March 21, 2013
The Department of Primary Industries (DPI) is on the look out for Scotch thistle (Onopordum acanthium) in the North Central Catchment. DPI knows of one confirmed infestation in the Loddon region near the small township of Logan. DPI Biosecurity Officer Barton Roberts said Scotch thistle was a highly invasive annual or biennial herb which posed a significant threat to agriculture and the environment if left untreated. “The plant is unpalatable and can reduce a farm’s carrying capacity,” Mr Roberts said. If existing Scotch thistles are not treated and they become well established, pastures may be overrun as the large leaves smother its competitors. “Scotch thistle is a regionally prohibited weed in the North Central Catchment, meaning its distribution is considered limited but it has the potential to spread further. “It is therefore very important to determine the full extent of infestations of Scotch thistle in the catchment so DPI can plan management actions with the long-term aim of eradication. “In other parts of Victoria there are infestations of Scotch thistle ranging from 50-100 hectares, with some over 200 hectares in size. If left untreated Scotch thistle has the potential to spread across the south west of the North Central Catchment, into the Inglewood, St Arnaud, Avoca and Maryborough regions.” Scotch thistle can grow to two metres, with one main stem and numerous branches and broad spiny wings. Flowers are purple or mauve and leaves are spiny with dense white woolly hairs on the underside. Scotch thistle is often confused with other thistle species, especially spear thistle (Cirsium vulgare (Savi) Ten). The most obvious difference is the leaf and stem appearance, Scotch thistle is covered with a mat of white hairs giving it a white appearance, spear thistle has dark green leaves giving it a darker appearance.