Persistence of biological activity of imazaquin and imazethapyr sprayed in two seasons of the year

Abstract

With the aim of estimating the persistence of imazaquin and imazethapyr soil biological activity in a dark red latosol in Maringá, PR, Brazil, experiments were carried out in two different seasons of the year (winter/spring - from July to October, 1999, and spring/summer - from December 1999, to March, 2000). The herbicides were applied at 150 and 600 g/ha, and soil samples from 0-2 cm depth were collected from herbicide-treated plots an no-herbicide check up to 91 days after application (DAA). In greenhouse, bioassays using cucumber and sorghum as test-species were carried out, sowing these two species in soil samples collected from the experimental field. Results obtained allowed to conclude that imazaquin displayed a longer soil residual effect, and that higher rates (600 g/ha) of both herbicides provided longer periods of persistence, despite the season of application. The inhibition percentage of biomass production in samples from spring/summer herbicide-treated soil decreased faster, when compared with winter/spring application. Cucumber was more sensitive than sorghum as bioindicator of imazaquin and imazethapyr soil biological activity