16-001014-02A (Ultimate SCMMP)

     Terrestrial weeds
     Terrestrial plants grow on land and include the majority
     of living plants. Most terrestrial plants have well
     developed root systems and reproduce via flowering.
     Flowering terrestrial plants are characterised by a range
     of life forms including herbs (grasses, sedges, rushes,
     and forbs), shrubs, and trees.

     Bioretention systems, swales, and the exposed batter
     slopes of sediment basins and constructed wetlands are
     particularly vulnerable to the establishment and ingress
     of terrestrial weeds.

     Terrestrial plants can be either annual or perennial.
     Annual plants undergo a complete life cycle
     (germination, flowering, and death) within a year, and
     rely solely upon the annual production of seeds or soil
     seed stores to persist. Alternately, perennial plants live
     for more than one year and generally rely on their root
     systems to sustain the growth of the plant foliage.

     Annual weeds are particularly susceptible to control
     methods that prevent the plants from successfully
     flowering, as this reduces the seed bank required to
     re-establish the plants in the following year. Strategies
     that can be used to prevent flowering, include physical
     removal (hand pulling, grubbing), slashing, and chemical
     control.

     Similar control methods may also be used for perennial
     weeds, which do not rely solely upon the availability of
     seed to persist. If perennial weeds are physically
     removed, care must be taken to ensure that the entire
     root system is removed, as it is possible for the plant to
     re-establish from the remaining root fragments. This
     particularly applies to perennial grass species, which are
     characterised by rhizomatous root systems that enable
     the plants to rapidly spread and establish daughter
     plants.

     Physical removal methods are generally suitable for
     isolated plants or small infestations; however chemical
     control methods may be necessary for large weed
     infestations or when woody weeds such as shrubs
     and trees are present.

     Foliar spray and rope-wick application of herbicides
     are generally suitable for the control of herbs and
     small shrubs, whereas cut stump and stem injection
     are effective techniques for applying herbicides to large
     shrubs and trees. Consideration should also be given to
     the strategic use of selective herbicides for the removal
     of weeds. For example, grass-specific herbicides can be
     used to remove Kikuyu from among native grasses, with
     minimal damage to the native vegetation.




72                     Maintaining Vegetated Stormwater Assets Version 1