The Muster l INDUSTRY UPDATE
Drought, fire, floods. Then came the weeds. Prolonged and extreme drought conditions, followed by bushfires, floods and a year of good rainfall for most parts of NSW, have seen an explosion of weeds. Words DARREN BAGULEY
A
nyone travelling in NSW over the past year would have been struck by the explosion of colour in the landscape. Depending on the region, farms have been carpeted with the vibrant purple of Paterson’s curse, the striking yellow of cineraria or the white dots of parthenium weed. Philip Blackmore, Invasive Species Officer at NSW DPI, says “drought can devastate existing vegetation, removing competition for light, nutrients, moisture and space, which allows quick establishment of weeds when conditions become favourable. “Weeds can germinate from the seed bank straight after rain occurs, and their invasive ability allows them to grow and spread more quickly than other plants. Weeds can also thrive after fires and floods; dormant weed seeds can be triggered into germination by smoke and water. Together with the lack of ground cover that fire and floods cause and combined with follow-up rainfall, there can be dramatic increases in weeds after fires and floods,” Philip says. PROBLEM WEEDS
There are more than 300 species classified as weeds in NSW. However, farmers are also now seeing the high risk of serious new weeds being introduced to properties; as well as the increased growth of existing established weeds.
14
THE FARMER
For example, parthenium weed and tropical soda apple are two highly invasive weeds that have seen a resurgence in the past year. “Parthenium weed has been detected in several parts of NSW in connection to hay, grain, vehicles and machinery brought into NSW from Queensland. It invades pastures and crops, is unpalatable to stock, contaminates grain and fodder and causes severe human health issues, including respiratory problems and dermatitis,” says Philip. “Tropical soda apple can be introduced through livestock movements and germinate after fire. “New weeds can also be introduced as part of a restocking program or when stock return from agistment. Studies have shown that up to 12 per cent of weed seeds can pass through the digestive system of livestock and remain viable.” Landholders also have to deal with an increased weed burden of long-established weeds such as serrated tussock, flat weeds, wild radish, wild oats and other widespread established weeds that have always been challenging, but have become harder to manage while recovering from droughts, fires and floods. According to an LLS spokesperson, “Blue heliotrope is becoming a greater issue as it has capitalised on drought conditions and is competing
JUL - AUG 2021
with native and desirable introduced species both in farmland and in areas of environmental importance. “African lovegrass takes over pastures and can be a fire risk. It has not had the grazing pressure from livestock and wildlife that desirable species have had in the drought and it has been able to set seed, which is blown by wind and soon establishes in bare patches. “Silverleaf nightshade has seen a strong resurgence in NSW due to the favourable climatic conditions between the summer of 2020 and 2021, particularly in Riverina and Central West NSW. Silverleaf nightshade severely affects arable lands, causing 70 per cent loss in grain yields and up to 100 per cent loss in pasture production.” EVERY DISTRICT AFFECTED
Due to the drought, fires and floods being so widespread, not a single local government area in NSW has remained unaffected. On the North Coast and Northern Tablelands, tropical soda apple is problematic in Kempsey Shire Council, Clarence Valley Council, Coffs Harbour, Armidale and Rous County Council, particularly in areas where existing infestations were fire affected. Nambucca Valley Council, Bellingen Shire Council and Rous County Council have seen outbreaks of parthenium weed and, according to the DPI, co-ordinated responses
to eradicate those infestations and trace their sources are underway. Similarly North West NSW and the Northern Tablelands have had numerous new incursions at Tamworth, Gunnedah, Warrah, Croppa Creek, near Boggabri and Narrabri, and along the Newell and Kamilaroi Highways. New sites also occurred in the Upper Hunter around Blandford and Muswellbrook; and in the South East regions near Kiama and Berry; and in the Central West region near Parkes. Aquatic weeds such as water lettuce, water hyacinth and salvinia have caused damage to infrastructure such as fences and smothered pastures in floods. This has been a problem in all Local Government areas on the North Coast affected by floods. PLANTS OUT OF PLACE
A weed is a plant out of place. For example, bahia grass is sown as pasture in many parts of the North Coast and provides a valuable component of the feed base for many producers in areas of lower fertility. In areas of higher fertility, however, bahia
