Evaluation of Metribuzin for Control of Rumex spp. in Wheat

The present study was carried out during Rabi season of 2017-18 at Department of Agronomy, Chaudhary Charan Singh Haryana Agricultural University, Hisar (Haryana) to evaluate the efficacy of metribuzin as a pre emergence intervention against Rumex spp. in wheat crop. It was applied at three doses (0.5X, X and 2.0X ) in pot experiment under Completely Randomised Design (CRD) replicated thrice with four populations of Rumex spp. named as HHH (HAU Hisar), UPH (Ujha, Panipat), JHH (Jind) and JJR (Jhajjar) collected from farmers fields of Haryana. One unsprayed control was also kept for each population for comparison. In observations, plant height, chlorophyll fluorescence, electrical conductivity (EC), percent control, fresh weight and dry weight were recorded. Metribuzin as pre-emergence intervention provided 100 per cent control of all biotypes. No emergence was found in pots sprayed with metribuzin even at half of the recommended dose of this herbicide. This is the key finding of this study because pre-emergence intervention with metribuzin could resolve the problem of resistant Rumex biotypes being faced by the farmers.


INTRODUCTION
Wheat (Triticum aestivum L.) is most important, widely cultivated and leading staple food crop of world with an area, production and productivity of 221.3 mha, 726.9 mt and 3290 kg/ha respectively (FAO STAT, 2016). In India, it occupies second rank after rice with 30.6 mha area with 99.8 mt production and 3220 kg/ha productivity (Anonymous, 2018). Haryana is the major wheat growing state of India with an area of about 2.53 mha, 11.7 mt production and 4.62 t/ha productivity (Anonymous, 2018a). Weed management is the key issue in the production package of wheat crop. Losses due to weeds in wheat productivity can be in range of 15-40% or even higher besides lowering down the quality of produce (Chopra et al., 2001). In some extreme cases, weeds can also cause complete failure of crop (Malik and Singh, 1995). Wheat is infested with diverse weed flora because it is grown in diverse agroclimatic conditions, under different cropping sequences, tillages and irrigation regimes (Chhokar et al., 2012).
Reduced tillage or no till wheat with higher moisture in ricewheat system favours the infestation of broad leaf weeds like Malwa parviflora and Rumex dentatus. At world level herbicide is a major tool of weed management in wheat due to its cost and time effectiveness. R. dentatus is a major broadleaf weed of Rabi season and is a serious problem of irrigated wheat particularly in rice-wheat cropping system in north-western Indo-Gangetic alluvial plains of India comprising of the state of Haryana, Punjab, and Western Uttar Pradesh (Sandhu & Dhaliwal, 2016). This weed is highly competitive and yield losses up to 55% have been reported (Heap, 2014).

Pot preparation: Soil of Agronomy
Research Farm area was used for filling the pots. The soil was free from seeds of Rumex spp. and did not have any herbicide exposure in the preceding two years. Plastic pots (6″ diameter) were filled with 2 kg material mixture of sand, field soil and vermi-compost.

Metribuzin dose-response studies
The pre-emergence application of metribuzin @ 105 g/ha, 210 g/ha and 420 g/ha provided 100 per cent control in all biotypes. The efficacy of metribuzin even at half of the dose is the significant finding of this study ( Table 3).
The metribuzin was applied as preemergence intervention and it provided 100 per cent control at all the three doses, hence no weed plant was available for recording plant height, Plant chlorophyll fluorescence, Electrical conductivity (EC) and Fresh and dry weight in any of the herbicide treatments.
These observations were recorded only in control treatments for different biotypes.
Plant height recorded in control treatment for the different biotypes at spraying, 2 and 4 WAT showed no significant variation (Table 1) (Table 2). No significant difference was observed among different biotypes with respect to electrical conductivity ( Table 4).

DISCUSSION
Rumex biotypes were found highly sensitive to pre-emergence application of metribuzin. It provided complete control in all biotypes. No emergence was found in pots treated with metribuzin. It is due to inhibition of photosystem II. These results are in conformity with findings of Malik et al. (2005) and Chhokar et al. (2006).

SUMMARY AND CONCLUSION
All the Rumex biotypes were found highly sensitive to pre-emergence application of metribuzin. This herbicide provided complete control in all biotypes even at half of the recommended dose of herbicide. This is the key finding of this study because preemergence intervention with metribuzin could resolve the problem of resistant Rumex biotypes being faced by the farmers without incurring extra cost as pre-emergence application of metribuzin also integrated for the control of grassy weeds. The dose callibration of metribuzin with respect to the complex weed flora in wheat crop may prove as highly efficacious and cost effective weed management practice.