Publicação on-line; 25 ref.; 3 tables; 2 illus.; Summary (En)

ABSTRACT
Background: Sourgrass (Digitaria insularis) is a highly disseminated
weed in Brazil. It is a perennial grass weed that has high infesting capacity
in agricultural areas and presents glyphosate-resistant biotypes. An
effective post-emergence control of sourgrass plants depends on their
phenological stage at the time of herbicide application.
Objective: This work was developed with the objective of evaluating the
effect of the sourgrass phenological stage at the time of herbicide
application on the efficacy of ACCase-inhibiting herbicides.
Methods: Two independent experiments were conducted under
greenhouse conditions to evaluate two ACCase-inhibiting herbicides:
clethodim, and haloxyfop. The treatments were applied using a
completely randomized block design, with an 8×4 factorial arrangement
consisted of 8 herbicide rates (4, 2, 1, 1/2, 1/4, 1/8, and 1/16 times the
recommended rate, and a control plot without herbicide application) and
four phenological stages of sourgrass.
Results: The development of sourgrass plants after tillering decreased
the efficacy of the herbicide molecules; however, clethodim and haloxyfop
were efficient to control sourgrass at earlier developmental stages.
Morphological, anatomical, and physiological changes in older plants may
explain the lower susceptibility to herbicides.
Conclusions: Other control techniques should be considered for
sourgrass plants at later developmental stages, such as sequential
application or herbicide mixtures, to increase the efficacy of ACCase
herbicides.

Keywords:
Digitaria insularis
clethodim
haloxyfop
management
resistance