Weedy Plots Research Articles

Effect of weed management techniques on weeds, yield and economics on rice based cropping systems

ABSTRACT :A field experiment was conducted at the Agronomy Research Farm of Narendra Deva University of Agriculture and Technology, Kumarganj, Faizabad (U.P.) during two consecutive crop seasons of 2008-09 and 2009-10. The experiment was laid out in Split Plot Design with three replications. The twelve treatment combinations comprised of six cropping systems viz., rice-wheat, rice-chickpea, rice-fieldpea, rice-mustard, rice-linseed, rice-berseem, were kept in main plots and two weed control treatments viz., two hand weeding (20 and 40 DAS) and weedy check in rice crop and one hand weeding at 30 DAS and weedy in Rabi crops were kept in sup- plots. The hand weeding was done with the help of Khurpi. In rice crop lower weed density was recorded in rice-chickpea cropping system followed by rice-wheat cropping system at all the stages of crop growth during both the years. Significantly lower weed dry weight was recorded in rice-mustard cropping system as compared to other cropping system at all the stages of crop growth during both the years. Application of 2 HW (20 and 45 DAS) gave highest grain yield of 44.42 q /ha-1 in rice- berseem cropping system during first year and 43.40q/ ha-1 in rice-chickpea during second year. The lowest grain yield of 12.32 and 14.30 q / ha-1 was obtained in weedy plot of rice-fieldpea cropping system during respective years. In Rabi crops significantly lower weed density and dry weight was recorded in one hand weeding compared to weedy check plot at all the stages of crop growth during both the years.

The Effect of herbicides and Agriculture spacing, on yield components of wheat Triticum aestivum L. and on accompanied weeds

A field experiment was conducted at the farmer field near Ramadi city /Al-Anbar governorate during the growing season of 2007-2008 to investigate the effect of herbicides and row spacing on weeds accompanied with wheat and on growth characteristics , grain yield and yield components of wheat . The factorial experiment was carried out according to RCBD design with three replication . Two herbicides were included Pyroxsulam and Chevalier at rate of 0.3 L. ha-1, 0.3 kg ha-1 respectively. The bread wheat was planting at three row spacing 15, 20, 25 cm. Results showed great effect of herbicides in controlling weeds. The dry weight of weeds decreased in a percentages of 98.9% and 98.5% with Pyroxsulam and Chevalier respectively as compared with the weedy plots. While the grain yield of wheat increased in the same herbicides treatments. There was non significant deference between herbicides and hand weeding in almost all of the studied characters. The row spacing of 15 cm caused significant reduction in the dry weights of weed with 17. 36 gm.m-2 as compared with 20 and 25 cm with 19.71and 25.03 gm. m-2 respectively. However, row spacing of 25 cm was superior in number of spike. m-2, weight of 1000 grain and wheat yield which reached to 36.6 cm2, 406.04 spike . m-2, 46.6 gm and 5.3 t. ha-1 respectively. The results also showed the positive interaction between the herbicides and row spacing in decreasing the dry matter of weed that grown with the crop. The treatment of 25cm row spacing with Chevalier application gave grain yield of 6.36 t/ha with an increase percentage reached to 57.7% compared to 2.69 t. ha-1 recorded for the same raw spacing with no herbicide application .

Efficacy of azimsulfuron against complex weed flora in transplanted rice (Oryza sativa) under rainfed shallow lowland

A field experiment was conducted during the wet seasons of 2010 and 2011 at ICAR-National Rice Research Institute, Cuttack to study the efficacy of azimsulfuron for controlling broad spectrum of weeds in transplanted rice (Oryza sativa L.) field under rainfed shallow lowland. The present study consisted of 10 treatments which includes seven doses of azimsulfuron, viz. 12.5, 17.5, 22.5, 27.5, 30.0, 35.0 and 40 g/ha each with 0.2% surfactant along with recommended herbicide, pretilachlor at 625 g/ ha, weed-free and weedy as check. Yield attributes of rice were significantly (P<0.05) affected by weed control treatments. The highest grain yield (5.72 tonnes/ha) and N-use efficiency (57.2) were obtained in weed free check, realizing 76% increase in grain yield of rice over weedy check. Azimsulfuron at 35 and 40 g/ha applied 18 days after transplanting was found to be very effective (weed control efficiency 92.8 and 95.5%, respectively) in controlling the complex weed flora and produced comparable grain yield with weed-free check. There was more than 45% reduction in the grain yield of rice due to competition with weeds in weedy plots. The negative effect of weed competition in weedy check plot was reflected in significant reduction in crop growth rate (4.66 g/m2/day) and total biomass of rice (6.89 tonnes/ha).

Weed management in rice under SRI method of crop establishment

A field experiment was conducted during dry seasons of 2011 and 2012 at the ICAR-National Rice Research Institute, Cuttack to study the weed spectrum and efficacy of different weed management practices under system of rice intensification (SRI). Cyperus difformis (23.1%) was the predominant weed flora followed by Echinochloa colona (14.7%) at 45 days after transplanting (DAT) in weedy plots. Management of weeds by operating cono weeder at 15 and 30 DAT was found most effective practice (weed control efficiency 90.8% at 45 DAT) for controlling broad spectrum of weeds and realizing higher grain yield (5.79 t/ha). However, chemical weed control by applying azimsulfuron at 35 g a. i./ha applied 15 DAT was the most economic weed management option for getting higher net returns (Rs. 34, 400/ha) and benefit: cost ratio (2.82). Application of azimsulfuron also showed least energy input (8.6 x 103 MJ/ha) compared with all other weed management treatments.

Efficacy and economics of different herbicides, their weed species selectivity, and the productivity of mechanized dry-seeded rice

A field study was conducted in 2012 and 2013 at the International Rice Research Institute (IRRI) farm in Los Baños, Philippines, to evaluate the economic performance of PRE oxadiazon and pendimethalin, early POST butachlor plus propanil and thiobencarb plus 2,4-D, and late POST herbicides bispyribac-sodium and fenoxaprop plus ethoxysulfuron applied solely or sequentially. All herbicide treatments with PRE or early POST herbicides reduced total weed density by 85–100% and biomass by 80–100%, whereas late POST treatments reduced weed density by 32–50% and biomass by 40–62% compared with the nontreated weedy check. The highest grain yield was achieved in weed-free plots (5.9–6.1 t ha−1) and the lowest in weedy plots (0.2 t ha−1). Among the herbicide treatments, rice treated with oxadiazon, thiobencarb plus 2,4-D, and butachlor plus propanil followed by the late POST herbicides had grain yield increments of 23–25, 20 to 26, and 18 to 23 times that of the yield in weedy plots, respectively. The economic analysis showed that the sole application of oxadiazon provided the highest net profit and benefit-cost ratio in both years, which was similar to the treatments involving oxadiazon or early POST herbicides, followed by the sequential application of late POST herbicides.

Management of Rottboellia cochinchinensis and other weeds through sequential application of herbicides in dry direct-seeded rice in the Philippines

Dry direct-seeded rice (DSR) systems are becoming popular due to resource conservation and economic returns but high weed pressure limits rice productivity. Rottboellia cochinchinensis (Lour.) W. D. Clayton is an emerging noxious weed of DSR and requires a suitable herbicide package for effective control. A field study was conducted to evaluate the efficacy of two pre-emergence (oxadiazon and pendimethalin) and two post-emergence (cyhalofop and bentazon) herbicides used in various combinations and sequences during two consecutive seasons (dry season, 2013–14 and wet season, 2014) at the International Rice Research Institute (IRRI), Los Baños, Philippines. Experiments were laid out in a randomised complete block design with three replications. Weedy plots were kept as control. All the herbicide treatments significantly reduced density and biomass of R. cochinchinensis and other dominating weeds at the flowering stage of rice during both seasons. The best treatment was pendimethalin followed by bentazon + cyhalofop, which caused 88–91% reductions in R. cochinchinensis density over the weedy control (9.4–13.0 plants m−2) during both seasons. It also reduced R. cochinchinensis biomass by 98–99% over the weedy control (331–344 g m−2). Different herbicide sequential treatments also controlled density and biomass of Cyperus rotundus L., Eclipta prostrata L., Echinochloa colona (L.) Link, and Murdannia nudiflora (L.) Brenan over the weedy control. Highest reductions in total weed density (82–84%) and total weed biomass (95–97%) over the weedy control were observed from pendimethalin followed by bentazon + cyhalofop applications during both seasons. All the herbicide treatments increased rice grain yield significantly over the control. The maximum grain yield was obtained from pendimethalin followed by bentazon + cyhalofop applications, which was 4.7 and 3.0 t ha−1 during the dry season, 2013–14 and the wet season, 2014, respectively. The results suggest that the pre-emergence application of pendimethalin followed by the combination of post-emergence herbicides (bentazon and cyhalofop) may control R. cochinchinensis and other noxious weeds in DSR effectively with subsequent increment in rice grain yield.

RNAseq reveals weed-induced PIF3-like as a candidate target to manipulate weed stress response in soybean.

Weeds reduce yield in soybeans (Glycine max) through incompletely defined mechanisms. The effects of weeds on the soybean transcriptome were evaluated in field conditions during four separate growing seasons. RNASeq data were collected from six biological samples of soybeans growing with or without weeds. Weed species and the methods to maintain weed-free controls varied between years to mitigate treatment effects, and to allow detection of general soybean weed responses. Soybean plants were not visibly nutrient- or water-stressed. We identified 55 consistently downregulated genes in weedy plots. Many of the downregulated genes were heat shock genes. Fourteen genes were consistently upregulated. Several transcription factors including a PHYTOCHROME INTERACTING FACTOR 3-like gene (PIF3) were included among the upregulated genes. Gene set enrichment analysis indicated roles for increased oxidative stress and jasmonic acid signaling responses during weed stress. The relationship of this weed-induced PIF3 gene to genes involved in shade avoidance responses in Arabidopsis provide evidence that this gene may be important in the response of soybean to weeds. These results suggest that the weed-induced PIF3 gene will be a target for manipulating weed tolerance in soybean.

Effect of crop establishment methods and weed control treatments on weed management, and rice yield

Lower water availability coupled with labor shortage has resulted in the increasing inability of growers to cultivate puddled transplanted rice (PTR). A field study was conducted in the wet season of 2012 and dry season of 2013 to evaluate the performance of five rice establishment methods and four weed control treatments on weed management, and rice yield. Grass weeds were higher in dry-seeded rice (DSR) as compared to PTR and nonpuddled transplanted rice (NPTR). The highest total weed density (225–256plantsm−2) and total weed biomass (315–501gm−2) were recorded in DSR while the lowest (102–129plantsm−2 and 75–387gm−2) in PTR. Compared with the weedy plots, the treatment pretilachlor followed by fenoxaprop plus ethoxysulfuron plus 2,4-D provided excellent weed control. This treatment, however, had a poor performance in NPTR. In both seasons, herbicide efficacy was better in DSR and wet-seeded rice. PTR and DSR produced the maximum rice grain yields. The weed-free plots and herbicide treatments produced 84–614% and 58–504% higher rice grain yield, respectively, than the weedy plots in 2012, and a similar trend was observed in 2013.

Critical Periods of Weed Control for Naked Crabgrass (Digitaria nuda), a Grass Weed in Corn in South Africa

Difficulties in chemically controlling large crabgrass in corn in South Africa have recently been attributed to the occurrence of naked crabgrass. In contrast to large crabgrass, naked crabgrass is not easily controlled with acetanilide herbicides. Critical periods of weed control (CPWC) for naked crabgrass in corn was determined in field studies during the 2009/2010 and 2010/2011 growing seasons at two separate localities for an early and late planting date of corn. Weed-free and weed–crop interference treatments of increasing duration were maintained at various crop growth stages in the presence of naked crabgrass. Biomass of naked crabgrass was determined as dry weight per square meter quadrant, which yielded 428 g m−2at Potchefstroom and 594 g m−2at Wesselsbron. An exponential regression model was used to determine the CPWC expressed as growing degree days after crop emergence, on the basis of an estimated 10% relative yield loss in corn. The onset and ending, as well as the duration of the CPWC, differed between seasons and localities. At 10% relative yield loss, the onset of the CPWC ranged between the two-leaf (V2) and six-leaf (V6) stages, and the ending between the 12-leaf (V12) stage and 2 wk after tasseling (T + 2). The duration of the CPWC ranged between 22 and 80 d for the respective planting dates, years, and localities. Yield losses ranged from 28 to 82% in the season-long weedy plots. The shifting of planting dates alone did not reduce yield losses since the effect of late infestations of naked crabgrass is significant. Naked crabgrass control from crop emergence is essential, followed by POST herbicide application during the critical period of weed control to lower the risk of corn yield losses.

Effects of irrigation and weed-control methods on growth of weed and rice.

A field experiment was conducted to study the effects of weeds control methods and an irrigation model on rice growth as well as water consumption and weed quantity in the paddy field. In conventional paddy rice production, one of the most important irrigated crops, a significant amount of irrigation water is lost due to percolation and evaporation. A new irrigation model called the Rain-Catching and Controlled Irrigation (RCCI) model has been developed as a viable water-saving technology in the production of paddy rice. In this study the performance of the RCCI model has been analyzed under mulching, hand weeding and weedy conditions in Jiangsu Province of China. The experiment was laid out in Randomized Complete Block Design (RCBD) with three replications and nine treatments. The three replicates consisted of three water management regimes: high dry high flooding (HD-HF), high dry low flooding (HD-LF), and shallow and frequent irrigation (SF) water treatment. The RCCI model was adopted in HD-HF and HD-LF while Flooding Irrigation (CFI) was adopted in SF as a control. The nine treatments were equally divided under mulching, hand weeding and weedy conditions. The lowest and maximum irrigation water delivery was 244.86 mm in mulching and 429.22 mm in hand weeding, respectively at HD-HF. And the lowest and maximum irrigation water delivery was 300.1 mm in the mulching field and 680.72 mm under hand weeding, respectively at HD-LF. The Nanjing 44 rice variety was used. It was observed that weed density and dry weight were significantly influenced by the amount of irrigation water in all the mulching, hand weeding and weedy plots. Considering yield and the number of irrigations, the RCCI model produced better results than CFI. Mulching under RCCI was an effective method to control weeds and reduce labor cost. In addition, mulching decreases the use of herbicides and the risk of pollution. On the other hand, mulching could improve yield and save water. Keywords: irrigation, weed control, mulching, hand weeding, RCCI, weed population, agronomy traits, paddy rice DOI: 10.3965/j.ijabe.20140705.003 Citation: Towa J J, Guo X P. Effects of irrigation and weed-control methods on growth of weed and rice. Int J Agric & Biol Eng, 2014; 7(5): 22－33.

Weed population dynamics, herbicide efficacies, and crop performance in a sprinkler-irrigated maize-rice cropping system

In the future, maintaining food security will require an increase in rice productivity with less land, labor, and water. Agronomic approaches to reducing the water and labor demands of rice-based cropping systems include crop diversification to include crops with higher water productivity, direct-seeded rice, and irrigation scheduling based on soil water potential or alternate wetting and drying cycles. However, weeds are a major constraint to increasing rice productivity in these systems. A two-year study was conducted to identify the changes in weed population and to evaluate the efficacy of herbicides and their effect on crop performance in a sprinkler-irrigated maize-rice cropping system. The dominance of weed species shifted from a grass weed Echinochloa colona to broadleaved weeds, such as Hedyotis corymbosa, Lindernia spp., and Murdannia nudiflora. At 41 days after sowing (DAS) and at tasseling stage, glyphosate application provided a 90–100% decrease in total weed biomass of maize. The combined effects of all the herbicides applied in rice provided almost 100% control in total weed biomass at 40 DAS. However, the herbicide schedule in the cropping system was ineffective in controlling M. nudiflora. The weed control treatments had no significant effect on the yield of maize [8.7 and 11.5 (herbicide-treated) and 8.4 and 12.0 (partially weedy) Mgha−1 in 2012 and 2013, respectively], but rice grain yield was influenced significantly. Rice grain yield in herbicide-treated plots in 2012 and 2013 were more than 1.5 and 8.5 times greater than yield achieved in the weedy plots, respectively. A significant negative relationship was found between rice grain yield and weed biomass in both years. Future research in maize-rice cropping systems should focus on the integration of appropriate agronomic practices with herbicide rotation to ensure that weed management strategies are sustainable and effective, and to avoid the risk of herbicide resistance developing in weed populations.

Performance of Different Herbicides in Dry-Seeded Rice in Bangladesh

A field study was conducted in the boro season of 2011-12 and aman season of 2012 at Jessore, Bangladesh, to evaluate the performance of sequential applications of preemergence herbicides (oxadiargyl 80 g ai ha−1, pendimethalin 850 g ai ha−1, acetachlor + bensulfuranmethyl 240 g ai ha−1, and pyrazosulfuron 15 g ai ha−1) followed by a postemergence herbicide (ethoxysulfuron 18 g ai ha−1) in dry-seeded rice. All evaluated herbicides reduced weed density and biomass by a significant amount. Among herbicides, pendimethalin, oxadiargyl, and acetachlor + bensulfuranmethyl performed very well against grasses; pyrazosulfuron, on the other hand, was not effective. The best herbicide for broadleaf weed control was oxadiargyl (65–85% control); pendimethalin and acetachlor + bensulfuraonmethyl were not effective for this purpose. The best combination for weed control was oxadiargyl followed by ethoxysulfuron in the boro season and oxadiargyl followed by a one-time hand weeding in the aman season. Compared with the partial weedy plots (hand weeded once), oxadiargyl followed by ethoxysulfuron (4.13 t ha−1) provided a 62% higher yield in the boro season while oxadiargyl followed by a one-time hand weeding (4.08 t ha−1) provided a 37% higher yield in the aman season.

Response of Rice Genotypes to Weed Competition in Dry Direct-Seeded Rice in India

The differential weed-competitive abilities of eight rice genotypes and the traits that may confer such attributes were investigated under partial weedy and weed-free conditions in naturally occurring weed flora in dry direct-seeded rice during the rainy seasons of 2011 and 2012 at Ludhiana, Punjab, India. The results showed genotypic differences in competitiveness against weeds. In weed-free plots, grain yield varied from 6.6 to 8.9 t ha−1 across different genotypes; it was lowest for PR-115 and highest for the hybrid H-97158. In partial weedy plots, grain yield and weed biomass at flowering varied from 3.6 to 6.7 t ha−1 and from 174 to 419 g m−2, respectively. In partial weedy plots, grain yield was lowest for PR-115 and highest for PR-120. Average yield loss due to weed competition ranged from 21 to 46% in different rice genotypes. The study showed that early canopy closure, high leaf area index at early stage, and high root biomass and volume correlated positively with competitiveness. This study suggests that some traits (root biomass, leaf area index, and shoot biomass at the early stage) could play an important role in conferring weed competitiveness and these traits can be explored for dry-seeded rice.

Weed Management in Dry-Seeded Fine Rice under Varying Row Spacing in the Rice-Wheat System of Punjab, Pakistan

Direct seeding can curtail water and labor inputs involved in rice production; nevertheless, its large-scale adoption is impeded by heavy weed infestation. A field study was undertaken in 2011 and 2012 to evaluate the effects of crop row spacing (20 and 10 cm) and postemergence herbicides on weed growth and yield of dry-seeded rice. As a herbicide, pyrazosulfuron ethyl at 30 g ha–1, bispyribac-sodium at 30 g ha–1, or penoxsulam at 15 g ha–1 was applied (15 days after sowing, DAS) alone or in combination with fenoxaprop-p-ethyl at 86.25 g ha–1 subsequently (30 DAS). In addition, a partial weedy plot (manually weeded once at 28 DAS), and a weed-free plot were established for each row spacing In the partial weedy plot with 10-cm row spacing, the weed density was only 21 and 25% lower than that in the plot with 20-cm row spacing in 2011 and 2012, respectively. The sole application of an early postemergence herbicide restricted weed growth, while subsequent application of fenoxaprop as late postemergence application suppressed weed growth further, the magnitude of suppression being more pronounced in the plot with narrow row spacing. The density and biomass of weeds were lowest in the plot with 10-cm row spacing applied bispyribac-sodium followed by fenoxaprop . Under weed-free conditions, yields were 29% higher in the plot with 10-cm row spacing (4.18 t ha–1) than in that with 20-cm row spacing (3.23 t ha–1). Grain yield in the herbicide-treated plots was 87 – 188% higher than that in the partial weedy plots. These results suggested that narrow row spacing and sequential herbicide application can help tackle recalcitrant weed flora in dry-seeded rice fields.

Effect of tillage systems, seeding rates, and herbicides on weed growth and grain yield in dry-seeded rice systems in the Philippines

In Asia, dry-seeded rice (DSR) production systems are increasing because of water and labour scarcities. DSR can be sown under zero-till (ZT) or after conventional tillage (CONT) operations. In these seeding systems, however, weeds are the main biological constraint. A study was conducted during the wet season of 2012 and the dry season of 2013 at the International Rice Research Institute to evaluate the effect of the tillage systems (ZT and CONT), seeding rate [low seeding rate (LSR) at 50 kg ha−1, and high seeding rate (HSR) at 100 kg ha−1], and weed control treatments (oxadiazon applied as pre-emergence, oxadiazon applied as pre-emergence followed by a commercial mixture of fenoxaprop + ethoxysulfuron as post-emergence at 21–24 days after sowing, and weedy) on weed growth and grain yield in DSR systems. The efficacy of herbicides 14 days after the application of post-emergence herbicide was similar between the tillage systems and between seeding rates. At crop harvest, weed biomass was higher in the ZT plots than in the CONT plots, and higher at LSR than at HSR. At the same time, herbicide applications decreased weed biomass by 73–96%, compared with the weedy plots. Compared with the ZT plots, CONT plots had 9–18% higher grain yield. Similarly, plots sown at HSR had 17–19% higher grain yield than at LSR. Weedy plots had 81–84% less yield than the herbicide-treated plots (3060–3380 kg ha−1 in the wet season and 5820–5950 kg ha−1 in the dry season).

Increasing Crop Rotation Diversity Improves Agronomic, Economic, and Environmental Performance of Organic Grain Cropping Systems at the USDA‐ARS Beltsville Farming Systems Project

Increasing Crop Rotation Diversity Improves Agronomic, Economic, and Environmental Performance of Organic Grain Cropping Systems at the USDA‐ARS Beltsville Farming Systems Project

Competition for Nutrients between Cold-Tolerant Maize and Weeds

Maize is a significant crop in Hungary, cultivated on about 1.3–1.5 million ha, approximately 25% of the total arable land. Dense weed infestation of maize can result in significant yield reduction because of the competition for water and nutrients. Adequate fertilization is an important factor for the development of maize but it also enhances weeds growth. Therefore, strong competition for nutrients can occur between the crop and weeds. Recently, hybrid maize, which is tolerant to the cold weather, has been introduced in Hungary. In a field experiment, we assessed the weed cover, development of the weeds, and the rate of the infestation of weeds in competition with this cold-tolerant hybrid. The field trial was conducted in 2010 in Hungary, Zala County, close to the town of Keszthely in field conditions with plot size of 0.1 ha in four replicates. Plant samples were taken from crop and weeds at different intervals of growth. The fresh weight, dry biomass, and nutrient content of maize and weeds were measured. The early development of weeds was very dynamic and strong in the cold-tolerant maize cultures. On the 12th week after sowing, the maize biomass was 64% less than the weed-free maize as a result of the competition. Threefold difference was found in the biomass production of maize between the weedy and the weed-free experimental plots. The difference in potassium (P) content was also similar to that of the biomass production. The P content of maize was 3.17 times greater and the calcium (Ca) content was 3.24 times greater in samples collected from weed-free areas. The biggest difference was observed in the case of nitrogen (N) content. It was 4.73 times greater in the weed-free maize than in the weedy plots. This result shows that the competition for N was very strong between the maize and the weeds.

Effects of different irrigation intervals and weed control on yield and yield components of safflower (Carthamus tinctorius L.)

A two-year (2008–2009) field experiment was conducted to determine the effect of irrigation management and weed control on yield and yield components of safflower. The experiment was conducted as a split-split plot arranged in a randomized blocks design with three replications. There were two treatments (weedy and weed free) and four irrigation interval water managements (7 days for all stages, 15, 22 and 28 days after six-leaf stages). The results indicated that grain yield was 29% higher in weed-free plots than in weedy plots. Weed competition reduced yield components such as primary branches, petal weight and number of capitulum per plant. Increasing the irrigation interval to 15 days at the six-leaf stage had no significant effects on grain yield, but grain yield decreased by 18 and 29.8% with increases in the irrigation interval to 22 and 28 days, respectively. An increased irrigation interval >15 days had negative effects on yield components like number of capitulum per plant, petal weight and number of primary branches. The highest grain yield (3703 kg ha−1) was obtained in the weed-free plot, and there was no significant difference between 7- and 15-day irrigation intervals.

Effect of Turnip Soil Amendment and Yellow Nutsedge (Cyperus esculentus) Tuber Densities on Interference in Polyethylene-Mulched Tomato

Yellow nutsedge is a problematic weed in polyethylene-mulched tomato production. Soil fumigation with methyl bromide is the most effective method of controlling nutsedges, but because of ozone depletion, the phase-out of methyl bromide has complicated nutsedge control in polyethylene-mulched tomato and other vegetable crops. Plants belonging to the Brassicaceae family produce glucosinolates, which upon tissue decomposition generate biocidal isothiocyanates and therefore can be used as a biological alternative for yellow nutsedge control. Field experiments were conducted in 2007 and 2009 to study the influence of soil amendment with ‘Seventop’ turnip cover crop on the interference of yellow nutsedge planted at 0, 50, and 100 tubers m−2in raised-bed polyethylene-mulched tomato production. There was no advantage of soil amendment with Seventop on reducing yellow nutsedge interference in polyethylene-mulched tomato. Regardless of soil amendment, increasing initial tuber density from 50 to 100 tubers m−2increased yellow nutsedge shoot density, shoot dry weight, and tuber production at least 1.7, 1.6, and 1.6 times, respectively. As a result, tomato canopy width, shoot dry weight, and marketable yield decreased with increasing initial tuber densities. However, increased tuber density had minimal impact on tomato height. Relative to weed-free plots, interference of yellow nutsedge at 50 and 100 tubers m−2reduced marketable yield of tomato up to 32 and 49%, respectively. Shading of the middle and lower portion of tomato plants by yellow nutsedge shoots could be the major factor for reducing tomato growth and yield in weedy plots. It is concluded that soil amendment with Seventop turnip is not a viable option for reducing yellow nutsedge interference at 50 and 100 tuber m−2in polyethylene-mulched tomato.

Use of13C Isotope Discrimination Analysis to Quantify Distribution of Barnyardgrass and Rice Roots in a Four-Year Study of Weed-Suppressive Rice

In a 4-yr field study, “weed suppressive” rice cultivars provided 30% greater control of barnyardgrass and sustained 44% less yield loss (relative to weed-free) compared to “nonsuppressive” tropical japonica rice cultivars.13C analysis revealed that rice root mass predominated vertically and laterally within the soil profile of plots infested with barnyardgrass. Among all cultivars, rice roots accounted for 75 to 90% of the total root mass in samples, and this was most concentrated in the surface 5 cm of soil in the row. Barnyardgrass roots were most prevalent in the surface 5 cm between rows where they accounted for 30% of total root mass. Overall, barnyardgrass root mass was about twice as high in nonsuppressive rice compared to suppressive rice. Weed suppression by indica/tropical japonica rice crosses generally was intermediate between that of the other two rice groups. At the 0- to 5-cm depth, between-rows, barnyardgrass root mass was correlated negatively with rice height (r = −0.424), yield (r = −0.306), and weed control ratings (r = −0.524) in weedy plots. Control ratings in weedy plots also were negatively correlated with rice percent height reduction (r = −0.415) and % yield loss (r = −0.747) relative to weed-free plots, and with barnyardgrass root mass as a percent of total root mass (r = −0.612). Control ratings were positively correlated with rice yield under weed pressure (r = 0.429) but were correlated with rice root mass in-rows only (r = −0.322). Clearly, rice root mass could not have been the major cause of the differences in barnyardgrass control between cultivars.