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Sensitivity of Annual Weeds Against Metolachlor+ Bensulfuron-methyl Herbicide in Transplanted Rice

M. K. A. Bhuiyan*
Agronomy Division, Bangladesh Rice Research Institute (BRRI), Gazipur, Bangladesh

M. M. Mahbub
Agronomy Division, Bangladesh Rice Research Institute (BRRI), Gazipur, Bangladesh

M. Z. I. Baki
Agronomy Division, Bangladesh Rice Research Institute (BRRI), Gazipur, Bangladesh

Abstract/ Executive Summary:

Field trials were conducted at Bangladesh Rice Research Institute (BRRI), Gazipur during aman, 2014 and boro, 2014-15 to evaluate the efficacy of metolachlor + bensulfuron methyl 20% WP on weed suppression of transplanted rice. Metolachlor + bensulfuron methyl 20% WP @ 150, 190 and 230 g ha^-1 were applied and pyrazosulfuran ethyl @ 125 g ha^-1, weed free and unweeded control were the treatment variables. Visual observations indicated that this herbicide possesses high selectivity and not toxic to rice plants. The results revealed that the major weed flora associated with the transplanted rice was mainly comprised of two grasses, two sedges and three broadleaf in aman and two grasses, two sedges and two broadleaf in boro season. The most dominant weeds were Cyperus difformis, Echinochloa crus-galli, Scirpus maritimus and Monochoria vaginalis in both the growing seasons. Application of metolachlor + bensulfuron methyl 20% WP @ 190 g ha-1 was most effective to suppress weeds in both the seasons resulting in increased grain yield more than 40% as compared to unweeded control. Therefore, metolachlor + bensulfuron methyl 20% WP@ 190 g ha^-1 applied at one to two leaf stage of weed effectively controls the weed infestation in transplanted rice.

Keywords: Metolachlor + bensulfuron methyl, Transplanted rice, Annual weed, Weed control

Location: At Bangladesh Rice Research Institute (BRRI), Gazipur

Start Date: 00-00-2014

End Date: 00-00-2015

Program Area: Pest Management

Commodity: Herbicide

Objectives:

To evaluate the efficacy of metolachlor + bensulfuran methyl for rice weed suppression and find out an appropriate dose of the herbicide and its impacts on transplanted rice.

Methodology:

The experiments were conducted at the Bangladesh Rice Research Institute, Gazipur, situated at 23059´33´´ N and 90024´19´´ E at an elevation of 8.4 m from the mean sea level, and is characterized by sub-tropical climate during aman, 2014 and boro, 2014-2015 seasons. The soil of the experimental site was non-calcareous dark grey floodplain with pH around 6.2 and low in organic matter (1.2%). The experiment was carried out with six (6) treatments viz. T1= Metolachlor + bensulfuran methyl 20% WP@ 150gha^-1 (7.5 g a.i. ha^-1), T2= Metolachlor + bensulfuran methyl 20% WP @ 190 g ha^-1(9.5 g a.i. ha^-1), T3= Metolachlor + bensulfuran methyl 20% WP @ 230 gha^-1(11.5 g a.i. ha^-1), T4= Pyrazosulfuran ethyl @ 125 g ha^-1(12.5 g a.i. ha^-1), T5= Weed free by hand weeding, and T6=Control (Unweeded). All treatments were laid out in a randomized complete block design with three replications. Twenty-five days of BRRI dhan49 for aman, and thirty-five days old seedlings of BRRI dhan28 for boro were transplanted at 20 x 20 cm spacing with 2 seedlings hill^-1. Fertilizers were applied as aman: N:P:K:S= 69:10:41:11 kg ha^-1 and boro; N:P:K:S= 120:19:60:24 kg ha^-1 (BRRI, 2013). All herbicides were sprayed at 1 to 2 leaf stage of weed (7 DAT in aman and 12DAT in boro) with the help of a knapsack sprayer. In weed free treatment, the plots were kept weed free up to 50 DAT by hand weeding. Metolachlor + bensulfuran methyl herbicide is innovative in Bangladesh and its phytotoxicity needs to be evaluated on rice crop. The phytotoxicity of the herbicide to rice plants was determined by visual observations (yellowing leaves, burring leaf tips, stunting growth, etc.). The degree of toxicity on rice plant was measured by the following scale used by IRRI (1965).

The rating of toxicity was done within 7 days after application of herbicides. It was observed three times at 3, 5 and 7 days after application of herbicide and the mean rate was calculated from 10 sample plants of a unit plot.

Data on weed density and dry weight were taken from each plot on 40 DAT. The weeds were identified species-wise. Dry weights of weeds were taken by drying them in electric oven at 600 C for 72 hours followed by weighing by digital balance. Relative weed density (RWD), relative weed biomass (RWB), The sum dominance ratio (SDR) and weed control efficiency (WCE) of different weed control treatments were calculated with the following formulas (Janiya and Moody, 1989; Rao ,1985). Data on panicle m^-2, grains panicle^-1, sterility and grain yield were collected. Yield attributes and yield data were analyzed with STAR 2.0.1 software for analysis of variance and graphical presentation.

Source of Information: Bangladesh Agron. J. 2018, 21(1): 61-70

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Results reveal that yield and yield attributes, and weed dynamics were greatly influenced by different weed management practices. Metolachlor + bensulfuran methyl 20% WP @ 230 g ha^-1 showed better weed control efficiency although it has slight phytotoxicity. On the other hand, Metolachlor + Bensulfuran methyl 20% WP @ 190 g ha^-1applied at 1 to 2 leaf stage would be more effective for controlling annual weeds in transplanted rice.

Knowledge Management: Journal