Two field experiments were carried out in an experimental area of the FCAV/UNESP - Jaboticabal/SP, Brazil, aiming to observe imazethapyr residues in the forage of the alfalfa and to analyze the interference of monocotyledons and dicotyledons weeds. In the first experiment, the herbicide was applied at rates of 0,5 and 1,0 l of p.c./ha on the development stadium: bud sprouting, vegetative stadium, that is, before the total covering of the soil and beginning of the flowering of the alfalfa.. Since no herbicide residues were found in the alfalfa plants, they can be consumed by the animals, right after its treatment. In the second experiment, four treatments were established concerning the handling of courts of the experimental area and in the presence of weeds: 1) cut in the summer of 1996, without the weed presence, 2) cut in the winter of 1996, without the weed presence, 3) cut in the summer of 1997, with the presence of monocotyledons, 4)cut in the summer of 1997, with the presence of dicotyledons. The presence of weeds reduced the production of dry matter of the alfalfa. Concerning the values of the cellular wall, lower values of Hem (5,7) and Lig (5,1) and higher value of PB (26,1%) were observed in the plants picked in the winter, due to the largest proportion of leaves.
mendicago sativa L; competition