Although glyphosate is considered a non- selective herbicide, several weed species show a certain degree of tolerance to the recommended rates. Weed species tolerance to glyphosate in areas with intensive application of this herbicide has been reported in Brazil. Thus, the objective of this research was to evaluate the influence of the herbicide glyphosate on the seedbank dynamics of the tolerant weeds Commelina benghalensis, Ipomoea grandifolia and Richardia brasiliensis; and the susceptible weeds Amaranthus hybridus and Galinsoga parviflora. The experiment was monitored during two years in the experimental area of Department of Plant Production of ESALQ/University of São Paulo, Brazil. Beginning with an initial density of 100 plants m-2 of each species, glyphosate was sprayed periodically under post-emergence conditions at the rates of 0, 0.36, 1.44 and 2.88 kg a.e/ha. The seedbank in the soil was estimated through seedling emergence evaluation and physical extraction from the soil. Seedbank of the tolerant species increased specially at lower rates of glyphosate. On the other hand, the seedbank of susceptible species decreased during the experiment, even at lower rates. In the last seedbank evaluation, the tolerant weeds presented almost 12 million of seeds/ha, while the susceptible weeds showed about four million seeds/ha. It was concluded that the intensive use of glyphosate can cause a weed shift in the area, increasing the frequency of tolerant weeds along the years.
tolerance; Richardia brasiliensis; Commelina benghalensis; Ipomoea grandifolia; Galinsoga parviflora; Amaranthus hybridus
