Western Australia
July 6, 2006
Annual ryegrass toxicity is taking its toll, costing livestock
producers about $40 million a year according to
Department of Agriculture and Food
estimates.
Along-side chemical control of ryegrass, three biological
control options - Safeguard ryegrass, Twist fungus and
non-toxigenic Rathayibacter are showing the best chance
of success.
Contracted on a project funded by Meat and Livestock Australia
(MLA) Department development officer David Kessell will present
the options to producers at the Department’s Sheep
Updates on 13 July, sponsored by MLA and Australian Wool
Innovation Ltd.
Annual ryegrass toxicity (ARGT) is a disease of grazing
livestock resulting from the ingestion of annual ryegrass
seed-heads infected by the toxin forming bacterium
Rathayibacter toxicus.
Mr Kessell said the causal organisms of ARGT were spreading
throughout Western Australia after first appearing near
Gnowangerup in 1968.
“Recent surveys have shown the organisms are now widely spread
in the wheatbelt and mixed farming areas where annual ryegrass
is present,’ he said.
“Deaths have also occurred on the Swan coastal plain in animals
fed locally- produced hay.
“But, while the major visual impact is livestock deaths, this
only accounts for approximately five per cent of the overall
costs of the disease. There are subclinical effects on wool and
reproduction and suspected on meat production and feed
conversion efficiency.
“Daily monitoring of stock is costly and psychologically
draining on producers. There is also a large cost to export hay
producers through rejection of contaminated hay (currently from
1 bacterial gall/kg of hay).”
Mr Kessell said in winter, a number of herbicide options were
available to reduce the ryegrass populations in crops and
pastures. The sowing of Safeguard ryegrass was also a very
useful option for graziers.
In spring, the use of slashing or heavy grazing to remove
infected seed-heads before toxicity developed could vastly
increase the safety of affected paddocks. Spray-topping with
gramoxone or glyphosate at the correct times would also prevent
further development of toxicity and make paddocks safer to
graze, but both these treatments were very damaging to legume
seed set.
Mr Kessell said an integration of several biological control
options was likely to have the most success.
“Safeguard is a cultivar of ryegrass that has resistance to gall
production from the nematode Anguina funesta. For
Safeguard to have the greatest impact, it must be established in
at least a 3:1 proportion with the local ryegrass,” he said.
“Twist fungus (Dilophospora alopecuri) competes with the
bacteria for the nematode vector and plant host. Inside the
ryegrass, twist grows more rapidly inhibiting nematode and
bacterial gall production. Once established, twist will persist
and spread, has been shown to dramatically reduce numbers of
toxic bacterial galls, and is not adversely affected by commonly
used fungicides.”
“Even though there has been a late start to the season, anyone
who has purchased twist fungus should put it out as soon as
possible to ensure the greatest likelihood of successful
establishment. It won’t keep until next season.”
Mr Kessell said the combined effectiveness of the two approaches
was demonstrated at a number of sites around Western Australia
in 2005.
“In a particularly impressive case, on a farm near Beverley WA,
the treatment reduced toxic gall numbers from potentially deadly
to relatively safe, within one season,” he said.
Non-toxigenic Rathayibacter is a non toxin producing
species of the bacteria which is being assessed in quarantine
studies and may prove to be highly effective in the control of
ARGT. These bacteria grow more rapidly and have been shown to
displace the toxic bacteria.
A decision from AQIS to allow field trials is hoped for by the
end of 2006. Potentially these bacteria would be easier to mass
produce and apply than twist fungus. |