Currently, only two herbicides, Londax® (bensulfuron) and Taipan® (benzofenap) are
available for the effective control of all four major broadleaf weeds infesting NSW rice
paddocks. Prolonged and widespread use of these two herbicides in the rice growing regions
increases the threat of herbicide resistance. The low likelihood of new herbicides in the
foreseeable future increases the impact of herbicide resistance on the Australian rice industry.
Allelopathy, chemical interactions between plants, is an alternative control option. Weeds
could be controlled by using crops which have been developed to exert their own weed
control by releasing chemicals into the soil. These naturally occurring compounds could play
a valuable role in an integrated weed management system, potentially reducing the amount of
synthetic herbicides required for weed control.
In rice, the potential use of allelopathy in weed control has been explored by several
researchers worldwide. Funding for work on allelopathic potential was provided by the Rice
CRC as they recognised that the Australian weed community is very different and many of
the weeds infesting rice paddocks are typically Australian problems not likely to be tackled by
international research groups.
Twenty-seven rice cultivars were examined in the laboratory for their allelopathic potential
against several currently important and potentially important rice weeds in Australia, namely
barnyard grass (Echinochloa crus-galli), dirty dora (Cyperus difformis), lance-leaved water
plantain (Alisma lanceolatum), starfruit (Damasonium minus), arrowhead (Sagittaria
montevidensis) and S. graminea. Weed root growth inhibition ranged from 0.3 % to 93.6 %
of the control depending on the cultivar and the weed species being tested. One weed was
actually stimulated by Langi. Several rice varieties significantly inhibited root growth of
more than one weed.
A field trial using starfruit as the test species was conducted to see if those cultivars which
inhibited starfruit in the laboratory experiment also inhibited starfruit in the field and to
determine whether allelopathy was an important factor in the resulting field performance.
Twenty-four cultivars were used in a field trial based at the Yanco Agricultural Institute.
Starfruit dry matter was measured as an indicator of weed inhibition. It was found that there
was a correlation between laboratory and field results, and that allelopathy was an important
contributor to field performance of a rice variety.