Herbicide Trials for the Control of Parrotsfeather

Parrotsfeather (Myriophyllum aquaticum (Vell. Cone.) Verde.) is an introduced aquatic weed that forms nuisance growths in drainage systems, wetlands and shallow lakes and is a species with limited or ineffectual control options in New Zealand. In the first year of trials five different herbicides were tested for their efficacy against parrotsfeather under culture conditions. The triethylamine salt of triclopyr (3,5,6-trichloro-2-pyridinyloxyacetic acid) was the most effective product and in the second and third trial years it was compared with glyphosate (N-phophonomethyl) glycine) (the product currently used in New Zealand for parrotsfeather control) and evaluated over a wider range of concentrations. Results indicate that triclopyr is effective at controlling parrotsfeather under contained experimental conditions, reducing biomass to zero (or near), with little or no plant recovery in contrast to the results for glyphosate. Under field conditions triclopyr has successfully reduced the cover and presence of parrotsfeather.