Weeds rampant: from hungry geese to scorching fires
THE main reasons for the global weed explosion
are global trade, the atmospheric increase in CO 2 ,
human interference in the nitrogen cycle, and climate
change—says US scientist Prof. Hal Mooney of Stanford
University, who gave a keynote address to the recent 15th
Australian Weeds Conference held in September in Adelaide. Since
1788, more than 30,000 species of plants have been introduced to
Australia, mostly ornamentals, and 3000 of which are now
reproducing freely in the wild. One that was introduced for its
excellent pasture attributes, rather than its looks, may now
actually have initiated a grass–fire cycle in the Northern
Territory. Researchers from Charles Darwin University presented
findings that showed over the past 12 years there had been a
significant reduction in tree canopy from scorching gamba fires in
their study site—meaning that this local impact could be
happening on a landscape scale.
Contact: Samantha.setterfield@cdu.edu.au
Magpie geese and para grass
KAKADU’s immense flocks of wild magpie
geese are under increasing threat from para grass—originally
imported as a ponded pasture for cattle—because it is
replacing native wild rice, a staple food for the goose. In
research presented by Dr Penny Wurm (Charles Darwin University and
TS–CRC), Dr Sean Bellairs and Beckie Kernich (CDU), Penny
revealed that para grass dominates wild rice by shading the soil,
preventing the rice seed from reaching the temperature it
needs to break its dormancy. The grass readily escapes into the
wild and invades floodplains, displacing wild rice, as well as
native water chestnut, driving the magpie geese from their once
productive feeding grounds. One study on the Magela Creek
floodplain found that the distribution of para grass increased by
some 300 ha in five years.
Contact: Penny Wurm, Tel: 08 8946 6355
penny.wurm@cdu.edu.au
Insect controls for mimosa
IN some good news at the conference however,
Mimosa pigra, one of the worst weeds in northern Australia,
is showing signs of slowing down. Dense, impenetrable infestations
currently cover 800 km 2 of floodplains in the Northern
Territory. Biocontrol measures have been trialled since 1979, with
14 insect species that feed exclusively on mimosa released. So far
success has been mixed, but new results are showing the amount of
mimosa seed in the soil in infested regions of the NT have shown
massive declines. Soil seedbanks are now around 10% of what they
were before biocontrol began, a sign that the insects are starting
to make an impact.
Contact: Bronwyn Routley, Tel: (08) 8999
2266
Plant recovery from herbicides
HOW do plants recover generally from
herbicides to control weeds? Researchers from CDU and the
TS–CRC presented preliminary results from an investigation
into the effects of glyphosate on tropical savanna woodland plant
communities depending on the time of year it was applied. They
found that spraying in both the late wet season and the early wet
season negatively impact on cover of shrubs, geophytes and
perennial grasses. In contrast, herbicides applied late in the wet
season produced an increase in cover of annual plants while
applications early in the season reduced annual cover.
Contact: Kristine Brooks, CDU, kristine.brooks@cdu.edu.au
Bellyache bush
BELLYACHE bush infests thousands of hectares of savanna lands
right across northern Australia and new trials have been looking at
how different grazing regimes affect the weed and how bellyache
bush can affect pasture yield. Dr Faiz Bebawi, from the Tropical
Weeds Research Centre at Charters Towers, presented findings that
showed that the mortality of bellyache bush differed significantly
between grazing regimes—and without pasture cover (including
improved and native), the weed is likely to dominate areas much
faster.
Contact: Faiz Bebawi Faiz Bebawi@nrm.qld.gov.au
