Read time: 3 minutes

Choose highly competitive canola

Canola has been making positive impacts on farm profitability over recent years but the cost of weed management has also been climbing. The availability of a wide range of herbicide resistant canola varieties, including triazine-tolerant (TT), Roundup Ready (RR), Clearfield® Production System (imidazolinone-tolerant) and dual RR–TT, has not kept a lid on weed management costs.

A strongly competitive canola crop can suppress weed biomass at flowering by a huge 50 per cent, significantly reducing the amount of weed seed added to the seed bank.

A strongly competitive canola crop can suppress weed biomass at flowering by a huge 50 per cent, significantly reducing the amount of weed seed added to the seed bank.

The challenge is to find out which canola varieties are able to out-compete weeds and so reduce the reliance on herbicides, and retard the spread of resistance. Researchers at the Graham Centre for Agricultural Innovation at Charles Sturt University and NSW DPI in Wagga Wagga have focused on this task, comparing the competitive ability of canola varieties against weeds.

Lead researcher Professor Deirdre Lemerle said the Australian-first study looked at the competitive ability of 16 canola genotypes against annual ryegrass and volunteer wheat over two contrasting seasons, without using herbicides.

“When a crop plays a central role in its own weed management there can be many great benefits,” said Professor Lemerle. “Sowing the most competitive variety can reduce herbicide dependence and costs without any yield penalty. This is an important non-chemical tactic to use against herbicide resistant weeds.”

The study showed a wide variation in the ability of current canola varieties to compete in the presence of weeds. Under the same weed pressure some varieties experienced a 50 per cent yield loss while others did not lose any yield.

“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,” she said. “As expected, the suppression of weed growth was strongly tied to crop biomass and early crop vigour. AV-Garnet, hybrid Hyola-50, and the Clearfield hybrids, Hyola-571CL, 45Y77 and 46Y78, were higher yielding and more competitive than the triazine-tolerant cultivars. Although the ranking of the 16 genotypes was influenced by seasonal conditions these genotypes were consistently more competitive than others.”

Speedy emergence, early vigour, rapid ground cover and height are all important characteristics of competitive crops, as varieties with these traits can rapidly ‘own’ the space in the field and ultimately squeeze out the weeds.

Other competitive traits can include sufficient large, thin leaves to effectively shade weeds, sufficient pod height to over-top neighbouring weeds (without unduly lowering harvest index), combined photosynthetic area (leaves and pods) sufficient to shade weeds at all stages of the growth cycle, high allelopathy and a rapidly established root system to uptake nutrients (N, P, K) and water.

Dr David Luckett, Senior research scientist at CSU examines the competitive ability of different canola varieties.

Dr David Luckett, Senior research scientist at CSU examines the competitive ability of different canola varieties.

“These traits also support high yield, so generally, genotypes that are high yielding—both in grain and oil content—in monoculture are also high yielding in the presence of weeds,” said Professor Lemerle. “When canola plants are losing the battle with weeds they are smaller and have less leaves than when they are growing in a weed-free environment. They are likely more attractive to insect and mouse attack.”

Another interesting but more difficult to study trait is the production of allelopathic chemicals that can suppress the growth of other nearby plants, including weeds. Canola is known to produce allelopathic chemicals that can suppress annual ryegrass root systems and the CSU team is leading the way in identifying the chemicals involved and finding the associated genetic markers.

“In the longer term we expect to be able to provide canola breeders with the information required to maximise the ability of canola crops to interfere with weed growth in the farming system through strong crop competition and allelopathic interaction,” said Professor Lemerle.

Related Articles

View all
Article
News

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.  
Article
News

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.
Article
News

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

Subscribe to the WeedSmart Newsletter