Bushland Weeds Manual - Environmental Weeds Action Network

• Animals can carry grass seeds on their skin and
fur. Seed bracts and/or awns may have sticky
hairs, hooks or spines that aid adhesion. Ingestion
also plays a role in grass dispersal. Grasses
evolved with grazing and several authors have
noted seeds are voided intact (Davidse 1986).
Dogs, horses, native animals and humans
(among others) readily disperse seeds along
bush tracks. Horses can spread grass weeds
from paddocks into bushland, depositing seed
with their manure.
• Human activities including inappropriate
management practices, provide additional
mechanisms for grass weed dispersal:
Grading drags seed (and tillers) along road verges.
Slashing during flowering spreads seed with an
explosive action.
Lawn clippings dumped in bushland often
contain grass seed.
Soil seedbanks: Seedbanks consist of dormant seed,
which is ready to germinate given the appropriate
environmental cues. Dormancy allows seed to persist
in the soil in the absence of further seed rain.
As a general rule grass seeds are not considered to be
persistent within the soil. However, there are
exceptions. Numerous grasses have a soil seed life
greater than five years and not surprisingly many of
these are widespread weeds (eg. Fountain Grass and
Barnyard Grass). Poa pratensis and a number of
Setaria species are known to remain viable for at least
39 years (Baskin and Baskin 1998). Environmental
factors, including temperature, moisture and light
intensity can induce dormancy in seeds. For example,
deep burial induces dormancy in Wild Oat seed,
increasing its longevity from six months to anything up
to ten years (Baskin and Baskin 1998, Nugent et al.
1999). Dormancy is broken when the seed is returned
to the surface through soil disturbance.
For many species, seed longevity is not understood
and yet it is invaluable information when making
management decisions. The length of a control
program is largely determined by seedbank
persistence. The shorter lived the seed, the more
rapidly a grass infestation can be controlled
(provided the source is no longer
present or is also managed).
Chapter 3 Grass Weeds
Vegetative reproduction
Vegetative reproduction as a strategy in grasses is
most successful in moist, nutrient-rich conditions
(Briske and Derner 1998). Under these conditions
rhizomatous and stoloniferous grasses can easily
establish roots and rapidly disperse rhizome and
stolon fragments in soil and down streams. In Reed
Sweet Grass (and possibly other species), shoots of
young plants can be vegetative or flowering. However,
once established, the majority of new shoots produced
are vegetative. This strategy allows the plant to quickly
colonise new areas by seed, whilst increasing the
density of established plants (Department of Primary
Industries Water and Environment 2001).
Tussock-forming grasses may also propagate
vegetatively. Tillering is responsible for each season’s
new growth and the expansion in tussock area
(Hannaway et al. 2000). Tillers are also referred to as
sprouts, shoots and daughters and may break off when
disturbed.
If resources are scarce, management should focus
on controlling the invading edge(s) and new or
isolated populations.
Grass growth stages
As with all weeds the timing of grass control measures
is important. Active growth is required for herbicide
uptake and slashing can enhance leafy growth or result
in defoliation, depending on the growth stage. In most
grasses (sterile grasses are the exception) there are
three main stages of active grass growth: Vegetative,
transition and flowering.
• Vegetative growth involves the production of
shoots, mostly leaf blades but also stolons and
rhizomes. Herbicides are best applied at this stage,
while slashing usually results in increased
production of leafy material.
vegetative transition boot stage
flowering
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