Amanda Cook1 and Ian Richter1
1SARDI, Minnipa Agricultural Centre
Peer review: Nigel Wilhelm1
- Under the production regimes of upper EP stubble management is unlikely to impact negatively on performance of pre-emergent herbicides targeting grassy weed control, with adequate water rates.
- If grass weeds are an issue in paddocks with high stubble loads (greater than 50% stubble cover), removal of some stubble may be a benefit to maximize the herbicide activity and grass weed control. The chemicals which may be influenced by high stubble loads include trifluralin, triallate, pyroxasulfone, prosulfocarb and metalochol products.
- In-crop germination patterns are later for barley grass in Minnipa Agricultural Centre paddocks, which is limiting early grass control with pre-emergence herbicides.
- If you expect most of your grass weeds to emerge straight after sowing maybe 2L/ha Trifluralin (plus an added chemical) is the best value for your system.
- If you have a dormant/later germinating population, and aim to reduce the seed bank, you may be better investing in some of the more expensive chemical mixes even though they may cost more in the first season.
Why do the trial?
The GRDC Maintaining profitable farming systems with retained stubble – upper Eyre Peninsula project aims to improve farm profitability while retaining stubble in farming systems on upper Eyre Peninsula (EP). Weed control in stubble retained systems can be compromised when stubbles and organic residues intercept the herbicide and prevent it from reaching the desired target, or the herbicide is tightly bound to organic matter. Reduced herbicide efficacy in the presence of higher stubble loads is an issue for pre-emergence herbicides. Current farming practices have also changed weed behavior with a shift in dormancy in barley grass genotypes now confirmed in many paddocks on Minnipa Agricultural Centre (MAC) (B Fleet, EPFS Summary 2011, p 177). As a part of the stubble project this trial was undertaken to assess herbicide efficacy in different stubble management systems.
How was it done?
The 2016 trial was sown into paddock S3N, on 30 May into good moisture conditions with Mace wheat @ 60 kg/ha and DAP @ 60 kg/ha. The stubble treatments were; standing stubble with burnt windrows (burnt on 31 March) and slashed stubble also with a burnt windrow (slashed on 8 April). The trial area received a knockdown of 1.2 L/ha of Roundup Attack on 29 May. Fifteen chemical treatments, mostly pre-emergent (applied on the 29 and 30 May) and some post emergent were individually mixed in small pressure containers and using a shrouded boomspray at 100 L/ha of water. Treatments included different rates and mixes of Trifluralin, Metribuzin, Diuron, Avadex, Monza, Sukura and Boxer Gold.
The trial was sown at 3-4 cm depth with an Atom-Jet spread row seeding system with press wheels.
In 2016 the Minnipa Agricultural Centre received 391 mm of rainfall, with growing season rainfall of 268 mm. Measurements taken were stubble load pre-seeding, plant emergence counts, early, in- crop and late grass weed counts and dry matter production, grain yield and grain quality.
Thanks to Ben Fleet, Andy Bates and Nigel Wilhelm for help with this trial and to Sue Budarick, Tegan Watts, Lauren Cook and Katrina Brands for their help collecting and processing samples. Trial funded by GRDC Maintaining profitable farming systems with retained stubble – upper Eyre Peninsula (EPF00001).