Controlling weed incursions critical for new pasture development

Such advice is important for temperate pastures (such as phalaris), annual winter legumes and tropical perennials. Dr Hackney stresses weed control is best achieved using a combination of tactics that include spray-grazing, spray topping, winter cleaning, in-pasture selective herbicides and a clean-up pre-cropping phase. 

Most weeds competitive with new pastures have relatively low hard seed levels and Dr Hackney notes their soil seedbank amounts can be near exhausted by their total seed prevention over two to three seasons before pasture sowing. There are no selective herbicides to remove annual grass weeds from perennial grass seedlings.

Weed control pre-sowing and post sowing are among aspects to be covered in a series of coming workshops across the Central West during two weeks, between February 14 and February 23, and will feature presentations by Dr Hackney, John Piltz (NSW DPI), Neil Ballard (WA pasture consultant) and Auswest pasture agronomist Frank McRae. 

Workshops will be at Eugowra and Bathurst on February 14, Dunedoo and Tooraweenah February 15, Forbes and Condobolin February 21, West Wyalong and Temora February 22 and Trangie February 23.  Phone Chris Robinson chris.robinson@lls.nsw.gov.au on 0447 636 129 to register.

Inadequate sowing rates are also a common problem in achieving success in new pastures and will be covered at the seminars. Pasture establishment is a numbers game said Dr Hackney. If seeding rates are too low, weeds have a greater opportunity to colonise areas between pasture plants. Seed cost is often as a major disincentive to increasing sowing rate, but in the overall cost of establishment is relatively small and increasing sowing rate by one to two kg/ha does not add a lot to overall expenditure.

Species and variety choice is also critically important and Belinda Hackney urges a lot of thought be given to species and variety choice, not just accepting what is readily available. For example, species such as cocksfoot and serradella are better suited to strongly acidic soils. Within species there are also adaptation characteristics to consider. For example, big differences exist between varieties of tall fescue and cocksfoot related to their degree of summer or winter activity and persistence. 

Soil fertility is also critically important. Recent surveys have shown the majority of paddocks in southern NSW have soil pH that challenge the survival of rhizobia responsible for nitrogen fixation.

If legumes can’t fix nitrogen, overall production is reduced and response to superphosphate will be restricted because of low soil nitrogen. The same surveys have also shown that while soil phosphorus is often adequate, soil sulphur levels are generally very low, which again restricts legume productivity.

In addition to the coming seminars pasture establishment is well covered in a newly released NSW DPI booklet “Temperate perennial pasture establishment guide: Steps to ensure success”.  

Authors include Belinda Hackney as well as Linda Ayres, Nathan Ferguson, Fiona Leech, Luke Pope (former staff of NSW DPI), Helen Burns, Jenene Kidston and Nigel Phillips (NSW DPI)

Next week. “Precision agriculture” for pastures.