Turmeric (Curcuma longa L.), a herbaceous perennial plant, belonging to the family Zinziberaceae under the order Scitaminae is one of the most valuable spices all over the world. It is also called as “Indian saffron”. Turmeric (Curcuma longa L.) is one of the second most important spice crops after chilli. India accounts for 78 per cent in world production and 60 per cent in world export share (Angles et al., 2011). Among the several spices, turmeric ranks second in foreign exchange earnings, being next only to chilli. The turmeric is native of South-East Asia, cultivated extensively in India, Myanmar, Nigeria, Pakistan, Sri Lanka, Indonesia, Bangladesh, Taiwan and China. The major states in India which grow turmeric are Andhra Pradesh, Orissa, Tamil Nadu, Assam, Maharashtra and Karnataka. Andhra Pradesh alone occupies 35 per cent of area and 47 per cent of production. In Tamil Nadu, it is grown in the districts of Erode, Coimbatore, Dharmapuri and Salem. Erode district alone contributes more than 10 per cent of the national production (Kandiannan and Chandaragiri, 2004). Nearly six per cent of the total area under spices and condiments is being occupied by turmeric in India. The area under turmeric in the country is around 218.65 million hectares and the production is 1166.84 million tonnes. In Tamil Nadu, turmeric is cultivated in an area of 60.23 lakh hectares with an annual production of 326.14 million tonnes. The productivity of the crop is 5.42 t·ha^-1 (Anon, 2013). Indian turmeric is regarded as the best in the world market because of its high curcumin content. During the periods between April 2011 to January 2012, the turmeric export from India was 67, 000 tonnes valued at 6438 million and contributed to 12.8 per cent of total spice export (Satya Sundaram, 2012).  Though, India leads in production of turmeric with 78 per cent of global production, its average productivity is quite low, mainly due to the competition offered by weeds. Weeds are the most severe and widespread biological constraint to crop production and cause invisible damage till the crop is harvested. Heavy infestation of weeds comprising of grasses, sedges and broadleaved weeds poses a big challenge for turmeric production in India.

Verma and Singh (1997) observed that plant height, leaves plant^-1, fresh and dry weight of plant were significantly higher under weed free condition in onion. In onion, Dandge and Satao (1999) found that weed free treatment recorded maximum plant height and number of leaves plant^-1. Vora and Mehta (1999) indicated that maximum number of leaves plant^-1 and neck thickness was recorded under weed free check in garlic. In turmeric, the maximum number of plant height, number of leaves plant-1, number of tillers plant^-1, dry matter production, leaf area and LAI were observed in weed free check plots due to reduction in weed population as noticed by Mannikeri (2006) and Babu (2008). According to Kaur et al. (2008), unweeded control recorded lesser leaf area index than all other herbicide treatments in turmeric. Pre-emergence application of pendimethalin 1.0 kg·ha^-1 recorded higher LAI, LAD, CGR and NAR in turmeric (Channappagoudar et al., 2013). Herbicides are the key products in sustaining large scale agricultural production but in order to minimize agro-environmental concerns regarding their use, continued assessment of their behaviour under different management practices is required. Chemical weed control is a better supplement to conventional method and forms an integral part of the modern crop production. It is quick, more effective, time and labour saving method than others (Tahir et al., 2009). Presently a number of herbicides like pendimethalin, metribuzin and oxyfluorfen etc. are commercially available for weed control in turmeric. Being a long duration crop, pre-emergence herbicides alone will not provide a sustainable and effective weed management. Based on the above constraints, we are taken the objective of study the efficacy of pre and post emergence herbicides in IWM on weed control and morphological growth of turmeric.

1 Materials and Methods
1.1 Materials
Field experiments were carried out during kharif 2012 at Agricultural Research Station, Bhavanisagar of Tamil Nadu Agricultural University, to evaluate the integrated weed management with pre and post emergence herbicides in turmeric. The details of the experiment, the materials used and the methods employed during the course of investigation are presented in this chapter.

Soil characteristics
Composite soil sample was collected at random prior to the experiment, pooled and analysed for physico- chemical characteristics. The soil of the experimental field was red sandy loam in texture belonging to Typic Haplustalf. The nutrient status of the field was low in available nitrogen, medium in available phosphorus and high in available potassium. The detailed physico-chemical properties of the experimental field are furnished in Table 1.

Table 1 Physico-chemical characteristics of the experimental fields

Season
The experiments were conducted during kharif (May-June) season, 2012.

Crop and variety
Turmeric variety BSR 2 with a duration of 240-245 days was selected for this study and the seeds were procured from ARS, Bhavanisagar. The characteristic features of the variety BSR 2 are presented in Table 2.

Table 2 Varietal characteristics of turmeric BSR 2

1.2 Experimental Methods
Design and layout
The experiments were laid out in Randomized block design comprised of fifteen treatments. The treatments were replicated thrice. The lay out plan of the experimental field during 2012. The experimental details are furnished below (Table 3; Table 4).

Table 3 Potato cultivars used in the trial

 

Table 4 Potato cultivars used in the trial

2 Result and Discussion
Turmeric is a long duration crop. Delayed emergence, slow initial growth of the crop and ample land space available due to wider spacing permit more sunlight to reach the soil resulting in conducive environment for rapid weed growth and enormous damage to crop yield. The magnitude of yield loss varies from 30 to 75 per cent, depending upon the growth and persistence of weed density in the standing turmeric crop (Krishnamurthy and Ayyaswamy, 2000). The traditional weeding operation is arduous, time consuming, back breaking and may not be undertaken at appropriate time due to non-availability of labours during peak period. So, it is not possible to control the weeds timely with the traditional methods like hand weeding. Chemical weed control is an alternative practice for the control of weeds. In view of the importance of chemical weed control in turmeric, field experiments were carried out during kharif 2012 at Agricultural Research Station, Bhavanisagar of Tamil Nadu Agricultural University, to evaluate the integrated weed management with pre and post emergence herbicides in turmeric. The results of the experimentation are discussed below.
 
2.1 Plant height
Plant height was significantly influenced by different weed control treatments. During kharif 2012, at 60 DAP, pre-emergence application of metribuzin 0.7 kg·ha^-1 + HW on 45 and 75 DAP (T1) recorded significantly taller (44.7 cm) plants than other weed control treatments. However, the plant height of pre-emergence application of metribuzin 0.7 kg ·ha^-1 + HW on 45 and 75 DAP (T1) was comparable with that of PE pendimethalin 1.0 kg·ha^-1 + HW on 45 and 75 DAP (42.2 cm), hand weeding at 25, 45 and 75 DAP (41.7 cm) and PE oxyfluorfen 0.30 kg·ha^-1 + HW on 45 and 75 DAP (40.2 cm). Unweeded check (T15) recorded significantly shorter plants (29.1 cm) and it was at par with POE glyphosate 1.54 kg·ha^-1 on 25 DAP + HW on 45 and 75 DAP (31.5 cm), PE atrazine 0.75 kg·ha^-1 + POE fenoxaprop 67 g·ha^-1 + metsulfuron 4 g·ha^-1 (Tank mix) on 45 DAP (32.2 cm), PE pendimethalin 1.0 kg·ha^-1 + POE fenoxaprop 67 g·ha^-1 + metsulfuron 4 g·ha^-1 (Tank mix) on 45 DAP (32.3 cm), PE atrazine 0.75 kg·ha^-1 + straw mulch 10 t·ha^-1 on 10 DAP + HW on 75 DAP (33.9 cm), PE metribuzin 0.7 kg·ha^-1 + POE fenoxaprop 67 g·ha^-1 + metsulfuron 4 g·ha^-1 (Tank mix) on 45 DAP (34.4 cm) and PE pendimethalin 1.0 kg·ha^-1 + straw mulch 10 t·ha^-1  on 10 DAP + HW on 75 DAP (34.6 cm). The same trend was observed in 120, 180 and 240 DAP.

Growth attributes like plant height, dry matter production, number of tillers plant^-1 and leaf area development are the reflective processes of effective utilization of resources in a better crop production environment. Conducive crop growth environment with minimum stresses due to biotic factors like lesser weed competition reflects further on better yield attributes of crops. Dramatic variations in growth and yield attributes of turmeric was noticed due to different weed control methods primarily associated with change in weed flora composition with varying weed density and weed dry weight. In turmeric during both the years of study, pre-emergence application of metribuzin 0.7 kg·ha^-1 + HW on 45 and 75 DAP recorded comparatively taller plants than un-weeded check (Table 5), which may be attributed to better weed control with favourable soil environment that might have resulted in reduced crop-weed competition for the growth factors such as light, space and nutrients which in turn helped in efficient photosynthetic activity recording taller plants. Decreasing weed density results in increased plant growth was supported by Hashim et al. (2003) and Jan et al. (2004). Among the treatments imposed, PE atrazine 0.75 kg·ha^-1 + POE fenoxaprop at 67 g·ha^-1 + metsulfuron at 4 g·ha^-1 (Tank mix) on 45 DAP (T8)  and unweeded check (T15) showed significant reduction in plant height at all the growth stages of the crop. This was attributed to suppressing effect of uncontrolled weeds by these treatments on crop plants. Similar findings have been reported by Chander et al. (1997). From the experimental results, it is evident that high competition of weeds reduced the input availability to plants, thus reduced the plant height to a greater extent. PE pendimethalin 1.0 kg·ha^-1 + HW on 45 and 75 DAP (T4) and hand weeding on 25, 45 and 75 DAP (T14) resulted in better growth of turmeric recording comparatively taller plants than unweeded control. Efficacy of pre-emergence herbicide or manual weeding in controlling the weeds at critical crop-weed competition of up to150 DAP in turmeric might be the reason for better growth of turmeric.

Table 5 Potato cultivars used in the trial

2.2 Dry Matter Production
Dry matter production was significantly influenced by different weed control treatments and is presented in Table 6. There was a steady increase in DMP from 60 DAP to 240 DAP.
 

Table 6 Potato cultivars used in the trial

During kharif 2012, at 60 DAP, the dry matter production was lucidly higher (2 387 kg·ha^-1) in pre-emergence application of metribuzin 0.7 kg ·ha^-1 + HW on 45 and 75 DAP which was comparable with PE pendimethalin 1.0 kg·ha^-1 + HW on 45 and 75 DAP (2271 kg·ha^-1) and hand weeding at 25, 45 and 75 DAP (2238 kg·ha^-1). Unweeded check (T15) resulted in significantly lower DMP (1 110 kg·ha^-1) which was comparable with PE pendimethalin 1.0 kg·ha^-1 + POE fenoxaprop 67 g·ha^-1 + metsulfuron 4 g·ha^-1 (Tank mix) on 45 DAP (1 207 kg·ha^-1) and PE atrazine 0.75 kg·ha^-1 + POE fenoxaprop 67 g·ha^-1 + metsulfuron 4 g·ha^-1 (Tank mix) on 45 DAP (1 242 kg·ha^-1). At 120 DAP, the lower dry matter production was recorded with unweeded check (1 868 kg·ha^-1), which was comparable with PE atrazine 0.75 kg·ha^-1 + POE fenoxaprop 67 g·ha^-1 + metsulfuron 4 g·ha^-1 (Tank mix) on 45 DAP (2119 kg·ha^-1). Pre-emergence application of metribuzin 0.7 kg·ha^-1 + HW on 45 and 75 DAP (T1) registered distinctly higher (5167 kg·ha^-1) DMP, but it was comparable with pre-emergence application of pendimethalin 1.0 kg·ha^-1 + HW on 45 and 75 DAP (4906 kg·ha^-1). At 180 and 240 DAP, the same trend was observed. The dry matter production was drastically reduced in PE atrazine 0.75 kg·ha^-1 + POE fenoxaprop 67 g·ha^-1 + metsulfuron 4 g·ha^-1 (Tank mix) on 45 DAP (T8), PE pendimethalin 1.0 kg·ha^-1 + POE fenoxaprop 67 g·ha^-1 + metsulfuron  4 g·ha^-1 (Tank mix) on 45 DAP (T5) and PE metribuzin 0.7 kg·ha^-1 + POE fenoxaprop 67 g·ha^-1 + metsulfuron 4 g·ha^-1 (Tank mix) on 45 DAP (T2) besides unweeded check at 180 and 240 DAP. Pre-emergence application of metribuzin 0.7 kg·ha^-1 + HW on 45 and 75 DAP resulted in conspicuously higher DMP at 180 and 240 DAP (9561 and 11518 kg·ha^-1, respectively) and it was at par with PE pendimethalin 1.0 kg·ha^-1 + HW on 45 and 75 DAP (T4) and hand weeding at 25, 45 and 75 DAP (T14). More plant dry matter production with pre-emergence application of metribuzin 0.7 kg·ha^-1 + HW on 45 and 75 DAP might be due to lesser weed competition, as weeds might have been killed from their germination phase and keeping weeds at lower density. Superiority of metribuzin in controlling board spectrum of weeds reduced the weed density and thus weed dry weight resulted in higher plant dry matter was earlier reported by Suryanarayana Reddy (1993). In general reduction in nutrient removal by weeds through suitable weed management practices enhanced the nutrient uptake and dry matter production of the crops (Kaur et al., 2008).

2.3 Number of tillers
The treat mental effects on the number of tillers plant^-1 observed at various stages are presented in Table 7. In general, the tiller production continued up to 180 DAP. The formation of tiller was highly influenced by different weed management treatments. During kharif 2012, in all the stages of observation, pre-emergence application of metribuzin 0.7 kg·ha^-1 + HW on 45 and 75 DAP recorded (T1) significantly higher number of tillers plant^-1. This was comparable with PE pendimethalin 1.0 kg·ha^-1 + HW on 45 and 75 DAP (T4) and hand weeding at 25, 45 and 75 DAP (T14). The number of tillers plant-1 was moderate in PE oxyfluorfen 0.30 kg·ha^-1 + HW on 45 and 75 DAP (T10) and PE metribuzin 0.7 kg·ha^-1 + straw mulch 10 t·ha^-1 on 10 DAP + HW on 75 DAP (T3). Pre- emergence application of metribuzin 0.7 kg·ha^-1 + HW on 45 and 75 DAP recorded significantly higher number of tillers plant^-1 than other treatments at all the stages in both the years (Table 5). This might be due to very effective suppression of weed flora by the herbicide at early stage of the crop and subsequent removal of late emerging weeds by hand weeding at 45 and 75 DAP and eventually resulted in higher number of tillers in turmeric. This finding is in conformity with the results of Channappagoudar et al. (2007).
 

Table 7 Potato cultivars used in the trial

Acknowledgement
The research have been supported and facilitated by Tamil Nadu Agriculture University. Tamil Nadu. India. I extend my sincere thanks to Dr. N. K. Prabakaran, Professor (Agronomy) for given a valuable guidance during my Ph.D research and I special thanks to my Ph.D members, Professor and Head (Department of Agronomy) and Dr. K. Velayudham, Director of Crop Management, TNAU for given a guidelines to correct direction during my research.

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