Herbicides Efficacy in Control of Broad-Leaved Weeds in New Seeded and Established Alfalfa (Medicago sativa L.) in Alborz Province

This experiment was conducted during 2015-2016 in Karaj to evaluate the performance of some herbicides in view of broad leaf weeds control in new- seeded and established alfalfa. The efficacy of 2,4-DB (Butress( in weed control of alfalfa was compared with commonly used herbicides in alfalfa.
The experiment was performed in randomized complete-block design with 4 replications and 12 treatments. In new-seeded alfalfa, the treatments were included EPTC (Eradican) 5 L/ha, Metribuzine (Sencor) 750 g/ha, 2,4-DB (Butress) 3 and 3.5 L/ha, Bentazon (Bazagran) 3 L/ha, Imazethapyr (Persuite) 0.5 and 1 L/ha, and without herbicide control treatment. In established alfalfa, the herbicide treatments was the same, but metribuzine and EPTC were not used.
In new-seeded alfalfa, the best treatments for density decrease of Sisymbrium irio, Descurania sophia and Malcolmia africana were Metribuzine 750 g/ha, Bentazone 3 L/ha, and Imazethapyr 1 L/ha. The best treatments for biomass decrease of Sisymbrium irio were Bentazon (Bazagran) 3 L/ha and Imazethapyr (Persuite) 0.5 and 1 L/h, The best treatments for biomass decrease of Descurania sophia were Bentazon (Bazagran) 3 L/ha, Imazethapyr (Persuite) 0.5 and 1 L/h, and Metribuzine (Sencor) 750 g/h. The best treatments for biomass decrease of Malcolmia africana were Bentazon (Bazagran) 3 L/ha, Imazethapyr (Persuite) 0.5 and 1 L/h, Metribuzine (Sencor) 750 g/h, and 2,4-DB (Butress) 3 and 3.5 L/ha. The best treatments for increasing yield in new-seeded alfalfa during first harvest was Imazethapyr 1 L/ha, during second harvest were Imazethapyr 0.5 and 1 L/ha and during the third harvest were Imazethapyr 0.5 and 1 L/ha, 2,4-DB 3 and 3.5 L/ha, and Bentazon 3 L/ha. Metribuzine 750 g/ha caused phytotoxicity in new-seeded alfalfa during all of the cuttings. In established alfalfa, 2,4-DB 3.5 L/ha was the best herbicide in density reduction of Lactuca, and the best treatment for decrease in Lactuca biomass were 2,4-DB 3.5 L/ha, Imazethapyr (Persuite) 0.5, and 1 L/h. The best treatment for increase in established alfalfa yield at first harvest was Imazethapyr 0.5 and 1 L/ha, at the second harvest were Imazethapyr 1 L/ha, Bentazon 3 L/ha, and 2,4-DB 3.5 L/ha, and at the third harvest were all herbicide treatments except for Metribuzine 750 g/ha and 2,4-DB 3 L/ha.
In new-seeded alfalfa, Metribuzine (Sencor) 750 g/ha, Bentazon (Bazagran) 3 L/ha, and Imazethapyr (Persuite) 1 L/ha were the best treatments in decrease of Sisymbrium irio, Descurania sophia and Malcolmia africana density. 2,4-DB (Butress) 3 and 3.5 L/ha was successful only in decrease of density of Malcolmia africana. The efficacy of Bentazon (Bazagran) 3 L/ha and Imazethapyr (Persuite) 1 L/ha was significant in decrease of Sisymbrium irio, Descurania sophia and Malcolmia africana biomass. Alfalfa yield loss was observed in response to Metribuzine 750 g/ha during all three harvests. In established alfalfa, 2,4-DB 3.5 L/ha with the highest ability in Lactuca density decrease and Metribuzine 750 g/ha with complete control of Sonchus were the best treatments. 2,4-DB 3.5 L/ha and Imazethapyr (Persuite) 0.5 and 1 L/h with significant decrease in Lactuca biomass and Metribuzine 750 g/ha with complete control of Sonchus were better treatments. Due to phytotoxicity of Metribuzine 750 g/ha, the yield loss of alfalfa was observed in response to that herbicide during all three cuttings. Therefore, efficacy of Bentazon, 2,4-DB and Imazethapyr depends on their dose and weed species. The same herbicides are recommended to increase alfalfa yield. Metribuzine could control weeds, but it is not recommended for weed control, because alfalfa yield decreased under the effect of this herbicide. In this study, Metribuzine was used as post-emergence. If Metribuzine was used as a soil-applied herbicide, better result can be obtained. It is necessary for supplementary studies for exact results.