Pathclear Gun. Weedkiller has been specially formulated for gravel paths and drives. It contains a Systemic weedkiller and contact weedkiller to kill off all manner of existing weeds and residual weedkiller to prevent new weed seeds from germinating. It works by killing the existing leaves and roots, and creating a barrier in the soil preventing new weeds from growing for up to 3 months. It is effective against annual and perennial weeds.