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Hybrid canola out-competes weeds

Canola production is predicted to rise by 30 per cent in 2017 with over 98 per cent of farmers growing herbicide-tolerant canola cultivars. However, Australia has been lagging behind other producing countries in the uptake of hybrid cultivars that offer higher yield and more options for effective weed suppression in crop rotations.

Researchers at Charles Sturt University compared the competitive ability of 16 genotypes – hybrid and open-pollinated cultivars – and found the most competitive cultivars reduced weed biomass at flowering by a huge 50 per cent, significantly reducing the amount of weed seed added to the seed bank. A similar trial, conducted by researchers at the University of Adelaide, found that annual ryegrass plants that survived pre-emergent herbicide produced more than twice as much seed in open-pollinated TT canola than in the hybrid Clearfield canola.

Although the triazine-tolerance (TT) trait is known to confer a yield penalty of up to 10–20 per cent, this technology is currently adopted on 65–70 per cent of the national canola area. The vast majority of TT canola cultivars are open-pollinated while most Clearfield (CL) and Roundup-Ready (RR) cultivars are hybrids.

Kevin Morthorpe, *GenTech Seeds’ Canola Business Lead and Product Stewardship Manager hopes that the new hybrids available in 2017 will encourage growers to continue to shift away from the less competitive, open-pollinated cultivars to take advantage of the more vigorous, higher biomass and higher yielding hybrids.

Kevin Morthorpe, GenTech Seeds, is concerned that canola growers are relying too heavily on the less competitive triazine-tolerant (TT) cultivars and missing out on the higher yield and better weed control benefits of hybrid canola systems.

Kevin Morthorpe, GenTech Seeds, is concerned that canola growers are relying too heavily on the less competitive triazine-tolerant (TT) cultivars and missing out on the higher yield and better weed control benefits of hybrid canola systems.

“Crop competition is one of the best non-herbicide weed management tools available and the new hybrids are offering growers real bang for their buck in terms of extra yield and driving down the weed seed bank,” he said. “These benefits for the grower far out-weigh the additional cost of hybrid canola seed. The yield advantage achieved through hybrid vigour only occurs in the F1 generation so retaining seed for future use is counter-productive.”

Mr Morthorpe said enhanced crop competitiveness in hybrid crops is best achieved through attention to crop nutrition to optimise early growth and harvestable yield. “Research studies in canola have not shown a plateauing in crop yield response to higher nutrient input as is often observed in the ‘haying off’ of cereals at higher nutrient rates,” he said.

The suppression of weed growth is closely tied to strong root development, increased crop biomass and improved early crop vigour. Field trails also indicate that some cultivars have an allelopathetic effect on weeds. Speedy emergence, early vigour, rapid ground cover and height are all important characteristics of the most competitive hybrids.

Hybrid growers are also able to strategically integrate alternate herbicide modes of action and reduce reliance on Group A herbicide applications in the canola phase.

Hybrid canola suppresses weed biomass and seed production by about 50 percent compared to open-pollinated triazine-tolerant (TT) canola cultivars due to the speedy emergence, early vigour, rapid ground cover and height characteristics of the most competitive hybrids.

Hybrid canola suppresses weed biomass and seed production by about 50 percent compared to open-pollinated triazine-tolerant (TT) canola cultivars due to the speedy emergence, early vigour, rapid ground cover and height characteristics of the most competitive hybrids.

Herbicide Tolerant Canola Stewardship Guide

GenTech Seeds, an industry partner of WeedSmart, is committed to product stewardship. Their recently-published ‘Herbicide Tolerant Canola Stewardship Guide’ outlines the sustainable use pattern for all herbicide tolerant cultivars. Mr Morthorpe said the stewardship guide is a practical approach to integrated weed management within the canola phase and fully supports the The Big 6.

“In triazine-tolerant crops the main points are to carefully manage the lower crop vigour of TT canola, monitor triazine herbicide carryover risk for crop rotational planning and always adhere to mandatory application practices for triazine herbicides (atrazine, simazine) set by industry in cooperation with government,” he said.

“To protect Clearfield technology, the whole farm rotation plan needs to limit the use of ALS-inhibiting herbicides to no more than two out of four years. Avoid crop injury by using quality assured, first generation seed and monitor the carry over risk of imidazoline herbicide on future crop rotation options.”

“Planting Roundup-Ready hybrids requires a critical assessment of the use of glyphosate as a stand-alone knockdown for non-crop application such as fencelines and over-reliance across the farming system. A whole-farm strategy needs to be in place to manage glyphosate resistant weed populations and to control RR crop volunteers in the fallow phase.”

The general principles for weed control and herbicide use apply for all herbicide tolerant canola systems, including using a combination of registered pre-emergent and post-emergent herbicides, always following the label directions of use and pro-actively implementing diverse weed management tactics across the farming system.

Post-emergent herbicide applications must target small weeds (2–3 leaf ryegrass and/or 2–3 cm diameter broadleaf leaves) early in the crop’s development and selective herbicide application should occur before elongation of canola plants (BBCH 16).

“When it comes to managing herbicide resistance and protecting the plant breeding technologies available, the key is to have low weed numbers entering and leaving the canola phase,” he said. “To achieve this, growers can rotate the crop types, herbicide tolerance technologies and herbicide modes of action used across the crop rotation to broad the opportunities to implement a diverse range of weed management tactics to prevent weed seed set and to implement harvest weed seed control to collect any seed present at harvest.”

The ‘Herbicide Tolerant Canola Stewardship Guide’ includes a detailed integrated weed management (IWM) strategy that highlights herbicide and non-herbicide tactics growers can employ in the pre-planting, in-crop, harvest and post-harvest phases to control weeds and reduce weed seed set.

This Guide also promotes recommended stewardship practices along the supply chain to ensure responsible use of new technologies, predictable market access and builds on Australia’s competitive edge in international oilseed markets.

*GenTech Seeds is the exclusive producer distributor of Pioneer® brand products in Australia.

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Never cut the herbicide application rate

Scientific studies have demonstrated that resistance can rapidly evolve in weeds subjected to low doses of herbicide. Some weeds can develop resistance within a few generations. Full rates when mixing herbicides too! When mixing herbicides it is important that each product is still applied at the full label rate to ensure high mortality. Applying different chemicals in one mix can provide an additive advantage. It is important to understand the mode of action of each herbicide on the plant when preparing a herbicide mix. This is just as important for pre-emergent grass weed mixes as it is for post-emergent mixes aimed at broadleaf weed control. ALWAYS READ THE LABEL. Surrounding weed seeds with a combination of pre-emergent herbicides with different modes of action can give a high level of control and help extend the useful life of all the chemicals used. The high level of control must be supported with additional control measures for all survivors. All products with different modes of action must be applied at full label rates for this to be an effective strategy.   Mixing two chemicals with the same mode of action can achieve some additional efficacy, however, the mix should deliver the combined full rate to ensure a lethal dose. The amount of stubble present and crop safety are all important considerations when mixing chemicals. For example, when using a tank mix of Avadex® and trifluralin to control ryegrass in wheat, the rates used will vary depending on the sowing system and level of stubble retention. Be sure to get good advice. Many herbicides on the market are a combination of two or more modes of action within the one product. These products must be applied at the full label rate to be effective. Having dual action does not negate the need to change herbicide products and rotate modes of action. Repeated use of any single strategy will reduce the effectiveness of that strategy over time.  

Spray well – correct nozzles, adjuvants and water rates

Spray application is a technical field and growers need to make sure their equipment and application techniques are spot-on. The GRDC Spray Application GrowNote provides detailed information and about 80 videos to demonstrate key skills. Prevent spray-drift The focus of spraying herbicide needs to be on doing the job right so the weeds receive the correct dose and die, and this includes reducing the air borne fraction to a bare minimum. Bill Gordon’s 10 Tips for Reducing Spray Drift Choose all products in the tank mix carefully. Understand the product mode of action and coverage requirements. Select (and check) the coarsest spray quality that will provide effective control. Expect that surface temperature inversions will form as sunset approaches and will likely persist overnight and even beyond sunrise on many occasions. DO NOT SPRAY. Use weather forecasts to inform your spray decisions. Only start spraying when the sun is about 20 degrees above the horizon and when the wind speed has been above 4–5 km/hr for more than 20–30 minutes, and clearly blowing away from any adjacent sensitive crops or areas. Set the boom height to achieve a double overlap of the spray patterns. Avoid higher spraying speeds. Leave buffers unsprayed if necessary and come back. Continue to monitor conditions, particularly wind speed, at the site during the spray operation High water rates don’t have to slow you down Some growers are concerned that increasing the water rate when applying herbicide will slow down their spray operation and cost them money. However, the biggest financial loss during spraying usually comes from a failed spray job. To keep your spray operation as time efficient as possible when using more effective and reliable application volumes, you can: Use nurse tanks around the farm to reduce the time spent travelling back to a central re-fill point. Use a larger pump, e.g. 2.5 inch, to make re-filling quicker. Pre-mix the batch while the sprayer is operating. Many mixes can be held in the mixing tank for up to 6 hours. However, wettable granules and suspension concentrates will need agitation to keep them in solution. For pre-emergent herbicides in high stubble situations, carrier volume has a large effect on the level of control achieved. Across four trial sites Dr Borger’s research demonstrated that ryegrass control with trifluralin or Sakura® increased from 53% control when the carrier volume was 30 L/ha to 78% control when the carrier volume was increased to 150 L water/ha in high Water quality and mixing order Water quality is often overlooked as a possible contributor to herbicide failure and can lead to confusion over the herbicide resistance status of weeds on a property. Water should be considered as one of the chemicals in any mix, given that water quality varies markedly depending on its source. Getting the mixing order right is essential for effective spray results. Don’t start mixing until the water quality is right Podcast – Mixing herbicides Adjuvants Sometimes adding an adjuvant is beneficial and sometimes it is detrimental; and there is an art to knowing how to best deploy these additives. When weeds are susceptible to the applied herbicides, the effectiveness of adjuvants generally goes un-noticed. Correctly applied adjuvants can reduce the impact of low level herbicide resistance by helping to maximise the amount of herbicide taken up by the plant.

Clean borders – avoid evolving resistance on the fence line

About one-quarter of glyphosate-resistant populations within broadacre cropping situations across Australia come from fencelines and other non-cropping areas of the farm. Along paddock borders, where there is no crop competition, weeds can flourish and, if not controlled, set lots of seed. The traditional approach has been to treat these weeds with glyphosate to keep borders clean but after 20-odd years this option is now failing and paddock borders are becoming a significant source of glyphosate-resistant weed seed. Weed researcher Eric Koetz said the limited options for managing weeds along irrigation infrastructure and other non-crop areas is a problem and is putting additional pressure on knock-down herbicides in irrigated systems. In some situations, cultivation can be used to kill the weeds and provide a firebreak, but on light soils this may pose an erosion risk and mowing or slashing may be safer options. Another possible tactic is to continue using herbicides but to ensure that a clean-up operation is carried out before any survivors can set seed. Some growers are choosing to increase the heat on weeds along the borders by planting the crop right to the fence and then baling the outside lap and spraying with a knockdown herbicide to kill any weeds and provide a firebreak. Another good option in some situations is to maintain a healthy border of vegetation using non-invasive grasses. In Queensland, buffel grass is a good example of a grass that can outcompete other weeds while not invading crop lands. If only herbicides are used on fencelines, resistance is inevitable. Surviving weeds on fencelines have no competition and access to plenty of soil moisture, so they set a lot of seed and resistance can easily flow into neighbouring paddocks. Other resources It’s time for a glyphosate intervention Farm hygiene cottons on – Cleave Rogan, St George What’s new in management of herbicide resistant weeds on fencelines? Keeping the farm clean – Graham Clapham, Norwin Don’t jeopardise glyphosate for clean fencelines Keeping fencelines clean Resistance risk to knock-down herbicides on irrigated cotton farms

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