An local incursion of the dreaded black knapweed has triggered a swift and strong reaction from government authorities and will be stopped in its tracks, if this week's surveillance efforts and ongoing vigilance to eradicate the weed from NSW is successful.
The weed was spotted last month on the side on Bellevue Road, on the eastern outskirts of the Tenterfield township, by ecologist Clair Lock doing a floristic survey of rare species to support a development application. A specimen was originally submitted to the Queensland Herbarium for identification, triggering alarms and invoking an emergency response under the Biosecurity Act due to its classification at prohibited matter.
The weed is unlikely to have entered the state through the nearby Queensland border, as one would assume. Originally from Europe, it prefers cooler climes and is well-established in Victoria and Tasmania and parts of South Australia (as well as in the USA and Canada), and has not been found in Queensland.
It could have hitchhiked with hay transported from southern states, but how the 1000-strong Bellevue Road patch of the weed came to be established will probably never be known with any certainty.
The discovered outbreak has been dealt with by Tenterfield Shire Council, who will continue to monitor it, but on Wednesday 20 personnel from local and neighbouring councils and Local Land Services and Department of Primary Industries regions gathered in Tenterfield to launch an all-out assault on the weed before it becomes established.
The DPI's invasive species program manager Elissa van Oosterhout said while some participated to experience an emergency response, everyone was keen to deal with the weed well before it approaches the trigger point where efforts turn to containment rather than eradication.
The group gathered at Tenterfield Saleyards, not far from 'ground zero' on Bellevue Road, and divided into teams to check public lands and visit the 100 properties within a five-kilometre radius over the remainder of the week, to determine the size of the infestation and devise eradication measures. They'll be examining high-risk pathways like waterways, as the weed prefers moist ground. The groups are observing strict hygiene protocols before entering each property to avoid cross-contamination.
Property owners have already been made aware of the project, and Ms Oosterhout hoped they would take advantage of the help and expertise being offered to rid themselves of the problem. She also did a street walk in the CBD to educate the public, as only widespread vigilance will keep the weed at bay.
Anyone seeing the plant, on either public or private land, is urged to contact Tenterfield Shire Council on (02) 6736 6000 or the NSW Biosecurity Helpline on 1800 680 244, even if they're not sure. Identified black knapweed outbreaks will be dealt with by council at no cost to the landholder.
Black knapweed belongs to the thistle family and its flower resembles that of the scotch thistle (so prevalent in this district) but without the spines. At the moment it's most likely the flowers which will be noticed, but after rain the leafy rosettes of the young plants may be found.
It is not palatable to livestock (although the drought brings desperate measures). Spread is more likely from natural carriage of seeds through wind or water, or via root fragments if the soil is tilled, or transported on machinery or in fodder.
The weed is an 'allelopath', meaning it chemically discourages other plants from growing nearby, thereby decimating crops and pastures.
Interestingly the last recorded NSW incursion of black knapweed was back in 1903 in ... Tenterfield! Ms Oosterhout said while it's possible for so-called 'sleeper weeds' to suddenly emerge decades after the last plants were seen, it's very unusual for them to last more than a century.
It may be possible to undertake genome testing on samples from this outbreak and the earlier one, both held at the NSW Herbarium, to see how closely they are related. Ms Oosterhout said similar testing on a form of Salvinia that does not set seed in Australia, although it does everywhere else, traced all Australian specimens back to a single parent plant entering this country.