This research was conducted at the Agronomic Experimental Station UFRGS, Guaíba, RS, Brazil, during 1978/79, in order to study the influence of environmental conditions during five day times of spraying on the performance of three post-emergence herbicides applied over three weed species and soybeans. In this fi eld expe riment the compounds used were acifluorfen, bentazon and dinoseb, and the weed species tested were Bidens pilosa L., Euphorbia heterophylla L., in two growth stages and Sida rhombifolia L., in one stage. The occurrence of low temperature contributed to decrease the degree of Bidens pilosa L. control with acifluorfen, while high air humidity increased the degree of Euphorbia heterophylla L. control, mainly when this species was sprayed with dinoseb. On the other hand higher the herbicide efficiency on a particular weed species, the lower was the influence of the environmental conditions on the results attained on control.
Soybeans; Bidens pilosa L.; Euphorbia heterophylla L.; Sida rhombifolia L.; hours of application