Two trials were carried out to study the possibility of the reduction of glyphosate rates through the addition of different quantities of vegetal oil and urea as adjuvants. These treatments were studied on Panicum maximum plants at three differents qrowth stages. The experiments were conducted in 1990, in citrus orchards containing high densities of P. maximum. In the first trial, the glyposate was sprayed alone (1.80 kg a.e./ha) and at the rate of 1.44, 1.08 and 0.72 kg a.e./ha, plus vegetal oil at the rate of 1.0, 2.0 and 3.0 l/ha and urea at the concentration of 0.2%, 0.3% and 0.4% in the herbicide solution. A control plot was sprayed with pure water. In this essay, the P. maximum plants were 1.5m high. In the second essay glyphosate (1.08 kg a.e./ha) was sprayed alone and in mixture with vegetal oil (2.0 l/ha) and urea (0.3% on P. maximum plants at three differents growth stages. The stages were: a) 0.6m high at the start of the flowering and frutification, b) 1.5m high, full flowering and frutification stage, and c) 0,5m high from regrowth after cutting of old plants. The addition of vegetal oil (2.0 l/ha) was enough to make possible the glyphosate rate reduction to 0.72 kg a.e./ha, showing the same efficacy of the glyphosate rate of 1.80 kg/ha, sprayed alone. The addition of urea (0.2%) made possible to reduce in 0.36 kg a.e./ha the rate of herbicide. The herbicide’s efficacy was reduced in older plants, but it was very effective when applied over regrowth plants. The glyphosate when applied at the flowering stage, avoided development of the P. maximum seeds, reducing the seeds bank enrichment.
vegetal oil; urea