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Success in tackling weeds

With the harvester back in the shed and seeding around the corner, it’s the time of year when summer spray regimes are front of mind.

Rising chemical costs, greater summer rainfall and the increasing incidence of herbicide resistance mean summer spraying is serious business.

Gnowangerup farmer Knud Nymann is using every trick in the book to attack weeds, and a combined control approach is helping him reduce his summer weed burden.

Maintaining livestock in his operation as well as the recent incorporation of chaff carts and light cultivation methods play an important role in weed control on his 12,000 hectare property which spans the Great Southern region from Gnowangerup to Wellstead.

But for Knud, it was a targeted approach to spray application that not only led to considerable cost savings and reduced environmental impact, but has proven to be the most effective method for successful weed knockdown.

Since introducing Weedit spray technology three years ago, Knud said he had saved up to 90 per cent in herbicide costs.

The technology actively detects live plant matter, only applying chemical when a target plant is detected rather than the blanket fence-to-fence application method used in conventional systems.

Knud started with a 24-metre, hired Weedit unit in 2011, and today uses a 36m unit which is a key tool in his summer spraying toolbox.

“The cost savings are pretty straight forward because if you spray 1000ha and you use a brew that cost $20-$25 and you only spray 10pc – say 100ha out of the 1000ha – then you saved yourself a fair bit of money because it only cost you $2500 in chemicals when it would have cost you $25,000,” Knud said.

“The strike rate will vary from job to job and the year.

“At home this year the weed percentage was only 6pc, so if you work on 10pc chemical use you save 90pc.”

With a cropping program of 11,000ha, Knud said it was easier to justify the expenditure in a bigger operation because although the technology was expensive the potential savings were greater.

“The machine pays itself off relatively quickly but obviously the more weeds you have the slower it pays off,” he said.

Courtesy Farm Weekly

Courtesy Farm Weekly

Knud said he had noted herbicide resistance issues on-farm, particularly glyphosate resistance in Fleabane and Windmill Grass, and although the cost of older existing chemicals hadn’t increased greatly, he had found he needed to use more to achieve comparable results, which meant the cost per hectare of spraying had increased.

“We used to use 150ml of Select to kill ryegrass immediately and now we use half a litre instead,” he said.

“The good thing about the Weedit is you could start using newer, more expensive chemicals, because you are only using so little of them.”

In addition to cost savings, Knud said targeted chemical application had environmental advantages.

“With target application, the environment is obviously not exposed to all these chemicals that are sprayed out on the bare dirt for nothing,” he said.

“You are only striking when there is something to strike for.”

Although pleased with the system, Knud had a few words of caution for those looking to utilise detector spray systems.

“Don’t skip rates when using detector spraying systems, go hard,” he said.

“And conditions are still king, if we do go into warm conditions a spray oil for prep purposes is an absolute must.”

Knud said significant rain on his Wellstead property meant he could only spray a quarter of the program with the Weedit this summer because weed percentages were too high for the process to be viable.

“With strike rate success on Fleabane, depending on size and what brew you use, don’t expect to be getting two thirds or three quarters,” he said.

“Fleabane seems to be extremely hardy.

“We are actually going back to the old double knock in the summer weed context for Fleabane.

“If you have an 80pc strike rate, the last 20pc is still there and it’s a worry.

“We did some spraying with the Weedit, about 1100ha but some of the percentages were too high so we actually sprayed them fence-to-fence.

“We will see if the fence-to-fence was a lethal dose, because it gets pretty expensive with Fleabane.

“And then we’ll go back over it with the Weedit.”

Mr Nymann said he also dabbled in light cultivation, using discs as a way to vary the method of controlling the weed burden.

“You can’t do too much of the same thing,” Mr Nymann said.

“Cultivation is also incorporating the stubble into the dirt.

“It is a misconception that the stubble should stay up in the air – it should be down where all the microbes are.”

Mr Nymann said he had also invested in chaff carts as another tool in combating weed issues and they were largely used on the Wellstead property.

“A chaff cart is a fair bit of outlay so we decided to drop windrows this year just to see how that goes,” he said.

Mr Nymann said chaff carts worked in well with his livestock and weed control program.

“We generally run 350 black breeder cattle in Wellstead, and mate 2800 Dohne ewes,” he said.

“Even when you go in with a detector sprayer, having livestock in the mix is always beneficial.”

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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

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