Farm hygiene cottons on
The release of a range of Roundup Ready (RR) crops in the USA has generated wide-spread resistance to glyphosate across their main cropping zone where RR cotton, maize and soybean were routinely grown without any other weed control tactics implemented.
This is a scenario that St George farmer and cotton industry leader, Cleave Rogan, does not want to see repeated in Australia. He believes that the cotton industry must lead the way in Australia in managing glyphosate use across the rotation.
“Roundup Ready technology is a great tool for controlling weeds and in Australia we have RR cotton and RR canola, but unlike in the USA, these RR crops are seldom grown in the same paddocks. However, we do have a long history of relying on glyphosate in the fallow,” he says. “In the 20 plus years that we have grown RR cotton in Australia there has definitely been a shift in the weed spectrum on our farms, in favour of species that are tolerant of this mode of action.”
Prior to the introduction of Roundup Ready cotton varieties, bladder ketmia was the dominant weed on the Rogan’s 425 ha irrigated farm, ‘Bookamerrie’, in the St George Channel Irrigation System. Now feathertop Rhodes grass is the main weed of concern, along with fleabane and vines; a weed spectrum now dominated by species that have a natural tolerance for glyphosate.
Cleave and Johnelle purchased Bookamerrie in the mid 2000s and Cleave implemented an integrated weed management plan since day 1, with an emphasis on beginning every cropping season with very clean paddocks.
“The wider spectrum of weed species makes control more challenging and requires an on-going effort to maintain a high level of farm hygiene,” says Cleave. “We keep glyphosate for in-crop weed control only and generally use Spray.Seed (paraquat + diquat) to provide broad spectrum knockdown of weeds in non-crop areas and fallow.”
In-crop they use inter-row cultivation when the crop is small and apply a residual lay-by herbicide before the crop canopy closes over the row. “With the introduction of Roundup Ready technology we decided to continue the practice of a lay-by herbicide application however we have dropped out a pre-planting application of residual chemistry. Starting crops off in very clean paddocks has always been our priority.”
Cultivation plays an important role in weed management between crops, starting with ripping and side-busting to 100 mm or more after the cotton is harvested. This plays a dual role in managing weeds and disrupting the lifecycle of the heliothus moths. This is followed with bed-formation, fertiliser application and seed bed preparation — providing up to three cultivations between harvest and planting. In a wet winter, weeds typically germinate in late winter or early spring and may necessitate an additional cultivation prior to bed preparation. Although the introduction of Bollgard 3 comes with a reduced requirement for pupae busting, Cleave plans to continue using the tactic as a way to control herbicide resistance risk.
“We are modifying our cultivation practice to help conserve soil moisture. The 680 mm overlapping Versa Sweeps only cultivate the top 20 to 30 mm, which gives good weed control without drying out the topsoil. It also maintains the bed shape required for furrow irrigation,” he says. “This implement gives us a choice between chemical and mechanical tactics at planting, allowing us to respond to either weed pressure or bed maintenance needs of the paddock.”
“Having this extra flexibility means we can rip and fertilise, then leave the paddock to conserve moisture before doing a final preparation for planting. The amount of trash in the paddock also plays a part in this decision, whether we need to cultivate to incorporate the trash.”
“Bio-technology, including RR, has delivered improvements in cotton yield and quality every three to four years,” he says. “Each new variety also gives growers more flexibility in their farming system. In the early varieties, herbicide could only be applied when the crop was very small but more recent varieties allow applications of glyphosate at any stage of the crop, right up to 22 nodes.”
Cleave says the majority of their weeds arrive on farm in either irrigation or flood water. “Weeds will appear first in channels and head-ditches,” he says. “Once the crop is picked and the modules delivered we start on the residual herbicide program for the roads, channels and dams. This must be complete by the end of June to allow good incorporation by winter rainfall.”
There are a limited number of registered herbicide options available but Cleave rotates modes of action (MOA) as much as possible, basing herbicide choice on the likely weed species present.
Cleave has installed an automatic weather station at the homestead that collects data on wind, temperature and humidity to calculate Delta-T based on local conditions. This information is presented in a visual format that allows the spray rig operator to monitor the trend in Delta-T and to change nozzles or stop spraying when conditions change.
“The visual representation of the data on mobile devices means the operator can decide whether to stop spraying, re-fill or just finish the tank,” he says.
Cleave’s IWM program in cotton
- Start clean
- Spray glyphosate at crop emergence
- Light inter-row cultivation
- Spray glyphosate at 6 nodes crop stage
- Cultivate and apply lay-by (residual) herbicide
- If necessary, apply glyphosate at 16 node stage to control late emergence weeds
- Crop closure — irrigation as required
- Defoliation of crop (no impact on weeds)
- Mulch and root cut cotton
- Ripping for pupae busting
- Cultivation for bedforming and seedbed preparation
Cropping program at Bookamerrie
The Rogans are primarily cotton growers, with corn, sorghum, mungbeans, chickpea and wheat grown when seasonal conditions and water availability allows. All crops receive some irrigation and the aim is to produce high yielding, high quality crops that justify the use of irrigation.
If sufficient rain falls in autumn Cleave generally looks at chickpea as a good rotational crop for cotton. With this in mind he pre-fertilises some paddocks and leaves others for chickpea in the hope that adequate rain will fall. In some unusual years, like 2016, the chickpea crop can be grown without any irrigation.
“Each July we determine the base area that will go to cotton that year and we apply fertiliser to these paddocks,” he says. “If for any reason we don’t plant cotton in these paddocks, then we would plant sorghum or corn to use the fertiliser or leave the paddock until the next cotton season.”
“As the water availability becomes known we can increase the area sown to cotton right up to the end of our planting window in mid to late-November.”
Cleave’s farming system is based on 1 m crop rows, 2 m tractor wheel tracks, 8 m wide planter and implements and a 24 m sprayer.
Avoiding the USA experience with glyphosate resistance
Cleave Rogan is a strong supporter of IWM to protect the Roundup Ready technology, which is now the basis of the Australian cotton industry.
Having seen the effect of glyphosate resistance on cotton systems in the USA when he toured farms in 2014, Cleave says growers need to be continually looking for other ways to disrupt weed growth and seed set. He says chipping out survivor weeds along roadsides, in channels and head-ditches needs to be part of every-day management, along with putting in practice ‘come-clean, go-clean’ protocols.
“The one big mistake that growers in the USA made was to use glyphosate as their primary weed management tool in cotton and other crops as well as their fallow and non-crop areas,” he says. “Australian growers must take notice of this experience or we will face the same challenges. Dryland cotton and grain systems are most susceptible but it is also happening in irrigated systems.”
When deciding on opportunity crops Cleave takes weed management and the use of different modes of action into account in both summer and winter cropping seasons. This is in keeping with the cotton industry’s Roundup-Ready stewardship recommendation of ‘2 + 2 and 0’ of two non-glyphosate control tactics both in-crop and in fallow, and a zero tolerance of survivors.
“Feathertop Rhodes grass is a serious challenge for us,” he says. “We have had samples tested for glyphosate resistance, and at this stage the population remains susceptible but keeping it that way will rely on us maintaining a program that targets this weed when it is small.”