Clodinafop, Cross resistance, Farmer field, Sulfosulfuron
Little seed canary grass (Phalaris minor Retz.) is the dominant grass weed of wheat especially in rice-wheat cropping system in the North-Western Indo-Gangetic Plains of India. It developed resistance to isoproturon herbicide in early 1990’s. Alternate herbicides, viz. clodinafop, sulfosulfuron and fenoxaprop were recommended for its control and were widely adopted by the farmers. Complaints of poor efficacy of these alternate herbicides started appearing at farmers’ field, after decades of their use. Performance of these alternate herbicides was assessed, to study the occurrence of cross resistance in P. minor, through farmers’ field survey. The survey was conducted in 2011 at 73 farmers’ field in six districts viz. Patiala, Fatehgarh Sahib, Ludhiana, Moga, Jalandhar and Ropar in Punjab. The survey indicated that clodinafop and sulfosulfuron are widely used by the farmers. The farmers used to apply field rates of these herbicides till 2008-09 and were getting effective control of P. minor (>85%). During 2009-10, clodinafop started showing signs of reduced efficacy and >30% farmers used 1.5 times of field dose and control was still poor (<65%); few farmers (<10%) used 2 times the field dose with little success. In 2010-11, the farmers (<50%) used 2 times and <30% used 3 times or higher dose of clodinafop alone/tank mix of clodinafop + sulfosulfuron/both herbicides in sequence and control was still poor (0- <60%); re-growth recorded in Patiala, Fatehgarh Sahib, Ludhiana and Moga districts. Sulfosulfuron efficacy also showed declining trend (<60%) during 2010-11. Reduced efficacy of sulfosulfuron was more prevalent in fields having history of continuous use of sulfosulfuron but poor efficacy of clodinafop was even recorded in fields having continuous use of sulfosulfuron. The spray methodology adopted by the farmers was better than they were using in the previous years, hence cannot be related to the reduced herbicide efficacy. The survey results pointed towards the development of cross resistance in P. minor to clodinafop and indicated that sulfosulfuron was likely to meet the same fate in the near future. Proper and regular monitoring of all the existing herbicides is desirable before the situation comes out of control at farmers’ field.