CSI techniques track down elusive weeds

Crime scene investigation techniques straight from the forensics playbook are helping track down some of the state’s most invasive weeds across NSW waterways and landscapes. The NSW Government is using environmental DNA (eDNA) to seek out the weeds we can’t see, including hidden and dormant Amazon frogbit, yellow burrhead, alligator and parthenium weeds. NSW Department of Primary Industries and Regional Development (DPIRD) scientists have sampled NSW waterways to test eDNA levels of Amazon frogbit, Limnobium laevigatum, in the Sydney, Illawarra and Shoalhaven areas. This year, NSW DPIRD weed researchers, Dr Karen Bell and Dr Xiaocheng Zhu, have returned four times to sample frogbit infestation sites where the weed was found near Wollongong in late 2023. “This frogbit work is part of a bigger project to develop eDNA techniques which support weed management and the effective detection and eradication of new weed incursions,” Dr Bell said. “We are investigating how the genetic material or DNA of target weed species can be extracted from water and other materials, which can include soil, pollen, faeces and air, to reveal where weeds may be hidden. “The aim is to increase the reliability of weed detection methods, improve interpretation of our results and test the potential of the new methods we are developing to measure eradication effectiveness.” Detecting the plant’s presence through its eDNA allows biosecurity and weed management teams to target unwanted weeds before they infest our environment and farmland. Early detection, intervention and weed control saves money, by eradicating the weeds or reducing their impact before they take over. NSW DPIRD is working with Illawarra Shoalhaven Joint Organisation (ISJO) to track frogbit eDNA throughout the eradication process and fine-tune their new eDNA detection method. ISJO Chief Weeds Officer, David Pomery, said eDNA is offering land and waterway managers a valuable new tool. “Frogbit and other weeds can be hard to detect as surveys for new incursions heavily rely on visual detection with support from weed officers, contractors and the public,” Mr Pomery said. “Visual monitoring of frogbit is hindered by the presence of a very similar looking species, Hydrocharis dubia, also known by the common name frogbit.” Amazon frogbit is a floating freshwater plant from Central and South America. It can rapidly invade and smother waterways and is a serious biosecurity threat. In NSW, frogbit is prohibited matter under the Biosecurity Act 2015. Anyone who becomes aware of or suspects the presence of prohibited matter must immediately notify DPIRD. Illegal dumping of aquarium or pond plants in waterways has caused frogbit infestations in NSW. Frogbit has been found for illegal sale in NSW aquarium shops, at markets and online. This plant must not be sold in NSW