for biological control of the invasive weed Schinus terebinthifolia (Sapindales: Anacardiaceae)

Brazilian peppertree, Schinus terebinthifolia Raddi (Sapindales: Anacardiaceae) (hereafter Schinus), is one of the worst invasive species in Florida and Hawaii. The thrips Pseudophilothrips ichini Hood (Thysanoptera: Phlaeothripidae) is being considered as a potential biological control agent of Schinus. Two populations of this thrips were collected in the weed's native range; one from central-east Brazil (Ouro Preto thrips) and a second from north-east Brazil (Salvador thrips). Temperature requirements, adult fecundity and impact on different plant haplotypes by P. ichini were examined in the laboratory. Complete development of thrips from both populations occurred at temperatures ranging from 20 to 30°C. Two approaches were used to model the predicted distributions of the thrips populations in the USA: the physiological model (NAPPFAST) based on cold tolerance and the ecological niche model based on climatic variables (MaxEnt). The physiological model predicted that both populations of P. ichini may establish in similar areas of the USA, overlapping with the distribution of Schinus. However, the niche model predicted that only the Ouro Preto thrips could establish in the USA. The difference in model predictions suggests an apparent preadaptation of the Salvador thrips to lower temperatures than those experienced at the locations they were collected in Brazil. The Ouro Preto thrips had similar fecundity on two Florida Schinus haplotypes, whereas lower fecundity on haplotype A was found for the Salvador thrips. Based on these results, the Ouro Preto population may be better adapted to the climatic conditions and plant haplotypes found in Florida. Moreover, greenhouse studies indicated that Schinus growth was greatly reduced by thrips feeding, which may result in lower weed reproduction and densities in the field.

English

A field experiment was carried out at Tamil Nadu Agricultural University, Coimbatore during kharif seasons of 2010 and 2011 to study the effect of Glyphosate on weed management and grain yield in kharif maize of transgenic stacked and conventional maize hybrid. This investigation was conducted with the following objectives to evaluate the weed control efficiency and crop productivity with K salt of glyphosate formulations under field conditions. Treatments consisted of two transgenic stacked hybrids named 30V92 and 30B11 applied with glyphosate as early post emergence at 900 and 1800 g a.e ha-1 during kharif  season of 2010 and conventional maize hybrids named 30V92 and 30B11 applied with glyphosate by controlled droplet application method at 900, 1350 and 1800 g a.e ha-1 during kharif season of 2011 compared with non-transgenic counterpart maize hybrids applied with pre emergence atrazine at 0.5 kg ha-1 followed by one hand weeding on 40 days after sowing (DAS) with and without insect management. Among the treatments, early POE application of glyphosate at 1800 g a.e ha-1 registered lower weed density and higher weed control efficiency in transgenic and non-transgenic maize hybrids at all the intervals. Higher grain yield was registered with post emergence application of glyphosate at 1800 g a.e ha-1 in transgenic and non transgenic maize hybrid of 30V92 during both the kharif seasons   Key words: Glyphosate, transgenic maize, weed control efficiency, weed index, yield.

Tillage and Grazing Impact on Annual Crop Yields Following Conversion from Perennial Grass to Annual Crops

Interest in transitioning from perennial grasses to annual crops should increase because of renewed interest in including a perennial phase in annual crop rotations. Different tillage options for converting from perennial grasses to annual crops were evaluated at the Northern Great Plains Research Laboratory, USDA-ARS, in Mandan, ND. Previously, the study site evaluated intermediate wheatgrass [Thynopyrum intermedium (Host) Barkworth & D.R. Dewey] persistence when grazed at the early vegetative, mid-culm elongation, or late boot morphological stages. Soybeans [Glycine max (L.) Merr.] in 2005, corn (Zea mays L.) in 2006, flax (Linum usitatissimum L.) in 2007, and spring wheat (Triticum aestivum L.) in 2008 were seeded using either no-till (NT) or minimum till (MT). Tillage interacted with grazing history to impact soybean yields, total weed density in flax, and weedy grasses, such as green foxtail [Setaria viridis L. (Beauv.)], barnyardgrass [Echinochloa crus-galli L. (Beauv.)] and Kentucky bluegrass (Poa pratensis L.) in spring wheat. The use of NT generally resulted in greater yields and lower weed densities than MT, but even 4-years later, grazing still had an impact on weed populations. Our data suggest that producers should use NT rather than MT when converting from perennial grass to an annual cropping system.

Management of Weeds in Maize (Zea mays L.) through Various Pre and Post Emergency Herbicides

Field experiments were conducted in 2013 during main cropping season at Ambo and Guder to determine the effect of different post and pre emergency herbicides application on weed dynamics in maize (Zea mays L.) variety, BH-660 in randomized complete block design with three replications. Six treatments including Nicosulfuron (Arrow 75 WDG) at 0.09 kgha-1+ silwet gold (adjuvant) at 0.10%, S-metolachlor 290 + Atrazine (Primagram) at 3.00 kgha-1, s-metolachlor (dual gold) 1.5 kgha-1, hand weeding as standard check and weedy check as control were used. Effect of different herbicides on weed density was significant. The lowest weed density was recorded in plot treated with hand weeding and hoeing (3.12 m-2) followed by Nicosulfuron (18.67 m-2) and Primagram (3.88 m-2). But, the maximum was recorded in weedy check (14.16 m-2). However, no significant difference was observed between Nicosulfuron and Primagram. The minimum dry weight of weeds (0.77 gm-2) was observed in hand weeding and hoeing followed by Nicosulfuron which is not significantly different from s-metolachlor. Moreover, those treatments also significantly increased the yield and yield component of maize. This is an indication of the reliability and promise as well as the exhibition of the great potential of the Nicosulfuron is the effective control of the weeds and enhancing yield of maize in Guder and Ambo, Ethiopia.

Effect of critical period of crop-weed competition on nutrient content and uptake by weed and rabi castor (Ricinus communisL.)

A field experiment was conducted at Instructional Farm, N. M. College of Agriculture, Navsari Agricultural University, Navsari during rabi season in two consecutive years during 2010–11 and 2011–12 to study the effect of critical period of crop-weed competition on nutrient content and uptake by weed and rabi castor (Ricinus communis L.). The 12 treatments viz., weed free up to 30 DAS, weed free up to 60 DAS, weed free up to 90 DAS, weed free up to 120 DAS, weed free up to harvest, weedy up to 30 DAS, weedy up to 60 DAS, weedy up to 90 DAS, weedy up to 120 DAS, weedy up to harvest, two hand weedings and interculturing at 30 and 60 DAS and pendimethalin @ 1 kg/ha (as pre-emergence)+ one hand weeding and interculturing at 60 DAS were evaluated with three replications in a randomized block design (RBD). The results revealed that treatment weed free up to harvest recorded significantly lowest weed density, dry weight of weeds, nutrient uptake by weed and maximum in castor seed yield and nutrient uptake by plant followed by the treatment weed free up to 120 DAS and weed free up to 90 DAS. However, highest net monetary returns (Rs. 46.6 x 103/ha) and B: C ratio (3.02) were obtained with the treatment weed free up to 90 DAS which was found more critical period for crop weed competition.

Weed control in conservation agriculture systems of Zimbabwe: Identifying economical best strategies

Abstract Weed management under conservation agriculture (CA), especially when manually controlled is one of the major setbacks for the widespread adoption of CA in southern Africa. This study was conducted at three on-station and three on-farm sites: CIMMYT-Harare, Domboshawa Training Centre and Henderson Research Station (on-station sites), Hereford farm, Madziva communal area and Shamva communal area (on-farm sites). The evaluation focused on the effect of initial herbicide application and succeeding manual weeding whenever weeds were 10 cm tall or 10 cm in length for grasses with stoloniferous–rhizomatous growth habit. Weeds counts, weeding time and grain yields were collected at all on-station sites. At the on-farm sites, weed counts were done before weeding and a number of farmers were timed during weeding. The results showed that herbicides use reduced the weed density and time taken on weeding at all sites. Combining herbicides e.g. atrazine, glyphosate and metalachlor had the lowest weed density and weeding time at all sites. However, the treatments had no effect on maize grain yields suggesting that appropriate and timely manual weeding reduced crop/weed competition. Herbicides treatments had higher input costs than manual weeding due to the additional cost of herbicide but the treatment with manual weeding only had more overall labour days compared to the mixture of three herbicides. In order to achieve economic benefits, smallholder farmers may use the time for value addition e.g. expand cropped land area, use time for value addition, or sell new products on the market. Herbicides use reduces the manual labour needed to control weeds and minimise total crop failure due to untimely weeding hence, herbicides are an important but not the only weed control option under CA systems in Zimbabwe.

Weed Growth and Grain Yield, as Affected by Herbicides, in Dry-seeded Rice in Sri Lanka

Dry-seeded rice (Oryza sativa L.) is an emerging establishment system in irrigated areas in many Asian countries, including Sri Lanka. A field experiment was conducted in the major (Maha) 2011/12 and minor (Yala) 2012 seasons at the research farm of the Rice Research and Development Institute, Sri Lanka, to evaluate the efficacy of several herbicides in an irrigated dry-seeded rice system. Herbicide treatments included propanil, followed by MCPA (2-methyl-4-chlorophenoxyacetic acid), pendimethalin, oxadiazon plus propanil, oxyfluorfen, and pendimethalin, followed by fenoxaprop plus ethoxysulfuron, oxadiazon plus propanil, followed by fenoxaprop plus ethoxysulfuron, and oxyfluorfen followed by fenoxaprop plus ethoxysulfuron. The efficacy of herbicides varied across years. All herbicide-treated plots had lower weed density and weed biomass than the untreated plots. The results suggested that oxyfluorfen applied alone provided the poorest weed control. Generally, there was no effect of the additional spray of fenoxaprop plus ethoxysulfuron on weed biomass at 42 days after planting. However, grain yield was higher in the plots sprayed with the pre-emergence, followed by post-emergence herbicides, compared with the plots sprayed with only pre-emergence herbicide(s). The results suggest that different herbicide options are available in Sri Lanka to effectively control weeds in dry-seeded rice systems.

Impact of Hybrid Bluegrass and Tall Fescue Seeding Combinations on Brown Patch Severity and Weed Encroachment

Tall fescue (Festuca arundinacea) and hybrid bluegrass (Poa pratensis L. × Poa arachnifera) can both be successfully grown in the transition zone of the United States. However, each grass has limitations. Tall fescue is susceptible to the fungal pathogen Rhizoctonia solani, whereas slow establishment and susceptibility to weed infestations limit hybrid bluegrass. Previous studies have shown the benefits of combining kentucky bluegrass with tall fescue in seeding mixtures. Research was conducted to evaluate the impact of two seeding combinations of hybrid bluegrass and tall fescue (one combination seeded at a 1.9:1 seed count ratio favoring tall fescue, the other combination seeded at a 1:1.8 seed count ratio favoring hybrid bluegrass) as well as monocultures of the species on turfgrass cover, weed species infestation, brown patch disease severity caused by R. solani, sod strength and species ecology. The seeding combinations had lower weed density during establishment and greater turf cover than the monoculture of hybrid bluegrass. The monoculture of tall fescue was subjected to more brown patch disease than the seeding combinations during and after the first year of establishment. Brown patch infestations likely reduced tall fescue cover and led to a species shift favoring hybrid bluegrass in the seeding combinations based on tiller count and weight data. Seeding combinations of tall fescue and hybrid bluegrass are beneficial from an epidemiological perspective because they reduce disease and weed infestations compared with monocultures of either species. From an agronomic perspective, the seeding combination favoring tall fescue provided the densest turf, whereas the seeding combination favoring hybrid had the greatest sod strength. Chemical name used: clopyralid (3,6 dichloropyridine-2 carboxylic acid)