Growth Analysis of Sourgrass: Does Herbicide Resistance Affect Its Development?

Sourgrass (Digitaria insularis) is highlighted as one of the most troublesome weeds in Brazilian agriculture. The growth analysis of the species and biotypes with resistance to glyphosate are preponderant to support management strategies. In this way, the aim of this work is to compare the growth of biotypes resistant and susceptible to glyphosate, and to characterize the species growth in field conditions. The greenhouse experiment was installed in randomized blocks design, in factorial scheme 2 × 10, with eight replications. Factor A comprised the biotypes, and factor B the fortnight evaluations. The dry mass of roots, stems, leaves and shoot were assessed, besides leaf area and plant height. From these variables, the relative growth rate, net assimilation rate and leaf area ratio were calculated. For the field experiment, the same variables were assessed and the same parameters were calculated, without distinction on resistant or susceptible biotype. The biotype with resistance to glyphosate did not show adaptative disadvantages compared to the susceptible one. In this way, it is necessary to prevent the entry of resistant biotypes in cropped fields, as once established the area may not naturally return to the initial frequency of susceptible biotypes. Sourgrass shown slow initial growth and dry mass accumulation up to 42 days after emergence, indicating that control of this specie should be performed preferably before this period.