Control of woodsorrel (Oxalis europaea Jord.) in wheat (Triticum aestivum L.) field by herbicides
Akbar Hossain1*, Jaime A. Teixeira da Silva2
1Wheat Research Center, Bangladesh Agricultural Research Institute, Dinajpur, Bangladesh; email: tanjimar2003@yahoo.com
2 Faculty of Agriculture and Graduate School of Agriculture, Kagawa University, Ikenobe, Miki-cho, 761-0795, Japan
*Corresponding author
Abstract
The control of woodsorrel (Oxalis europaea Jord.) in a research wheat field of the Wheat Research Center, Bangladesh, through the use of five herbicides (Affinity 50.75 WP at 1.25 kg ha-1; Hammer 24 EC at 100 ml ha-1; 2, 4-D Amine at 1200 ml ha-1; U 46 at 1400 ml ha-1; Lintur 70 WG at 100 g ha-1) was evaluated. A weedy check and hand weeding were also performed for comparison. All herbicides, which were applied post-emergence 30 days after sowing, could control woodsorrel 7 days after treat (DAT), except for 2, 4-D Amine. However, at 25 DAT, only Affinity could effectively (% weed mortality and % weed control efficiency (WCE) were 87.6 and 93.7%, respectively) control woodsorrel while 2, 4-D Amine was completely ineffective. The effectiveness of treatments could be ranked: Affinity caused the highest weed mortality at 7 and 25 DAT, followed by Hammer at 7 DAT and hand weeding at 25 DAT. When WCE was considered, Affinity also performed best followed by hand weeding, Hammer then Lintur. Considering both weed mortality and WCE, Affinity is recommended for controlling woodsorrel in wheat fields.
Key words: herbicides, weed control, woodsorrel, weed species, wheat.
Introduction
Weeds are unwanted plant species growing among domesticated crops. The concept of weeds as unwanted plants was born when humans started to grow plants deliberately for food and other purposes (Dangwal et al. 2010). Holm et al. (1979) estimated 250 weed species to be important for agricultural crops throughout the world. Hossain et al. (2008a, 2009b) and Islam et al. (2008) noticed that growth and yield-related components of maize were highly affected by weed infestation, finally reducing yield by 15%. Research findings from field and pot experiments revealed that growth (leaves, tillers, dry matter) and yield of rice were reduced due to weed infestation (especially Echinochloa crus-galli) and that this reduction was higher if rice was infested at an early stage (Hossain et al. 2006; 2008b). Donald and Easten (1995) observed that weeds limited wheat yield potential in arid regions because they increase evapotranspiration and compete with wheat plants for limited soil moisture, water and light, resulting in a wide range of reduction in grain yield: 7% (Shah et al. 2005), 52% (Khan et al. 2003), 92% (Tiwari and Parihar 1997), 25.35% (Dangwal et al. 2010). In serious cases, weed infestation would lead to complete crop failure (Abdul-Khaliq and Imran 2003).
In Bangladesh, wheat is the second major cereal crop after rice although the average yield of wheat is lower than that of other wheat-growing countries around the world (IndexMundi 2012). Several reasons can be explained for this low yield, one of the most important being weed infestation, reducing yield by 24.60 to 58.46% (Hossain et al. 2010a).
The major weeds affecting the wheat crop in Bangladesh are Oxalis europaea, Cynodon dactylon, Eleusine indica, Digitaria sanguinalis, Cyperus rotundus, Chenopodium album, Physalis heterophylla, Vicia hirsuta, Hydyotis brachypoda and Stellaria media (Hossain et al. 2010a, b, c). Among the wheat-infesting weed species, O. europaea was the second most important and comprised 18.18% of all weed species (Hossain et al. 2009a) (Fig. 1). From a field study, Hossain et al. (2010a, b, c) noted that wheat fields are normally infested by between 18 and 22 types of weed species belonging to 11-12 families. Among them, Oxalis spp. (Oxalidaceae) was the most important, accounting for 27-33% of the total.
Oxalis spp., widespread around the world, are also known as common yellow oxalis, yellow woodsorrel, sourgrass, oxalis, sheepsorrel, and toadsorrel. Although two sub-species of O. europaea, bushii (small) Wieg and rufa (small) Yong, are found globally (Halvorson 2003), in Bangladesh O. europaea Jord. is that most commonly observed in wheat fields (Hossain et al. 2010c) (Fig. 1 and Fig. 2).
Weed control is a basic requirement and a major component of production systems (Young et al. 1994; Hossain et al. 2009b). However, Bangladesh farmers are not interested in controlling weeds in wheat fields due to a labour crisis (during the same season, laborers are engage with cultivation of boro-rice and winter vegetables) during the wheat-growing period (WRC 2007). Therefore, the choice of herbicide, the proper application time and the proper dose are important considerations for maximizing returns (Bibil 2008). Consequently, the Wheat Research Center (WRC) of Bangladesh is trying to control weeds in wheat fields and some of the studies that emerged from those efforts are presented in Table 1. However, to date, no study exists on the specifical control of woodsorrel through the use of herbicides in Bangladesh. Thus, the present study aimed to assess the effectiveness of five post-emergence herbicides in controlling woodsorrel in a wheat field.
Materials and Methods
The experiment was carried out during the 2008-09 wheat season in a research field of the WRC of the Bangladesh Agricultural Research Institute, Dinajpur, Bangladesh. The area is under the Old Himalayan Piedmont Plain designated as Agro Ecological Zone-1 (FAO/UNDP 1988), at 25°38´ N, 88°41´ E and 38.20 m above sea level. Pre-seeding soil was sandy loam with pH 5.6 (WRC 2007).
The experiment was laid out in a randomized complete block design with 7 treatments each replicated 3 times. The treatments were weedy check (control), Affinity 50.75 WP, Hammer 24 EC, 2, 4-D Amine (2,4-D-dichlorophenoxyacetic acid), U 46, Lintur 70 WG and hand weeding. These herbicides were used as experimental treatments since these are currently marketed herbicides approved for use by the Bangladesh government (DAE 2011). All the herbicides were applied as post emergence at 30 days after sowing (DAS), when the crop was in the 5-6 leaf stage. Hand weeding was also performed at 30 DAS. Herbicides were applied as an aqueous suspension with a knapsack sprayer. The trade name and chemical composition of each herbicide and their rates of application are outlined in Table 2.
Unit plot size was 3 m x 4 m. Seeds of a popular wheat variety ‘Prodip’ were treated with Provax-200 WP (3 g kg-1 wheat seed), an effective seed-treating fungicide consisting of Carboxin and Thiram. ‘Prodip’ was selected as the experimental material due to its popularity in the northern part of Bangladesh (Pandit et al. 2011) and because it showed the highest competitive ability against weeds (Hossain et al. 2010b). Sowing was performed on 4th December 2008 in lines with 20-cm spacing between rows and seeded at a rate of 140 kg ha-1. Recommended fertilizer doses 100-27-40-20-1 kg ha-1 of N-P-K-S-B respectively, were applied. The crop was irrigated at the crown root initiation, booting and grain-filling stages. Intercultural operations were done properly according to treatments.
Observations on weed density were made using a quadrat method as described by Pound and Clements (1998).
Total number of weeds
Density (no. m-2) = -------------------------------
Total surveyed area (m2)
Data on O. europaea was recorded immediately before treatment (IBT) at 30 DAS, at 7 days after treat (DAT) (i.e., 37 DAS) and at 25 DAT (i.e., 55 DAS). Weeds inside the quadrat measuring 1 m x 1 m were identified and counted. The weeds which were carefully uprooted were washed thoroughly in clean water and dried first in the sun for two days and thereafter in an electric oven for 48 h at 80°C. The weight of the dried sample was taken and the average data was expressed as weed dry weight (g m-2). Data on % weed control efficiency (WCE) (Kabir et al. 2008) and % mortality (Hussain et al. 2011) were calculated according to the following formulae:
Number of weeds before spray – number of weeds after spray
Mortality (%) =-------------------------------------------------------------------------------- x100
Number of weeds before spray
Dry weight in control plot – dry weight in spray plot
WCE (%) = -------------------------------------------------------------------------x100
Dry weight in control plot
Data was compiled and subjected to statistical analysis. Analysis of variance and a mean separation test were done according to Gomez and Gomez (1984).
Results and Discussion
Density (no. m-2) and % mortality of woodsorrel
The number of woodsorrel in all treatments before spray was not significantly affected (Fig. 3). Data was recorded at 7 and 25 DAT for all the herbicides relative to the control except for 2, 4-D Amine, which could not control woodsorrel at all. Among the herbicides, the highest occurrence of woodsorrel was also observed in the weedy check, followed by 2, 4-D Amine, U46 and Hammer treatments and the lowest amount was recorded in the Affinity-treated plot followed by Hand weeding (Fig. 3). Similar finding related to broadleaf and narrow leaf control by these herbicides was observed by Hossain et al. (2009a, 2010a). Considering weed mortality (%) at 7 DAT by herbicides and hand weeding relative to the weedy check, Affinity caused the highest weed mortality (100%), followed by Hammer (88.6%), hand weeding (50.3%), Lintur (48.9%), 2, 4-D Amine (34.58 %) and U 46 (8.3%) (Fig. 3). On the other hand, data recorded at 25 DAT in the herbicide-treated plots indicated that only Affinity could control woodsorrel (87.6%) up to 25 DAT. However, the hand-weeded plot (93.4%) had a higher value than Affinity, indicating the effectiveness of hand weeding (despite the time and labor costs), while other herbicides could not control woodsorrel up to 25 DAT (Fig. 4). Hossain et al. (2010a) stated that when mortality of both narrow and broad-leaved weeds is considered, Affinity (86.31%) was found to be best followed by hand weeding (73.67%), Lintur (72.78%), Hammer (57.02%), U46 (47.98%) and 2, 4-D Amine (28.93%). Thus, Affinity was considered to be the most effective herbicide since it could control all types of weeds.
Dry biomass (g) and % WCE of woodsorrel
The dry biomass of woodsorrel varied among different weed control treatments (Fig. 5). Compared to the weedy check, a higher dry biomass was observed in the 2, 4-D Amine-sprayed plot due to poor control of woodsorrel, followed by U 46, Lintur, hand weeding and Hammer at 7 DAT. By considering %WCE at 7 DAT relative to immediately before spray (IBT) plots, Affinity (100%) produced the highest biomass, followed by Hammer (96.4%), Lintur (71.3%) and U46 (59.8%) (Fig. 5). At 25 DAT, 2, 4-D Amine and U 46 did not control weed (% WCE were -29.8% and -15.4%). The highest % WCE was observed for Affinity (93.7%), followed by hand weeding (93.4%), Hammer (63.9%) and Lintur (42.2%) at 25 DAT (Fig. 6). Hossain et al. (2010a) also evaluated these herbicides in same agro-ecological conditions and noted that % mortality and WCE of Affinity was also the highest, followed by hand weeding while the performance of 2, 4-D was worst.
Conclusion
All five herbicides tested, except for 2, 4-D Amine, could control woodsorrel at 7 DAT. However, at 25 DAT, only Affinity could control woodsorrel while 2, 4-D Amine was completely ineffective. Affinity resulted in the highest weed mortality at 7 and 25 DAT. When WCE is considered, Affinity also performed better than hand weeding, Hammer and Lintur, and when taking weed mortality and WCE into consideration, Affinity is recommended for the control of woodsorrel in wheat fields.
Acknowledgement
We are most grateful to the staff of the Wheat Research Center, Bangladesh for maintaining the experiment. Especially, the Director of the Wheat Research Center and the Director General of the Bangladesh Agricultural Research Institute (BARI) are also gratefully acknowledged for financial support to complete this experiment.
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