Farm Guide VIC : 2008 - 2009
66 Livestock Post-drought weed prevention Key points • The expected autumn-winter break coincides with the peak germination of many annual and perennial grass and broadleaf weeds. • During prolonged dry periods, protect pastures from post-drought weed invasion by maintaining them above the herbage and bare ground thresholds of 1,000kg DM/kg and at least 70%, respectively. One of the long-term consequences of prolonged drought is at the increased risk of weed invasion when the season finally breaks. Low herbage levels and increased areas of bare ground over summer make pastures susceptible to a range of weeds, which establish readily in the absence of effective competition. Grazing below the recommended thresholds also increases the risk of erosion from both wind and water, makes pastures especially vulnerable to overgrazing and places plants at risk of premature death. Landholders who are familiar with weeds on their properties can often trace their establishment back to a critical period, usually a prolonged drought period when pastures were especially vulnerable to weed invasion. Manage the weed risk What can be done to reduce the impact of weeds and ensure that they do not become established as a major problem? Essentially it comes down to two things. Firstly, to assess pasture composition to determine not only the range of pasture species present (both desirable and non-desirable) but, most importantly, their capacity to compete with weeds; and secondly, to describe and understand the life cycle of each pasture species present. By understanding when individual pasture components germinate, grow and set seed it is possible to identify the weak and strong points in its life cycle. For most if not all weeds the weak point is clearly during its germination and establishment phase, which for many species occurs during the autumn-winter period and why this period is critical to prevent weed establishment and spread. Farmers are encouraged to undertake pasture assessment in autumn to determine their vulnerability and competitiveness, and to plan and implement strategies to reduce the risk of weed invasion. Severely degraded pastures will require a period of rest after the autumn break. This strategy is consistent with methods that try to generate a feed wedge to take into winter. It is essential to earmark the pastures and paddocks that are most susceptible to weed invasion and rest them until they have at least 1500kg DM/ha. This creates the dual benefit of providing competition to the germinating weeds as well as growing a bulk of feed for the winter. While grazing rest is a vital tool, also consider the strategic application of fertiliser in order to boost the growth rates of the desirable perennial species, as well as the use of selective herbicides where appropriate. An integrated approach to pasture and weed management boosts the competitiveness of the desirable species while also targeting the weed component. Next steps • Get a copy of MLA’s Pasture management for weed control • Visit www.mla.com.au/edge to find out about the EDGEnetwork Weed Removers, Pasture Improvers workshop To find out about other MLA publications and workshops on weed and pasture management, visit www.mla.com. au/publications, email firstname.lastname@example.org or phone MLA on 1800 675 717.
2009 - 2010