Power of pastures and fodder crops to lower weed numbers
A robust crop and pasture rotation and strong crop competition are very effective strategies in mixed farming operations to keep weed numbers low in grain crops. The flow-on effect of the low weed numbers is that there is less selection pressure on herbicides.
Michael and Leanne Molloy and their sons Josh and Matt run a fully integrated mixed farming enterprise on properties south of Wagga Wagga, NSW, where mixed species brown manure crops and legume pastures provide fodder for the sheep, boost soil fertility and control grass weeds.
The 1900-ha aggregation of farms in the Yerong, The Rock and Henty districts centres on a winter cropping program that includes 1100 ha of wheat, canola and barley harvested for grain, 550 ha sown to perennial legume pasture and 100 ha of vetch-mix fodder. The vetch-mix fodder crop is brown-manured, and the perennial legume pasture phase runs for 4 to 6 years, providing multiple benefits to the Molloy’s farming system.
The remaining 150 ha is less arable and more frost-prone, so these paddocks are cropped less frequently, staying in a perennial pasture phase of lucerne, tall fescue, Phalaris, and clover for about ten years.
The Molloys run 3200 merino ewes and a flock of merino wethers, which they use as a relief valve to lighten the stocking rate if conditions dry off. The sheep are an integral part of the cropping system, grazing on short-term perennial pastures, vetch-mix fodder crops and crop stubble to make the best use of the 520 mm average annual rainfall.
Annual ryegrass is the main weed on the Molloy’s farms, along with some broadleaf weeds, but overall, their farming system keeps weed numbers very low. In 2017, the Molloys purchased a new farm near The Rock, which had been cropped continuously for many years. Michael says it took a few years to bring the weed numbers down using their system, but the black oats and ryegrass seed banks have now been reduced to very low levels.
Using the WeedSmart Big 6 tactics keeps weed numbers low and reduces the risk of herbicide resistance in the Molloy’s mixed farming enterprise.
The Molloys use a short-to-medium crop rotation that includes a brown manure cover crop and a pasture phase. Generally, the crop sequence is canola, wheat, canola, wheat and barley, then a mixed-species fodder crop, followed by canola and wheat, then a 4- to 6-year legume pasture phase before returning to grain production.
The mixed-species fodder crop is usually vetch-based with other species such as buster radish, purple top brassica and arrowleaf clover to provide soil nutrition and structure benefits, and a cereal, such as Illabo wheat, to provide early biomass. This highly palatable and nutritious fodder is used mainly to finish the cross-bred lambs.
Michael sprays out the grass weeds and cereals from the vetch-mix in late August, then brown manures the paddock in late October, providing strategic control of annual ryegrass. Canola is sown the following season, serving as a double break for grass weed control. They can then plant wheat into a very low weed seed bank environment.
The legume pasture mix includes barley, lucerne, subclover and arrowleaf/balansa clovers. Two years prior to termination of the pasture phase, the annual grass weeds are spray-topped then the pasture is spray-fallowed (brown-manured) the following spring, leading into the crop phase.
There is less selection pressure on herbicides during the pasture phase than during the cropping phase – a valuable strategy to keep key herbicides working in the Molloy’s farming system long into the future.
The Molloys plant their crops on 250 mm row spacing using a tined planter with presswheels. They have a partial controlled traffic farming system where they sow with a 9 m wide bar and spray and spread on 27 m widths, but their harvester is not aligned with these wheeltracks.
They have conducted electromagnetic (EM) surveys combined with a comprehensive soil testing program to map areas of sodic and acidic soils across the farms. Using segmented soil testing for pH and sodicity, they identified three variable rate zones for gypsum and lime.
Canola is a vital crop in their weed management program. To maximise crop competition, they grow hybrid Clearfield canola varieties, ensure good soil health, fertilise to yield potential, establish an even stand at optimal plant density and sow their crops early. Michael has adopted recommendations from Rohan Brill’s research in the region, which clearly showed the yield and weed control benefits that flow from sowing hybrid canola early to increase early crop vigour.
Over summer, the sheep graze in all their cropping paddocks, utilising the stubble, sprayed weeds and volunteer crop plants. This grazing pressure on stubbles complements the summer weed control program.
You can read more about the Molloy’s farming system in their case study.
