Desempenho de foransulfuron + iodosulfuron e imazapic + imazapyr em biótipos de Bidens spp.

摘要

Bidens spp. especies are present in 74% of the farms of central plateaus of the state of Rio Grande Do Sul, Brazil. The species Bidens pilosa was the first weed to be documented as resistant to herbicides inhibitors of the enzyme acetholactate sinthase (ALS), in Brazil. Foransulfuron + iodosulfuron and imazapic + imazapyr are ALS inhibitors recently launched to use on the corn crop. Since, there is no record of the action of these herbicidas on resistant Bidens spp. biotypes, the objective of this work was to evaluate the performance of foransulfuron + iodosulfuron and imazapic + imazapyr on biotypes collected in several places in Brazil. Experiments were conducted in the greenhouse at Federal University at Rio Grande do Sul. Seeds of Bidens spp. had been sown in trays with capacity for 2000 ml, with soil:sand substratum (2:1). After emergence, seedlings were transfered to vases with 300 ml capacity and kept irrigated. When seedlings had reached the four leaved stage they were sprayed with the herbicides with rates from 0 up to 8 times the recommended dose. The experimental design was a complete random design with four replicates. At 21 days after the application it was evaluated the plant control. The results had been submitted to the analysis of variance and when evidenced interaction of biotype and rate, dose-response curves had been adjusted, for each biotype. The results confirmed difference of sensitivity to the herbicides between the tested biotypes. The biotypes susceptible to other ALS inhibitors had confirmed its susceptibility to the herbicidas foransulfuron + iodosulfuron and imazapic + imazapyr. But, the biotypes resistant to other ALS-inhibitors were also resistant to these herbicidas. The mixtures of foransulfuron + iodosulfuron and imazapic + imazapyr are new herbicidas for the corn crop but do not solve the problem of ALS-resistance in Bidens spp.