Mato Grosso and Paraná states are leading the way after sowing respectively 3.5pc and 4.2pc of their estimated areas in the 2020/2021 season, AgRural data shows.
Corn and wheat edged lower too, curbed by an advancing US corn harvest and caution ahead of widely followed US government grain stocks data on Wednesday.
The association last week revised down its forecast for Ukraine's 2020, sunflower seed output to 14-15 million tonnes from the previous estimate of 15 million because of poor weather.