Abstract: The present invention relates to a method to increase the effectiveness of an imidazolinone herbicide to suppress weedy forms of rice growth used with imidazolinone tolerant rice strains. This method involves applying an imidazolinone herbicide to imidazolinone tolerant rice strains in a field and applying either a propanil based herbicide or a thiobencarb herbicide to this rice crop, wherein the herbicide includes a synergistically effective amount a herbicidally inactive ingredient. The propanil based herbicide synergistically affects the activity of an imidazolinone herbicide by increasing the effectiveness of an imidazolinone herbicide used with the rice to suppress weedy forms of rice growth, such as red rice.