Wimmera grower aims for zero soil disturbance for weed control
Tim Rethus and his brother Luke farm with their father Geoff and workers Glenn and Dale in the central and southern Wimmera, where they are contending with Wimmera annual ryegrass, brome, wild oats, vetch, bifora, sow thistle and prickly lettuce.
“Our approach to weed control centres on keeping weed germination levels low and using diverse farming practices,” says Tim. “Dad was an early adoptor of minimum tillage back in the early 1980s and we have progressively moved to farming systems that involve less and less disturbance. One of the major benefits is that we are leaving the weed seeds on the soil surface where they are exposed to the weather and don’t have the soil contact they need, and this really reduces weed seed germination.”
A key element to the Rethus’ success is their determination to achieve near-zero disturbance at planting. When they adopted a 40-foot CTF system in 2008 their min-till single disc seeder did a good job and reduced soil throw but ten years on, the removal of machinery traffic from the cropping zone had led to the single discs often stalling in the softer soil and the depth control was no longer adequate.
This led the Rethus’ to invest in a zero-till precision planter to provide more precision at planting, including inter-row sowing for lentils, and to make best use of the newest chemistry available.
“This precision seeder was a good unit but it was complex and didn’t suit all our crops,” says Tim. “So, we decided to combine the precision row units with twin-disc openers on a new 80-foot NDF frame but use an air-seeder to deliver the seed.”
To further reduce soil throw, residue managers are not used. Instead ‘PTT Sabre-tooth’ discs are used to cut through the residue and reduce pinning. The two discs are slightly different in size, so they rotate at slightly different speeds, providing a cutting action to keep residue out of the seeding furrow.
“Adding side-shifting rams to the toolbar means we can also inter-row sow our lentils and we have a seeder that meets all our requirements, especially in terms of maintaining low weed seed germination at seeding while still sowing at 15-inch row spacing.”
The seeder also has moisture sensors along it that are linked to the depth control of each individual row to try and put all of the seed in the same level of moisture, ensuring an even strike.
The Rethus family practice a diverse crop rotation of wheat, barley, durum, canola, lentils, beans and oats, and use shielded spraying, hay production, brown manuring, spray topping and diverse herbicide strategies to minimise weed seed set. Tim says the reality of herbicide resistance means non-chemical tools are very important to maintain low weed numbers and this is one of the driving forces behind their efforts to fully integrate hay production into their CTF system.
“Within the rotation we usually have about 35 to 45 per cent legumes for their soil health benefits and the additional herbicide options available,” he says. “We practice chemical double-knock and mix and rotate our chemistry, realising that herbicide resistance is inevitable but we can delay onset and do all we can to maintain low weed numbers.”
The Rethus’ herbicide program starts with a pre-sowing double-knock where the pre-emergent is mixed with the paraquat if the season permits. They aim to apply the pre-emergent as close to crop emergence as possible so very little of the active life of the herbicide is wasted, this is particularly important when dry sowing so they delay application of the pre-emergent until breaking rains fall.
They mix and rotate pre-emergents where possible and are careful when planting two cereal crops in a row to not use Sakura both times, favouring Boxer Gold for barley crops. Legumes offer a number of Group C options to rotate between and in oaten hay they have found Dual Gold and diuron is a good mix provided care is taken to use the correct rate for different soil types.
In-crop they use multiple modes of action where possible, with legumes presenting serious limitations for in-crop broadleaf weed control due to the limited products available.
At the end of the season cover crops are terminated using multiple modes of action and a double-knock and lentils, canola, and sometimes barley, are crop-topped.
The Rethus’ routinely test weeds for susceptibility to the herbicides used across the cropping program to ensure they are using effective products and mixes. They use either a quick test in season or seed test at harvest if there are unusual weed escapes.
To avoid producing herbicide resistant weeds along the farm’s roadsides and tracks the Rethus’ choose to mow, rather than spray, the vegetation growing there.
For the last 15 years hay production has been an important mechanical control method to stop weed seed set – particularly for annual ryegrass. The Rethus’ will do up to three years of hay production in a row to drive down the ryegrass seed bank before returning to the grain cropping rotation.
“We run a controlled traffic operation and that makes hay production challenging,” says Tim. “Over the years we have developed systems and machinery that make it possible to keep to the wheeltracks throughout the hay-making process.”
“We use a front-mounted and side-mounted mower/conditioner to make three small windrows per CTF pass. The three windrows across the 40 ft CTF run are then raked together ahead of the baler. This provides a solid, constant feed into the baler travelling along the CTF wheeltracks, from crops that produce a biomass of typically 7 to 8 t/ha.”
“The final trick is to move the bales from the centre of the wheeltracks to the side so they can be picked up by the stacker. Our uncle built a hydraulic lifter that is mounted on the front of the tractor and simply lifts each bale and places it to the side where it is picked up by the stacker running behind the tractor. We stack all the bales at one end of the paddock making it easy for the telehandler operator and truck drivers,” he says. “We can bale, stack and store 600 bales a day this way without running off the CTF wheeltracks.”
In-crop, the Rethus’ use a camera-guided shielded sprayer for inter-row spraying in lentils. The Crop Stalker recognises the crop rows and follows between them, not relying on the crop to guide the shields.
Crop rotation is also used to manage persistent hard-seeded weeds, such as seven years without lentils for vetch control and four years without barley for wild oats control. Tim has found that even when they leave out their most profitable crop, lentils, for an extended period the paddock can remain very profitable.
“Another strategy we use for stopping seed set is to include multiple termination dates in the rotation, so the crop-topping, brown manuring and hay cutting all happen at different times,” says Tim. “Adding another layer of diversity reduces the selection for early maturity in weeds.”
Vetch has long been the brown manure used to build soil health but the Rethus’ are now using a multi-species cover crop for even better soil outcomes and reducing the build-up of vetch seed, which is a persistent weed in their system.
When it comes to crop competition the Rethus’ CTF system is set up for 38 cm (15 inch) row spacing, so they look for other ways to increase the crop’s competitive advantage. Starting with clean seed, their highest priority is minimal soil disturbance at sowing and maintaining standing stubble throughout the rotation. With the seeder only disturbing a very narrow band of soil there is little stimulation of weed seeds to germinate between the rows.
“We also sow early to take advantage of warm soils for maximum early growth and choose competitive varieties such as RGT Planet barley, Jumbo II lentils and hybrid canola,” says Tim. “It is very important that the crops we grow reach canopy closure by the time the pre-emergents have run out, and investing in good crop nutrition to support high biomass production in good years pays off.”
Tim and Luke are avid adoptors of new precision agriculture tools to map weeds, in-crop green-on-green spot spraying with best chemical rates to target persistent weeds like vetch, bifora, wild oats and brome and spot spraying summer weeds to reduce chemical use.
The Rethus’ robust integrated weed management system incorporates all of the WeedSmart Big 6 tactics except harvest weed seed control. With their focus on multiple in-crop strategies to minimise weed germination and seed set they find that their crops are almost weed-free at harvest.