Weeds are the most destructive agricultural pests. Most of the weeds drive their nourishment from rapid development and manifested through quick root and shoot development than crop. For the competitive abilities weeds form a serious negative effect in crop production and responsible for marked losses in crop yield (Mamun et al., 1993). Karim et al. (1998) reported that the probable yield loss due to unrestricted weed competition was 28.28% in broad cast aman rice.
Weed infestation is a major problem in wet-seeded rice culture due to alternate wetting and drying as is practiced during the initial seedling growth. The similarities in age of the weed and rice seedling and morphological features of young grassy rice seedlings make hand weeding more difficult in wet-seeded rice. Mechanical weeding would not be possible unless sowing is done in rows. Obviously the use of herbicides is one of the effective means of controlling of weeds in aman rice under wet-seeded culture.
The farmers of Bangladesh are not familiar with the effectiveness of herbicides in controlling weed. On the other hand, very little work has been done. In view of the current availability of herbicide in the market and their effectiveness against grasses, sedges and broad leaved weeds, Ronstar 25EC, Setoff 20WG and Golteer 5G were selected to evaluate the effectiveness in controlling the weeds of aman rice grown under wet-seeded culture.
Materials and Methods
The study was conducted at the Agronomy Field Laboratory, Department of Agronomy, Bangladesh Agricultural University, Mymensingh during July to December 1998. The popular transplanted aman rice variety BR11 (Mukta) was selected for wet- seeded culture experimentation. It is non-lodging taking 140-145 days to complete its life cycle and can be successfully grown in aman season. The yield ranges between 5.5 to 6.5 tons ha-1 (Anonymous, 1991).
The single factor experiment was laid out in a randomized complete block design (RCBD). Thus, the treatment combinations was thirty and unit plot size was 4.0 x 2.5m2. The spacing between plot to plot was 1.0 and block to block were 1.5 m. The treatments were randomly assigned in the unit plots of each block.
The common names of Ronstar 25EC, Set off 20WG and Golteer 5G are- Oxadiazon,
Cinosulfuron and Butachlor.
There were ten treatments in this study namely.
||Ronstar 25 EC @ 1.0 l ha-1,
|| Ronstar 25 EC @ 2.0 l ha-1,
||Ronstar 25 EC @ 3.0 l ha-1,
||Set off 20 WG @ 50 g ha-1 ,
||Set off 20 WG @ 100 g ha-1,
||Set off 20 WG @ 200 g ha-1,
||Golter 5G @ 12.35 kg ha-1,
||Golter 5G @ 24.7 kg ha-1 ,
||Golter 5G @ 49.4 kg ha-1.
In control, no weeding as well as no weedicide were used. All the three weedicide
were used as pre-emergence application. Certified seeds of BR11 was treated
with vitavex-200 @ 2.5 g kg-1 of seeds (Anonymous, 1979). Seeds were
sown @ 80 kg ha-1.
For land preparation the land was irrigated and puddled thoroughly by ploughing three times with the country plough and the weeds and stubbles were thoroughly cleaned from the prepared field.
Fertilizers were applied to the plots @ 60, 8, 30 and 4 kg ha-1 as N, P, K and S on the basis of Fertilizer Recommendation Guide (Anonymous, 1997) through urea, TSP, MP and gypsum, respectively. Seeds were evenly broadcasted on unit plot when about 80% of the seeds were sprouted, using conventional method. Irrigation was done as and when necessary.
A quadrat of 1 x 1 m2 was randomly placed on each plot and all the weeds (species -wise) in the quadrat was counted on 21st October, 1998. Then the average number of weeds (species-wise) per plot was computed from the results obtained in sampling. Thus, the computed on weed number were used to determine the following parameters.
The following attributes were computed from the computed data
||Population density (PD) of weed=
Total number of weeds of all species m-2
||Dry weight of weed- the weeds in each quadrate were uprooted, washed and
dried in the sun and then in an electrical oven for 24 hours at a constant
temperature of 700C. After drying, weight each species was taken
and converted it for 10 m2.
Weed control efficiency on the basis of dry weight was calculated using the
||weed control efficiency
||Dry weight of weeds in weedy check
||Dry weight of weeds in mechanical and chemical treatments
The extent of weed control by different weed control treatments and susceptibility
of different weed species were graded on the basis of weed control efficiency
by the following scales as suggested by Mian and Gaffer (1968)
Percent of weed control: The percent of aquatic weed control by each
of the weed control method were calculated by the following formula:
The data recorded were compiled and tabulated in proper form and subjected
to statistical analysis. The mean differences among the treatments were adjusted
by Duncans new multiple range test (Gomez and Gomez, 1984).
Results and Discussion
The results showed that three doses of Setoff 20WG and Golter 5G performed more or less similar weed control efficiency. However, there was no significant difference in weed control efficiency between Setoff 20WG and Golter 5G (Table 1).
The best efficiency in controlling Fimbristylis miliaceae (81.248%) was observed with Golteer 5G and Setoff 20WG at 49.4 kg ha-1 and 200 g ha-1, respectively (Table 1).This findings were also reported by Burhan et al. (1989). Lee et al. (1989) to evaluate the use of Tridiphane and bensulfuron-methyl at 30 g ha-1 against Monochoria, arrowhead and small flower umbrella plant, moderate activity against bulrush and poor activity against barnyard grass. Bensulfuron-methyl (Setoff 20WG group) has shown a high level of activity against broad-leaved weeds and sedges in sedges in paddy in Spain and Portugal. Bensulfuron-methyl was well tolerated by the local rice cultivars (Muntan, 1989).
Singh and Pillai (1993) to evaluate the epicacy of selected herbicides for direct sown rice under puddled conditions with Butachlor at 1.5 kg ha-1, Benthiocarb at 1.5 kg and Anilofos at 4 kg ha-1, at 3, 6, 9 and 12 DAS that in comparison with the hand weed and non weeded treatment. They found that weed control in the Butachlor, Thiobencarb, Anilofos and the hand weeded control treatments was 69.3, 67.6, 71.2 and 91.6%, respectively. Vijayaraghavan et al. (1998) reported that Butachlor +one HW provided the best weed control (78%). Mabbayad and Moody (1985) found the dry weight of weeds, especially Monochoria vaginalis, Echinochloa glabrescens and Echinochloa colonum 45 days after sowing was lowest with Butachlor applied at the rate of 0.6 kg ha-1 3 days before sowing.
The herbicidal treatments (T1 to T9 ) showed that their
effectiveness in controlling weeds varied from poor to good and also showed
the susceptibility grades from poor to high. The best performance (82.8% destruction)
was observed in T1 and the second highest weed killing epicacy (82.35%)
was also demonstrated by T1.
|| Infesting species of weed in wet-seeded rice and their degree
of susceptibility to control by different treatments
||Effect of Ronstar 25EC, Setoff 20WG and Golter 5G on weeds
in wet seeded rice cv.BR11
|In a coloum the values having common letter(s) do not differ
significantly Figures in the paranthses indicate per cent decrease of the
concerned parameters compared to the values in the control treatment.
Patanker (1992) in the trial in up land rice during kharif season found that
Ronstar 25EC at 1.0 kg a.i./ha followed by 2,4- D at 1.5 kg/ha +5% jaggery (course
brown sugar) applied 30 days after sowing effectively controlled annual broad-leaved
weeds and grasses.
The efficiency of different treatments to destroy different species of weeds varied among themselves and also with the weed species. From the results, it is clear that the performance of three herbicidal treatments in controlling weeds varied from good to poor (Table 1). Out of three herbicides, three levels of Ronstar 25EC resulted better performance than the doses of Setoff 20WG and Golteer 5G. Further, out of the three levels of Ronstar 25EC of 1.01l/ha yielded the highest effiency. The results demonstrated that three major species (Monochoria vaginalis Panicum ripens and Fimbristylis diphylla) were fair to good control and moderate to highly susceptible to Ronstar 25EC and Setoff 20WG; while rest of the weeds species were moderate to highly susceptible and controlled by different treatments of Ronstar 25EC, Setoff 20WG and Golteer 5G.
Weed population/m2 varied significantly at 1% level of significance. The highest number of weed population (56.33) was observed in control (T0); while the lowest (20.67) was found in T1 and T2 treatment which decreased 19.64% of weed population in compared to control (T0). However, there was no significant difference between T1 and T2 in respect of weed destruction. On the other hand, Golter 5G @ 12.35 and 24.7 kg ha-1 (T7 and T8) suppressed the higher percentage of weed population (10.76%) than control (T0). The second highest weed controlling epicacy was found in T5 and T6 which resulted in 13.72% destruction in comparison with T0 (Table 2).
Weed dry weight was significantly affected due to application of different treatments at 1% level of significance. In control (T0) the maximum dry weight of weed was maximum (11.75 g m-2 ) and was minimum (3.67 g m-2) were observed in T0 and T3 treatments, respectively. Weed dry weight was also found to be significant (T1 to T9). The highest weed dry weight reduction (69.36%) was observed in T3 in comparison with control (T0). On the other hand, the lowest weed dry weight decrease (33.02%) was found in T1 (Table 2).
Intensity of weed infestation did not exert any significant variation. The highest (0.28%) intensity of weed infestation was observed in control (T0); while the lowest (0.07%) intensity of weed infestation was found in T1 which was almost similar to T6. Out of three herbicides in Setoff 20 WG treatments showed average minimum weed infestation than in Ronstar 25EC and Golter 5G. Ronstar 25EC @ 1.0 l/ha decreased the highest level of weed intensity (75%)than any other treatments involved in the experiment (Table 2).
Different treatments of weed control influenced population density, intensity of weed infestation and weed dry weight in various ways. Ronstar 25EC at 1.0l ha-1 showed the best weed control performance (64.21%) which was identical with that of Ronstar 25EC at 2.0 l ha-1.