Arrowhead

Sagitiaria graminea var. platyphylla

Arrowhead, Sagitteria graminea - is an attractive, emergent, erect, aquatic perennial plant that has become widely dispersed throughout the irrigation areas of south-eastern Australia, particularly in northern Victoria where this aggressive plant has spread rapidly in supply channels and drains impeding water flow.

  • The presence of Arrowhead in northern Victoria was first documented in 1962 after being identified in the Nine Mile Creek at Wunghnu. By the early 1970s it had spread into channels and drains around Nathalia and Numurkah and soon after to the Shepparton Irrigation Area.
  • From literature searches it appears that Arrowhead, a native plant of North America, only displays aggressive growth habits in the more temperate regions of Australia.
  • In Queensland Arrowhead is regarded as a useful plant in re-establishment of wetlands and for waste water treatment.
  • However, in northern Victoria and southern New South Wales it is regarded as a pest plant in irrigation systems and natural waterways.
  • Arrowhead is not easily controlled by either mechanical methods or by the herbicides registered for use in aquatic situations.

A Pretty Nuisance
Arrowhead is a rhizomatous perennial growing up to 150 cm tall, introduced from the Americas.

  • It has triangular stems in cross-section up to 75 cm long and emergent leaves up to 35cm long.
  • It also has submerged strap-like leaves up to 50 cm long.
  • The flowers are on a leafiess stem in whorls - the upper whorls are male and the lower whorls, with 3 white petals, are female.

The plant has the ability to spread rapidly by way of rhizomes and seed dispersed by water and water-birds. It can also spread when attempts are made to mechanically remove the plant which often results in the breaking up of rhizomes.

The plant germinates from late winter to early spring and the flowers appear from mid to late spring. Arrowhead may then continue to reproduce from rhizomes and appear in the three leaf stage throughout the summer alongside mature plants. It favours static to slow flowing water up to one metre in depth and readily establishes on clay silt beds.

Efforts to control Arrowhead
Despite the concerted efforts of Goulburn-Murray Water, and its predecessor authorities, Arrowhead has continued to spread and has continued to populate new areas within Northem Victoria. It is now prevalent in the Shepparton and Murray Valley Irrigation Area. Infestations have also appeared in the Central Goulburn, Pyramid-Boort and Torrumbarry Irrigation Areas.

The treatment option has been to spray the Arrowhead immediately following the end of the irrigation season, after draw-down, with 2,4-D amine. Some spraying is conducted during the irrigation season, when the plant is most susceptible, however with an allowable residue limit for 2,4-D in irrigation water of 0.1 mg/L, little effective spraying can be done.

Control is more easily achieved in farm channels as there are more options for the use or disposal of the treated water. After spraying, the channels can be drained with the water being used on permanent pasture or run to waste.

Research
There is no doubt that Arrowhead has spread rapidly in the irrigation areas and natural waterways in the past five years, due mainly to the fact that although the use of 2,4-D amine is the recommended treatment, it is far from being completely effective. Another factor is the difficult situation in which the herbicide has to be applied - always in water where residues are a problem.

Because of the limitations of 2,4-D in irrigation water there is a need to find an alternative treatment. The treatment needs to be one that can be safely used in water during spring and summer when the plant is actively growing.

Goulburn-Murray Water is carrying out an extensive trial program on Arrowhead to look at a number of new and some existing herbicides for efficacy value. The trials will cover all aspects of rates, timing and application techniques.

A joint project between Goulburn-Murray Water, Murray Irrigation Ltd and the CSIRO Division of Irrigation Research has been established to investigate methods of effective control of Arrowhead in irrigation systems, primarily in southern NSW and northern Victoria.

For more information, please feel free to contact us.