Hi Georgi,
As the game allowed you to fuel and pick up the bushcutter, you should be good to go with cutting down the bushes. So when you take the bushcutter out of inventory and click it onto the gear symbol over the bushes, nothing happens?

Are you close enough to a saved game at the point where you first examined the bushes, that you can go back and replay this part through again? Sometimes a replay will shake something loose.