During 2001 an experiment was established in three locations

of the central and northern areas of the state of Veracruz,

Mexico. The objective was to assess the effectiveness of the

formulated mixture of the herbicides picloram + fluorxypyr in

the control of Sida acuta Burm f., Croton reflexifolius Kunth

and C. cortesianus Kunth, three perennial weed species

common in tropical grasslands. The mixtures of picloram +

fluroxypyr at 40 + 40, 60 + 60 and 80 + 80 g a. i./100 l water;

picloram + 2,4-D at 64 + 240 and 96 + 360 g/100 l water and

picloram + metsulfuron methyl at 64 + 4 g/100 l water were

evaluated in a Randomized Complete Block Design with four

replications. The effect of the treatments on the control of the

three weed species and on the toxicity to the forage grasses

was determined. The best control of S. acuta and C.

cortesianus were obtained with the highest and medium rates

of picloram + fluroxypyr, with average values higher than

90%. This herbicide mixture had a significantly higher control

than the picloram + 2,4-D and picloram + metsulfuron methyl

treatments. With the highest rates of picloram + fluroxypyr and

picloram + 2,4-D, C. reflexifolius was controlled 55 and 46%,

respectively; these mixtures were statistically similar between

them. None of the herbicide treatments caused any toxicity to

the forage grasses. It was concluded that applications of at

least 60 + 60 g a. i./ha. of picloram + fluroxypyr are required

to have a good control of S. acuta and C. cortesianus.

Keywords: Sida acuta, Croton reflexifolius, Croton cortesianus, chemical control, 2, 4-D, metsulfuron methyl.