herbicide use on a drainage ditch that drains into an estuary, new zealand

agriculture brown care chemical clean control cultivation dessicate die dieing ditch drainage farming fence field freshwater glyphosate grass green gulley herbicide herbicides horticultural kill killer lawn liquid management method nature new not organic organophosphorus pesticides plant poison pollution residual round roundup soil spray sprayed systemic toxic treat treatment weed weedkiller weeds wire yellowing zealand