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Efficacy and Phytotoxicity of Different Rates of Oxadiargyl and Pendimethalin in Dry-seeded Rice (oryza Sativa L.) in Bangladesh

Sharif Ahmed
International Rice Research Institute, Los Ba~nos, Philippines

Bhagirath Singh Chauhan
Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland, Toowoomba 4350, Queensland, Australia

Abstract/ Executive Summary:

A field study was established to evaluate oxadiargyl and pendimethalin during the wet seasons in Bangladesh in 2012 and 2013. The study evaluated the following treatments: oxadiargyl applied at 80,120, and 160 g ai ha1; pendimethalin at 800, 1200, and 1600 g ai ha1; partial weedy; and weed-free. Rice plant density was greatly affected by weed control treatment. Lower density and lower uniformity of the rice plant stand occurred as a result of increased rates of herbicides. Increased rates of pendimethalin were more toxic than increased rates of oxadiargyl. Both herbicides effectively controlled Digitaria ciliaris, Echinochloa colona, and Phyllanthus niruri; however, they were unable to control Murdannia nudiflora. Oxadiargyl controlled Cyperus rotundus across rates by 31-55%, but pendimethalin was completely ineffective on it, and higher rates of both herbicides had no effect in controlling this weed. Both herbicides at higher rates reduced total weed biomass significantly. Among herbicide treatments, the highest yield (3.7-4.0 t ha1) was recorded in plots treated with oxadiargyl at 160 g ai ha1and the lowest yield (2.4-2.8 t ha1) was in plots treated with pendimethalin at 1600 g ai ha1. Results from our study suggest that a higher rate of oxadiargyl can increase yield by suppressing weeds in dry-seeded rice systems. Similar to the results of oxadiargyl, pendimethalin at higher rates also greatly suppressed weeds; however, yield decreased due to phytotoxicity to rice seedlings.

Keywords: Herbicide rate, Plant density, Plant injury, Weeds density, Weed biomass, Rice yield

Location:

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Commodity: Rice

Objectives:

This study was established to evaluate the comparative performance of oxadiargyl and pendimethalin at different rates on weed control and crop response in dry-seeded rice systems.

Methodology:

Full doses of TSP, MoP, gypsum, and zinc sulphate were applied immediately before sowing. Urea was applied in four equal splits at14 DAS, at active tillering (30 DAS), at maximum tillering (45 DAS), and at panicle initiation (65 DAS). Immediately after sowing, the field was surface irrigated. After this, irrigation was based on tensiometer readings using a threshold value of 15 kPa at 15-cm soil depth. At each irrigation, a 5 cm floodwas established. At 50 DAS, the fungicide tebuconazole plus tri-floxystrobin 300 g ai ha1 (Nativo 75 WP, Bayer Crop Science Limited, Bangladesh) was applied to control blast, and fipronil 3G300 g ai ha1(Regent 3 GR, BASF Bangladesh Limited) was applied at 70 DAS to control stem borers. To evaluate herbicide phytotoxicity in rice, rice plants were counted at 14 DAS from four randomly selected 1-m row lengths in each plot and the reduction (%) in plant stands was calculated by comparing with the non-treated check. The non-uniformity of plant establishment due to herbicide toxicity was determined as the coefficient of variation of means of the 12 rows (4 rows 3 replicates) for each treatment combination. To evaluate the performance of herbicides on individual weed species, weed density and weed biomass were measured at 40 DAS by randomly placing two quadrats, measuring 40 cm by 40 cm, in each plot. Weeds were separated by species, counted, and their biomass was measured after oven drying the samples at 7⁰C for 72 h. To evaluate the effect of weeds on rice, weed and rice biomass were measured from two 40 cm by 40 cm quadrats at 50% flowering. At harvest, rice panicles were counted from four randomly placed 1-m row lengths in each plot. Rice grain yield was determined from a harvested area of 4.0 m 2.2 m. Grain yield was converted to t ha1at 14%moisture content. Data were analyzed using analysis of variance (ANOVA) to evaluate differences between treatments, and means were separated using the least significant difference (LSD) at 5% (Crop Stat7.2; International Rice Research Institute, Philippines). In a combined analysis of data, the interaction between years and treatments was significant; therefore, the data were presented separately for each year. Weed density and biomass data were transformed using square root transformation [√(xþ0.5)] before analysis. Transformation, did not improve homogeneity. Therefore,the original values were used for analysis and presentation.

Source of Information: Crop Protection 72 (2015) 169e174

Article Link (Online Journal):

Funding Source:

1.

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Total Budget (Tk.) :

Achievement/Findings:

In this study, we used oxadiargyl and pendimethalin at recommended and higher rates. The objective was to assess the benefits and risks of higher rates of pre-emergence herbicides, which might be helpful in cautioning and making recommendations for farmers who grow dry-seeded rice. However, in this study, we did not use any rate of herbicides lower than the recommended rate, and did not consider cost-effectiveness. But, for farmers, cost-effectiveness is very important. Therefore, further research is needed to evaluate the economics of pre-emergence herbicides at different rates indifferent soil and environmental conditions.

Knowledge Management: Journal