Effect of repeated spraying and efficacy of some herbicides on weed control and yield of alfalfa (Medicago sativa)

To study the effect of herbicides in alfalfa weed control in South Kerman, an experiment was conducted in a randomized complete blocks design with three replications in the Agricultural Research and Education Center, Jiroft, Iran during 2013-2014. Treatments included application of once and twice 5 L/ha EPTC herbicide, 750 g/ha metribuzin, 3 and 3.5 L/ha 2, 4-DB, 3 L/ha bentazon, 0.5 L/ha imazethapyr plus 200 ml/ha Citogate and 1 L/ha imazethapyr as post- emergence, and weed infested as control. Results showed that herbicide applications had significant effects on density and dry weight of weeds and alfalfa dry weight. Herbicide applications significantly decreased density and dry weight of weeds. Once and twice spray application of imazethapyr (1 and 0.5 L/ha) had a good efficiency in weed control. Also, once and twice spray application of 1 L/ha imazethapyr reduced weed dry weights 78 and 77% in the first, 78 and 77% in the second, and 86 and 82% in the third alfalfa harvest . Imazethapyr and EPTC herbicides had no alfalfa leaf injury and increased dry weight of alfalfa during three harvests. Although, 2, 4-DB herbicide showed good weed control, but these treatments had leaf injury in the first alfalfa harvest. Twice and once spray application of imazethapyr (1 L/ha) resulted in the highestalfalfa yield. This treatment increased alfalfa biomass 32 and 28% in the first, 30 and 28% in the second and 33 and 30% in the third harvests. Therefore, once spray application of 1 L/ha imazethapyr is recommended because of its efficiency in weed control and yield increasing.