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Early identification allows more effective weed control

Weed identification is a valuable skill and most farmers can identify the common and important weeds on their farms. For most non-botanists, identification is easiest when the plant is mature and flowering – but to be effective, weed control decisions need to be made well before flowering.

With the increasing prevalence of herbicide resistance across all farming regions, accurate identification at early growth stages is essential to ensure the best control strategies are implemented when the weeds are at their most susceptible growth stage.

Using just the cotyledon shape as the only diagnostic selection, the 50 possible species can be rapidly narrowed down to less than eight possibilities in most cases. Early identification gives growers the opportunity to apply the best weed control program to treat the species present.

Dr David Thornby, Innokas Intellectual Services says the resistance profiles, even for closely related species, can be quite different, especially at the seedling stage.

“As part of a Cotton Research and Development Corporation project we have developed a new weed identification mobile app called ‘Weeds of Australian Cotton’ that provides a key to the characteristics of 50 weed species in cotton,” he says. “Clearly, the app will also have value for use in managing weeds in other crops grown in the same regions as cotton.”

The app allows users to make selections based on the observed characteristics of the plant, stem, leaves, flowers and seeds, the fleshiness or succulence of the plant and the presence of milky sap or latex. For grasses, users can key in specific details about the inflorescence, spikelet, floret and ligule features. As each detail is added the number of possible species reduces, until a few or just one remains as the best fit for the characteristics selected.

“Once there are just a few remaining options, the user can look at the photo gallery and choose the best-fit identification,” says Dr Thornby.

“The feature that really sets this app apart from other weed identification apps is that ‘Weeds of Australian Cotton’ includes a ‘cotyledon shape’ characteristic selection.”

“There are nine different cotyledon shapes to choose from. Using this feature of the app alone, users can quickly narrow down the most likely identification, and make decisions early regarding the best mix of weed control strategies to implement.”

Using the cotyledon shape as the only diagnostic selection, the 50 possible species can be rapidly narrowed down to less than eight possibilities in most cases. When cotyledons are present on very small plants found in the field, accurate identification can give growers a head start on planning a spray application.

The timing of herbicide application is product-specific but the general recommendation is for weeds to be ‘small and actively growing’. As a rule of thumb, ‘small’ would include pre-tillering for most grass species, less than 5 cm diameter for most rosette-forming species, and up to about 5 true leaves for other types of broadleaf species. As for ‘actively growing’, this is simply the absence of visible signs of moisture stress.

“Coverage is probably the most important factor to consider if weeds were sprayed at cotyledon stage,” says Dr Thornby. “Where feasible, increasing the water rate is the usual response, but it can be hard to hit such genuinely small targets. At this very small size good control could be expected, but they would have to come in contact with the chemical and so it is often practical to compromise by waiting until a couple of true leaves are present.”

“It is essential that label instructions are followed regarding weed size, product rate and application method as they apply to each product and weed species to achieve the best weed control result.”

It is best not to make too many assumptions about the weed spectrum present based on what was observed in the previous year. Dr Thornby emphasises the need for accurate identification and highlighted the fact that the app does not include every possible plant that could be growing on a cotton farm.

A new weed identification mobile app called ‘Weeds of Australian Cotton’ provides a key to the characteristics of 50 weed species in cotton. The app will also have value for use in managing weeds in other crops grown in the same regions as cotton.

“The app only includes the 50 species that the development team identified as the key species affecting cotton production,” he says. “Misidentification is certainly possible, so if the options remaining at the end of your selections do not clearly match the plant you are looking at in the field, it is necessary to confirm identification with an expert, especially if the weed is proving hard to kill.”

Download ‘Weeds of Australian Cotton’ app on the Apple App Store for iOS mobile devices or Google Play for Android mobile devices or visit www.cottoninfo.com.au

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WeedSmart agronomist set to tackle high rainfall zone weeds

Every locality has its own spectrum of weeds, and growers face different opportunities and challenges regarding the control tactics they can employ.
The WeedSmart Big 6 approach is a practical way to ensure that an integrated weed management program is put in place that disrupts weed seed production and the evolution of herbicide resistance.
Commencing in January 2021, Jana Dixon has joined the WeedSmart team of extension agronomists, with a focus on applying the Big 6 to manage weeds in the high rainfall cropping systems of southern Australia – from Esperance in WA to south-eastern SA, Tasmania and south-western Victoria.
Jana will add to the dedicated and experienced extension agronomists on the WeedSmart team with Peter Newman in the Western region, Chris Davey in the South, Greg and Kirrily Condon in the East and Paul McIntosh in the North.
Jana Dixon has joined the WeedSmart team of extension agronomists, with a focus on applying the Big 6 to manage weeds in the high rainfall cropping systems of southern Australia – from Esperance in WA to south-eastern SA, Tasmania and south-western Victoria.
Jana hails from the Mid North of SA, and began working at Pinion Advisory (previously Rural Directions) while she was studying agriculture at the University of Adelaide. She has been employed full-time at Pinion Advisory since January 2019 as an agribusiness consultant, based in Clare, and spends most of her time delivering agronomy and farm business advice to clients from a wide range of cropping regions in South Australia.
Pinion Advisory is a foundation WeedSmart sponsor and Jana has been involved in two WeedSmart Week events already – the first as a participant and grower group organiser at the Horsham event in 2019 and then as the local organiser for WeedSmart Week 2020 in Clare.
In welcoming her to the WeedSmart team, program manager Lisa Mayer says Jana brings energy, commitment and insight to deliver communications focussed on the southern region’s high rainfall regions.
“Growers in the southern high rainfall zones are facing some serious issues with herbicide resistance influencing their farming decisions,” says Ms Mayer. “Jana will be engaging with agronomists, growers and researchers in each of the distinct high rainfall zones to understand the complexities and look for practical ways to apply the WeedSmart Big 6 in various cropping scenarios.”
“We plan to deliver WeedSmart Week in Esperance, part of Western Australia’s high rainfall cropping zone, in August 2021 and Jana will play a key role in the planning and delivering of our annual 3-day flagship event.”
Jana says her experience with the WeedSmart program has been very positive and she has been particularly impressed with the support the program has from all sectors of the grains industry.
Newly appointed WeedSmart extension agronomist, Jana Dixon (green cap) leading discussions with farm visit host, Ben Marshman, Owen SA, and growers and agronomists attending WeedSmart Week 2020 in Clare.
“I have spoken to many growers and agronomists who have found real value in the information that the WeedSmart program delivers,” she says. “For many it is as much about considering another operator’s philosophy on dealing with weeds, and taking a fresh look at their own systems, rather than just learning about a new tactic or the traits of a new herbicide in isolation from the big picture.”
She says the high calibre of industry people who contribute their time and expertise to the program is testament to the value WeedSmart has to agribusiness, growers, agronomists and researchers alike.
In taking on the responsibility for delivering information tailored for the high rainfall zones Jana says she is pleased to have an extensive network of contacts through Pinion Advisory, with offices in a number of high rainfall areas to provide easy access to local agronomists and growers. She is also aware that there are major differences in weed spectrums and farming systems in each high rainfall zone and plans to take full advantage of the opportunity this role presents to expand her understanding of different approaches to weed management.
“The long and favourable growing season and the associated prolonged periods of weed germination, is a key factor that I see potentially impacting on a grower’s weed management strategies in these regions,” she says. “On the other hand, access to highly diverse rotations and a focus on crop competition are two strategies that can play an important role in achieving excellent weed management in these regions.”
“I am keen to engage with anyone working and farming in the high rainfall zones to build my knowledge and understanding,” she says. “And to create opportunities to develop and extend the WeedSmart Big 6 strategies, both herbicide and non-herbicide, that work in each area and in different situations.”
WeedSmart is the industry voice delivering science-backed weed control solutions with support from the Grains Research and Development Corporation (GRDC), major herbicide, machinery and seed companies, and university and government research partners, all of whom have a stake in sustainable farming systems.
You an follow Jana on Twitter and keep up to date with the HRZ here.

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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.
 

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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.

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