The risk of sheep mortalities from the toxic weed caltrop could be reduced by treating infestations with a registered herbicide.
A recent study by the Department of Agriculture and Food has proved that spraying caltrop (Tribulus terrestris) with a herbicide registered for use on caltrop will likely eliminate its toxicity to sheep.
Caltrop produces the toxin protodioscin, which causes liver damage in sheep, resulting in jaundice, rapid weight loss and usually severe photosensitisation.
Department veterinary officer Roy Butler said an analysis showed markedly reduced levels of the toxin in herbicide treated dead caltrop plants compared with green plants.
“Earlier this year we collected both green and herbicide treated dead caltrop plants from properties in the eastern grainbelt, which were sent to the United States Department of Agriculture Poisonous Plant Research Laboratory in Utah for analysis,” Dr Butler said.
“The results showed that the levels of protodioscin were about one fifth the level of the untreated, green samples.”
Dr Butler said the research confirmed what scientists suspected – that once sprayed, caltrop is not toxic to sheep.
“It has not previously been possible to advise producers with confidence that if they spray out caltrop, the dead plant will present much less, if any, risk to livestock,” he said.
“The US results have confirmed what we thought, providing growers with evidence to effectively control caltrop and protect their sheep.”
Last summer proved a particularly favourable season for caltrop in the eastern grainbelt and a number of producers reported sheep deaths.
Dr Butler said with recent rain, caltrop may proliferate again this summer.
“Sheep producers, particularly in the central and eastern grainbelt, should be wary of grazing sheep in any paddock where this rapidly growing plant is predominant,” he said.
“The signs of caltrop poisoning in stock can be similar to other livestock diseases that are reportable, such as Blue tongue virus and sheep pox.”
Dr Butler said producers should seek veterinary assistance if caltrop poisoning is suspected.
“It is important to confirm the diagnosis and enable the exclusion of trade sensitive diseases, such as Blue tongue virus and sheep pox which do not occur in Australia but share some of the clinical signs,” he said.
“This information is valuable as it supports verification of WA’s favourable animal health status, which enables market access for livestock and livestock products.”
Financial subsidies are available to producers from the department to encourage disease investigations, boost surveillance for early detection of emergency animal diseases and provide evidence of disease freedom for ongoing market access.
For more information contact your private or department veterinarian.
More information on caltrop is available on the DAFWA web site by searching for ‘caltrop’.
Media contacts:Lisa Bertram/Megan Broad, media liaison +61 (0)8 9368 3937