PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Environmental weeds
Weed Types
Environmental weeds, unlike other weeds
invade natural plant communities without the
need for disturbance by human activity, fire,
altered drainage, added nutrients, cultivation,
grazing, etc (page 415). They are mainly introduced
species but some native species have spread
outside their natural range, eg golden wreath wattle
(Acacia saligna) from WA is now found in bushland
along the NSW coast.
Occur as a range of trees, shrubs, herbs,
grasses, creepers or climbers, aquatic plants, but are
mostly garden escapes, eg privet (Ligustrum
spp.), lantana (Lantana camara), English ivy
(Hedera helix), pampas grass (Cortaderia sp.),
periwinkle (Vinca major). There are nearly 1,000
species of environmental weeds in Australia, but
only 52 species have been selected for the national
list (page 415). Many are still being grown and
promoted by the industry. Each state/territory/region
has its own lists of environmental weeds.
Environmental weeds may also be:
– Noxious weeds, eg some willows (page 417).
– Agricultural weeds, eg blackberry (Rubus
fructicosus) and St John’s wort (Hypericum
perforatum) (page 413).
– Weeds of National Significance (WONS), eg
bitou bush (page 415).
– Sleeper weeds that have not yet increased their
distribution significantly and could be controlled
before numbers explode (page 414).
Impacts
Weeds threaten indigenous plant and animal biodiversity
by affecting their natural regeneration and
survival, ie food sources, shelter and habitat.
They threaten the existence of already endangered or
vulnerable species of flora and fauna. Plants may
become extinct (Sindel 2000).
They are of particular concern in areas dedicated for
conservation purposes.
They impact on public lands, State Forests, National
Parks, Botanic Gardens recreational areas, and
remnants of native vegetation on private land.
They can impede water flow in wetlands and river
systems, alter the habitat for wetland fauna, deplete
available nutrients, and alter soil fertility. Impede
tourism.
Some are poisonous or unpalatable to stock.
Annuals are considered to do less long term
ecological damage than woody species.
Exotic grasses moving into native grassland in poor
condition contribute to their decreasing biodiversity,
sustainability and are a fire hazard.
Fig. 256. Environmental weeds.
Left: Blackberry (Rubus spp.). Right:
Prickly pear (Opuntia spp.) controlled
by cactoblastis caterpillars in Qld.
Weed biology
Reproduction. Weeds reach maturity quickly.
They produce large amounts of seed or vegetative
propagules, and may be able to self–pollinate or
pollination is not required.
Overseasoning. Large seed banks, eg 75000 seed/m 2
of perennial veldt grass have been found in WA after
fire; also as tubers, rhizomes, deep roots, etc.
Spread efficiently. Birds and flying foxes eat fruit
and seed which is carried to nearby bushland. Livestock,
pets and people carry seeds from gardens to bush on fur,
clothing and shoes. Garden waste is dumped over back
fences or in waterways. Wind can blow seeds many
kilometers. Seeds and plant parts can wash down drains
into waterways where they grow and spread. Some have
branches which can break off easily and are washed
downstream and take root forming new infestations.
Seeds and plants are carried in soil on vehicle tyres,
tools, machinery. Floral arrangements. Plants for sale.
Conditions favouring. Rainfall is the most
important factor determining the possibility and extent
of woody species. Each environmental weed has its own
conditions which favor its spread and development.
Environmental weeds do not need disturbance but may
need several favorable seasons to establish. They
tolerate drought, frost, salt, low nutrients. Predicted
climate change may favor new weed species, but others
may become less important. Plants being bred for
drought tolerance may be the next generation of
environmental weeds. Tussock grasses invade
areas damaged by fire and loss of canopy cover.
Management (IWM)
Many countries have lost their natural biodiversity and
most of their flora has come from naturalized species from
other areas, and so do not attempt to manage invasive species.
Australia is one of the very few countries of the world that
try to do so (Thorp 2008) and aims to prevent incursions
of new weeds, detect new incursions quickly (making
eradication possible), contain spread of existing weeds and
re-habilitate disturbed ecosystems.
1. Planning ahead and site assessment is essential.
There are many programs in which you can participate
(page 471), training programs are available (page 430).
2. Crop, region. Obtain information on environmental
weeds and their management in your local area.
Contact your local council.
3. Identify those present at various stages of development,
eg seedlings, flowers, seeds, etc. Some environmental
weeds especially grasses, can be difficult to identify. You
must be sure it is a weed, many grasses are native to their
area. Consult a diagnostic service if necessary (page xiv).
4. Monitor environmental weeds to determine their
distribution, spread and later the effectiveness of
control programs (page 429). Methods include using the
National Classification System of Mapping for WONS,
satellite imagery, low altitude aerial photography and
hard slog, ie utes, canoes by Weed Warriors, Landcare
groups. Willows have been mapped by all these methods.
5. Threshold. There may be a nil legal threshold for
certain weeds in your area, otherwise construct your
own, deciding how much invasion you can tolerate,
aesthetically, economically or environmentally.
6. Action. Environmental weeds are difficult to control.
Address the causes of weed invasion.
Prioritise weeds for control. Eradication of most
environmental weeds is not possible. New arrivals
stand some chance of being eradicated,
eg Koster’s curse in the NT. Be aware of potential
sleeper weeds, eg lobed needlegrass.
Prioritize vegetation areas, eg sensitive areas
dominated by native vegetation may be maintained
weed-free, in others areas their spread prevented,
etc. Lightly infested areas may be treated prior to
areas with heavier infestations.
Re-vegetation of sites is challenging but essential.
Act co-operatively with local government, landowners,
suburban householders to control and
eradicate environmental weeds in local bushlands.
Resources are required.
7. Evaluation. Review your IWM program to see how
well it worked. Recommend improvements.
470 Weeds - Examples of weed situations