Keeping a lid on weeds growing in your crops
In-crop weed control is particularly difficult in some years. Even after you have done all you possibly can to get your crop off to a competitive start the growing season can throw up some major challenges.
In this article we explore key principles that impact on the efficacy of in-crop ‘selective’ herbicides. You will most likely have to make some compromises and it is almost impossible to implement every tactic perfectly every time.
Herbicide mixes help to preserve the effectiveness of each mode of action by avoiding unnecessary usage.
Over the last few years WeedSmart has collected and promoted great advice from seasoned agronomists, wise researchers and crafty farmers on all aspects of weed control. To save you some time we have collected the resources that we think can be of assistance as you make the hard decisions about what to apply, when to apply and how to apply the herbicide and non-herbicide weed control tools at your disposal.
Post-emergent herbicides have been widely used in Australian crops because they are generally highly effective and easy to use. Unfortunately, their popularity has led to widespread resistance and most farms will have at least one weed species that is resistant to at least one post-emergent herbicide mode of action.
Despite recent increases in resistance, post-emergent herbicides remain an integral component of weed control strategies in many production systems.
Avoid the routine use of any weed control tactic – mix, rotate and keep changing.
Know what modes of action still work – test for susceptibility.
Have a plan for dealing with a weed blow-out.
Right Product, Right Time, Right Application.
Planning your in-crop herbicide use
Widespread and increasing herbicide resistance demands a planned approach to herbicide use throughout the crop sequence. If you have been using a particular herbicide or group of herbicides routinely, it is probably because they work well. To ensure these effective products remain an option into the future, it is necessary to use them less often!
Testing weeds for their susceptibility to a range of herbicides is cheap compared to applying a herbicide that has limited or no effect. Resistance to one or more herbicide does not mean you have no options.
We now know that mixing and rotating herbicides is an effective strategy to prolong the effective life of each mode of action. But even these mixes and rotations need to be change.
There are currently very few in-crop herbicides available for grass control. There are more options for broadleaf control. Plan a herbicide use program that spans your crop sequence so you can ‘save’ particular herbicides for use in crops where there might be limited alternatives, while using a range of other modes of action in other crops.
All herbicides applied in crop will have some impact on crop safety. Herbicides must be applied according to the correct crop growth stage for each herbicide.
Shielded spraying opens up the possibility of using other chemistry in-crop that would otherwise not be an option. Some growers are also looking for ways to include non-herbicide in-crop tactics such as inter-row cultivation or scuffling in wider-row cropping situations.<
CLICK IMAGE TO DOWNLOAD FILE
For planning herbicide use through the season and the crop sequence the NSW DPI Weed Control in Winter Crops booklet is full of useful tables of selective herbicides for each crop type. Click to download a copy.
CLICK IMAGE TO DOWNLOAD FILE
If you don’t have a copy of Mark Congreve and John Cameron’s ‘Understanding Post-emergent Herbicide Weed Control in Australian Farming Systems’ GRDC technical manual, you really need to download this resource.
CLICK IMAGE TO DOWNLOAD FILE
The GRDC Integrated Weed Management in Australian Cropping Systems manual provides a comprehensive guide to IWM, including the use of in-crop herbicides.
CLICK IMAGE TO DOWNLOAD FILE
This table shows the in-crop herbicides and their application timing for cereals. It is an extract from the NSW DPI Weed Control in Winter Crops booklet. You can download a copy here.
What are the ‘mix and rotate’ options for in-crop herbicides?
Testing for susceptibility and resistance
How can I implement the mix and rotate strategy to combat herbicide resistance?
How can I avoid getting stuck in an imi herbicide cycle?
Can we grow broadleaf crops without clethodim?
What can be done to regain control of herbicide resistant sowthistle?
Grower case study: Tim Rethus, Horsham Vic
Grower case study: Leigh Bryan, Swan Hill Vic
Grower case study: Phil and Brad Jackson, Westmar Qld
– Achieving maximum impact
Herbicide application decisions are complex and it is almost impossible to have all the important factors in place every time. Start with the product label and follow the instructions on rate, nozzle use, boom height, speed, adjuvants, optimal environmental conditions and so on.
When mixing, the order is important to avoid precipitation in the tank but it is also important to ensure that the tank mix partners each retain their efficacy. Some mixes are antagonistic and should be avoided because this will likely result in a significant reduction (up to 50% in some products) in efficacy. Adding an adjuvant can reduce herbicide selectivity and thereby increase crop damage.
The GRDC GrowNote Spray Application manual provides detailed information on:
Planning your spray operations – things to think about
Preparing for spraying – checks, accuracy and efficiency
Spraying system – major components and set-up considerations
Selecting a spraying system options available and operational considerations
Review and planning for future needs
CLICK IMAGE TO DOWNLOAD INTRODUCTION MODULE
The manual comprises 23 modules and a ‘water flush for residuals’ calculator. Each module includes a series of videos (see playlist below).
The video playlist is a great place to start:
Getting mixing right to avoid glugs and efficacy issues
Don’t start mixing until the water quality is right
Spray well: correct nozzles, adjuvants and water rates
Are you going spraying or killing weeds?
Never cut the rate
Right time – Manage multiple germinations
Timing is one of the hardest things to get right. Large spray programs and wet weather can make it very difficult to apply herbicides at the optimal time in every paddock for every weed.
The guiding principle is to always target small weeds, even if this means multiple applications. In wet years, multiple germinations will occur and waiting for the next germination invariably means the first flush will be much more difficult to kill and more likely to generate lots of seed for next year.
All herbicides applied in crop will have some impact on crop safety. Herbicides must be applied according to the correct crop growth stage for each herbicide. Also consider the effect of environmental conditions, particularly frost, on crop safety.
Environmental conditions at the time of spraying can make a huge difference to herbicide update in weeds. Look for the directions on the label for optimal conditions as spraying outside these parameters will result in less effective weed control.
avoiding chemical residues in grain.
Spray small multi-resistant radish twice
Does ambient temperature really affect herbicide performance?
Be ready for weed blow-outs
Wet years are the classic weed blow-out situation. Pre-emergent herbicides breakdown faster, spray applications can’t be applied on time and weeds will take advantage of any gaps that might develop in the crop.
Monitoring the weed pressure and having a plan to limit the potential damage might help.
The aim is to stop a massive seed set event using tactics such as – crop topping, hay or patching out. And be ready to implement harvest weed seed control – all the methods work well.
Grower case study: Trevor Syme, Bolgart WA
Grower case study: Mark Branson, Stockport SA
Grower case study: Day Family, Lockhart, NSW
Extent of herbicide resistance in summer weeds revealed
The first multi-species herbicide resistance survey conducted in the Northern grain growing regions of NSW and Queensland has shown that while resistance to key herbicides is prevalent, growers are keeping weed numbers low, for now.
Rising resistance to glyphosate has been clearly demonstrated but this key herbicide can continue to be a highly effective tool for weed control, provided growers and agronomists implement a variety of tactics, such as the double knock, mixing and rotating herbicides and seed bank management, as a matter of urgency.
Dr Adam Jalaludin (DAF) collecting weed seed to be screened for herbicide resistance in the first multi-species weed survey in the northern grains region.
With GRDC investment, Dr Adam Jalaludin, Department of Agriculture and Fisheries, Queensland and Dr John Broster, Charles Sturt University NSW led their respective teams through the process of testing samples and analysing the results for weed seed collected throughout the Northern cropping region in 2016 and 2017. This survey was part of a wider GRDC investment in ‘Innovation in Crop Weed Control’ project across the northern region.
Weed seed samples were collected from 440 paddocks across northern NSW (244) and Queensland (196). The seeds were sown in controlled conditions and when the plants reached the three to five leaf stage they were tested for resistance to a range of herbicides. While collecting weed seed samples the researchers also assessed the weed density in each surveyed paddock.
The summer weed species collected across the northern region and screened in Queensland included sowthistle, fleabane, awnless barnyard grass, feathertop Rhodes grass, windmill grass and liverseed grass.
Of these predominantly summer-active species, only sowthistle, awnless barnyard grass and liverseed grass are listed on the label as being controlled by glyphosate alone. There is no label claim that the other three species – fleabane, feathertop Rhodes grass and windmill grass, will be controlled at the registered label rates of glyphosate (729 g active ingredient per ha).
“Not surprisingly, all fleabane populations collected failed the glyphosate test,” says Dr Jalaludin. “Interestingly, 32 per cent of the feathertop Rhodes grass populations and 42 per cent of the windmill grass populations were actually susceptible to glyphosate.”
“Of concern was that 36 per cent of awnless barnyard grass populations and 14 per cent of the sowthistle populations were resistant to glyphosate.”
Dr Adam Jalaludin (DAF) recommends herbicide susceptibility testing as the first step in addressing patches of resistant weeds.
“In this survey we detected evolved resistance to haloxyfop in feathertop Rhodes grass and to imazapic in windmill grass, albeit at a low frequency.”
Glyphosate resistance is certainly entrenched in the northern region, and for sowthistle is much worse than in other areas of Australia. The good news is that weed density is relatively low and there is susceptibility to other herbicides.
“It is essential that an integrated approach is taken to manage these key weeds in summer crops and fallow,” said Dr Jalaludin. “An increasing number of weeds from a range of species are surviving glyphosate treatment, giving a clear indication that over-reliance on this herbicide is unsustainable.”
“Herbicide testing is a good place to start to identify which herbicides provide the best control. Herbicide applications should be supported with as many other WeedSmart tactics as possible and any survivors removed.”
Summary of results
The populations of viable sowthistle seed were screened with glyphosate, 2,4-D amine, Velocity and chlorsulfuron. Glyphosate and cholsulfuron provided poor control while all populations were susceptible to 2,4-D amine and Velocity.
Fleabane populations 1 week after spraying with glyphosate. Susceptible control population (right) and a resistant population (left) collected during the northern region herbicide resistance survey.
Fleabane populations across the Northern region were screened with glyphosate and 2, 4-D amine. All fleabane populations tested survived treatment with glyphosate while no sample survived the application of 2,4-D amine.
Screening of the feathertop Rhodes grass populations revealed 68 per cent were not controlled by glyphosate. One population survived treatment with haloxyfop, while all populations were controlled with clethodim.
Thirty-six per cent of the awnless barnyard grass populations collected across the Northern region were resistant to glyphosate. Fortunately, all populations were susceptible to propaquizafop, clethodim and imazapic.
Most of the windmill grass populations sampled in the survey were found in NSW. Screening showed that more than half (58%) of the populations were not controlled with glyphosate. Similarly, 40 per cent of the populations survived imazapic treatment. All populations were totally controlled by propaquizafop and clethodim.
The screening of the few viable liverseed grass populations collected across the Northern region did not reveal any evolved herbicide resistance.
Weeds collected in this survey were screened against several herbicides for which there are no label claims for some species. In field conditions, these weeds are often subject to exposure to a range of herbicides, which may be observed to have some activity. It is illegal to apply herbicides in any way contrary to the label and the results from this research are not a recommendation of use.
Calculating the cost of HWSC for your farm
When it comes to harvest weed seed control methods there is good evidence that all the available options achieve a similar end result in terms of weed seed bank decline. But there is a wide variation in initial outlay, in associated activities and in nutrient removal or concentration.
Then there is the on-going problem of using average costs compared to using your own costs when doing the calculations.
WeedSmart western extension agronomist, Peter Newman has developed a spreadsheet growers can use to do calculations for their own farm to compare the cost of different HWSC options.
To assist, WeedSmart western extension agronomist Peter Newman has developed an interactive spreadsheet tool that growers and advisors can use to compare the costs of the available harvest weed seed control (HWSC) tools, using data and costings from their own farm situation.
“We have good data to suggest that harvest weed seed control costs are $7 to $19 per hectare and there are only minor differences in the cost between the available tools when compared using the same farm data,” says Peter. “But because every farm is different and small differences in costs per hectare can make a big difference at the whole farm scale, it is important for growers to have confidence that they can afford and justify the expenses incurred.”
Some HWSC tactics involve the purchase of substantial machinery – such as an impact mill, chaff cart or chaff deck – but the operational and labour costs might be lower than methods such as narrow windrow burning, which involves low set-up costs but higher nutrient losses and labour costs associated with burning. Invariably narrow windrow burning is the most expensive option in the long-run due to the high nutrient removal cost.
There is good data to suggest that harvest weed seed control costs are $7 to $19 per hectare and there are only minor differences in the cost between the available tools when compared using the same farm data. A chaff cart (pictured) is a particularly good fit on mixed farms.
“As a general rule, the cost of HWSC is lower per hectare on larger farms with lower yields,” says Peter. “This is because the capital cost is spread over a larger area, less nutrients are removed because the yields are lower and the low biomass crops allow low harvest heights without slowing down the harvester or using extra fuel. The converse is generally true for smaller farms with higher yields.”
“By imputing your own figures into the HWSC costing tool you can quickly evaluate the financial impact of the available options,” says Peter.
Another important factor to consider is that some of the technology is relatively new to market and there are unknowns such as the expected life of components when operating in commercial field conditions. As time goes by the manufacturers will be able to provide more concrete advice on service and repair costs, and any component failures will be overcome.
The easy-to-use spreadsheet takes into account capital cost, nutrient spread/loss, cost of ownership, harvest cost, reduction in harvest capacity, fuel use and replacement of wearing parts. Users also input data about their farm size and crop yields.
Peter Newman joined us for a webinar to discuss the HWSC cost estimate tool, you can watch the full recording below.
Interest in cover crops continues to grow
There is a growing interest in planting cover crops in cotton and broadacre systems, providing the potential to preserve soil moisture, improve soil health and manage weeds.
As part of the CRDC project ‘Staying ahead of weed evolution in changing cotton systems’, the Queensland DAF Weed Science team investigated the impact of cover crops on weed suppression.
Jamie Grant (far right) is pictured with Jeff Werth (DAF weeds researcher). Jamie grows French white millet as a cover crop in rotation with cotton in his dryland cropping system at Jimbour, on the Darling Downs.
Research has shown that cover crops can provide a benefit in terms of weed control. However, in order for them to be effective, it is important to start with a clean crop and ensure that the cover provided is adequate and evenly spread.
Similar to findings from grower Jamie Grant in the following case study, research showed that when the cover was not adequate, lower amounts of cover provided a haven for weeds to germinate. A clean crop also provides the cover crop with a head start and improves its ability to out-compete the weeds.
The project also examined the effectiveness of the 2+2 and 0 strategy (two non-glyphosate tactics in crop, plus two non-glyphosate tactics in fallow and zero survivors or incursions). This strategy was found to be effective, and the use of tools such as WEED-IT can provide an effective way to incorporate other herbicides, and particularly follow-up for effective survivor control.
Darling Downs grower Jamie Grant has more than a decade of experience growing cover crops and was a pioneer in including millet in his rotation as a dedicated cover crop. Jamie has modified his machinery and farming style, after much on-farm trial and experimentation.
Jamie Grant: experience and experimentation lights the way
Jamie is a dryland cotton grower near Jimbour, Darling Downs in South East Queensland. His current crop rotation is cotton every second year and a millet cover crop every other year. He has included French white millet as a cover crop in his rotation for nearly a decade and as a result, he has been able to change from cotton every third year to every second.
Jamie said his main reason for including the cover crop is to preserve soil moisture.
“The cover crop increases infiltration from rainfall, prevents the majority of run-off in larger events, and also prevents evaporation of moisture from the soil,” he said. “Weed management was not a major focus for the inclusion of the cover crop, however the cover from the millet does give an additional benefit in terms of weed control.”
Jamie also highlights the importance of a dedicated cover crop, as compared to a cash crop that is harvested for grain.
“The main purpose of the cover crop is to preserve moisture and cover,” he said. “When a crop is allowed to reach harvest maturity, it has taken extra moisture from the soil profile contrary to the objectives of a cover crop.”
Jamie has settled on French white millet as his cover crop, planted in 15-inch (38cm) rows. As the focus is to preserve soil moisture, millet is a short duration crop and can be grown to near maturity in six weeks from planting in October to December. In this time, the millet provides maximum cellulose to give the maximum length of cover from the stubble.
“While growing, the millet only uses approximately one foot or 30 cm of stored soil moisture,” Jamie said. “The gains in soil moisture has improved fallow efficiency from 30 per cent in fallow to 70 per cent with the cover crop.”
Before the inclusion of the cover crop, the soil profile required approximately 600mm of rainfall to refill. Now the profile is refilled after 300mm. The millet also creates enough cellulose that the cover remains adequate until cotton is planted the following season.
Jamie’s own research has shown that legumes tend to break down too quickly to provide the length of cover required, and French white millet has the right characteristics.
Jamie Grant grows cotton every second year rather than every third, using the moisture stored under the cover crop.
“I find that if I plant in October, I generally have 40 per cent cover the following November, when I’m ready to plant cotton,” Jamie said. “I don’t use sorghum as a cover crop, as the wider row spacing does not provide the cover needed, and the gaps in the stubble create a suitable microenvironment for weed germination and growth.”
“I also noticed that in lighter rainfall events in sorghum and wheat stubble, the rainfall runs down the stalks of the standing stubble and creates a wet patch at the base. This is where the weeds grow and creates weedy patches across the field. A good millet cover crop is more even and allows the rain to penetrate the stubble evenly, and the stubble cover reduces weed emergence and the need to spray.”
Cover crops must reach maturity to create the maximum amount of cellulose for longevity. Other crops such as sorghum, wheat and barley take too long to reach maturity and as a result use too much moisture.
The main weeds on Jamie’s farm include sowthistle, feathertop Rhodes grass and fleabane. Jamie places a high importance on weed control, however says “if you can grow good weeds, you can grow good crops”.
Jamie’s focus on weed management in the cover crop is to ensure adequate cover across the whole field, as gaps in cover create a haven for weeds.
“I do this by ensuring good germination, with quality seed, and I put as much effort into growing a good cover crop as I do growing cotton,” he said. “Double knocks are still an important part of the herbicide program and controlling weeds prior to crop emergence (both for millet and cotton) ensure the crop can get a head start to out compete the weeds. An in-crop spray of MCPA and Starane is always done in the millet to control volunteer cotton, however if a heavy cover crop is grown a spray to control volunteer cotton is not always needed.”
Jamie also uses a controlled traffic system (CTS), as he considers minimising soil compaction to be very important, has been using WeedSeeker technology on a large boom for a number of years, and is now using a SwarmFarm robot mounted with a WEED-IT sprayer across his fields.
The big boom is generally used for broadacre spraying, with the relevant herbicide mixture for the weeds present. The WeedSeeker, and now the SwarmFarm robot with the WEED-IT, will be mainly used to control weeds in fallows between rain events, and broadacre sprays on mass germinations. The spray rig is also rotated across the tramlines in the CTS, so that it does not constantly run up and down the same wheel tracks. This allows subsequent sprays to control weeds that were run over by the rig in the previous spray.
Jamie’s key learnings and advice to growers considering growing cover crops is to ‘work it backwards’.
“Grow the cover crop that can accumulate the most moisture, and then grow the cash crop that will take the best advantage of the moisture,” he said. “It is important to work out your moisture availability and your crop frequency. The moisture holding capacity of the soil will be better with a cover crop independent of soil type. The lower the capacity of the soil to hold moisture, the greater the effect evaporation has. This increases the importance of having a cover crop.”
Growing good cover
Jamie has spent a couple of years determining how to germinate and grow a good cover crop. He also stressed the importance of purchasing quality seed.
“Patience is the key,” he said. “It is important to do a good job with proper seedbed preparation at planting. An example of this when planting millet, is that it does not like to break through a crust while emerging.”
If Jamie gets enough rainfall for planting millet, he checks the forecast to ensure a further heavy rainfall event is not lik
Jamie finds that putting the effort into the millet crop means he reaps the benefit in the following cotton crop.
“A new tactic I’m considering is intercropping – planting millet between the cotton on a 60-inch row spacing (152 cm), and then spraying the millet out after three to four weeks,” he said. “This will increase ground cover in the cotton crop, with the benefits of increased weed competition, better rainfall infiltration and reduced moisture evaporation in-crop, for the sacrifice of some surface moisture that will evaporate in summer anyway.”
Jamie said it is also of key importance to let neighbours know what cover crops you have, to minimise the risk of spray drift, which will reduce their effectiveness by either killing areas or impeding growth and creating areas of less than adequate cover.
“Mapping fields with SataCrop is an important tool to do this,” he said.
Effect on soil moisture quantified
Cover crops serve multiple purposes in a cotton rotation, with research underway to quantify the effect on water infiltration and moisture holding capacity of soils.
Research is also underway in the Riverina as part of the ‘Staying ahead of weed evolution in changing cotton systems’ project. Researchers at NSW DPI in collaboration with CRDC, GRDC and Queensland DAF have run a series of experiments at the IREC trial site near Whitton in Southern NSW to better understand the effectiveness of incorporating cover crops into cotton systems. The aim of this research is to evaluate the benefits that cover crops could provide when incorporated into cotton systems, especially improved water infiltration and water holding capacity of soil.
An experiment looking at cover crop species and rotation types has been completed and is being analysed by a biometrician to gain insight into the soil water dynamics as influenced by the cover crops. Initial results suggest the type of cover used is less important than the amount of cover or biomass that is grown when it comes to influencing on yield.
This season a spray out timing experiment is being conducted to determine how much biomass is required by cover cropping to have an influence on infiltration and water holding capacity. During the winter fallow a cover crop mix was sown and subsequently sprayed out at different growth stages.
NSW DPI cotton research agronomist at Yanco, Hayden Petty says the intent was to achieve varying amounts of biomass into which cotton was planted. This will be compared to a fallow that is the control for the experiment.
“Cover crops offer many benefits to a cotton farming system, as research is showing with weed suppression and soil health,” Hayden said. “After harvest this year we will have fully analysed the data and will be in a position to offer a quantifiable effect on soil moisture.”
For more information, contact Hayden Petty
This article appears courtesy of the Cotton Research and Development Corporation (CRDC). It was published in the Autumn 2020 edition of CRDC’s Spotlight magazine: www.crdc.com.au/spotlight. Images courtesy Tom Quigley and Hayden Petty.
FTR grass demands attention to stop seed set
Feathertop Rhodes (FTR) grass is quickly becoming one of the biggest weed threats in Australian farming systems, demanding swift and decisive action.The vast number of seeds produced per plant and the species’ ability to germinate and establish on very small rainfall events, gives this weed a real competitive advantage, particularly in a fallow situation.
Feathertop Rhodes grass is a serious weed challenging no-till farming in Australia.
In the northern cropping region researchers have observed FTR grass (Chloris virgata) germinating almost all year round, at temperatures ranging from 15/5° to 35/25°C (day/night temperatures). While many seedlings that establish in winter are killed by frost, some will survive and it only takes a few plants to produce a large number of viable seeds for the next generation.
Recent research by Queensland Alliance for Agriculture and Food Innovation (QAAFI) weed researcher, Dr Bhagirath Chauhan has demonstrated that some populations of FTR grass are producing seed that is capable of germinating just two weeks after they mature.
“Night temperature does affect seed production of feathertop Rhodes grass so it is important to concentrate efforts on preventing germination or controlling these weed populations in spring and early summer,” says Dr Chauhan. “These early germinated populations are also more able to compete with summer crops and then set seed in-crop.”
Being able to tolerate both knockdown and residual (pre-emergent) herbicides, FTR grass can quickly gain a foothold in no-till farming systems. No-till and stubble retention also provide a favourable environment for germination, establishment and survival of FTR grass because of the moist soil conditions around the weed seed.
An integrated approach, like the WeedSmart Big 6, is needed to tackle this serious weed before it forces a return to full cultivation for weed control.
Diverse crop rotations – FTR grass is a year-round weed. Having diverse and competitive crops in rotation reduces the risk of a blow-out situation.
Mix and rotate herbicide MOA – FTR grass is not reliably controlled with a single post-emergent herbicide application. To be effective, the weeds must be sprayed when they are very young and not stressed.
At this stage, high rates of glyphosate with the best surfactants available, along with some group A products, can reduce the weed population. Residual herbicides like metolachlor, applied in late winter fallows, are very useful in moist soil conditions.
Herbicide is largely ineffective on FTR grass unless it is applied to small, actively growing seedlings.
Double knock glyphosate – Plan to follow any glyphosate application with a double knock to reduce the number of FTR grass survivors.
Grow competitive crops – FTR grass is sensitive to crop competition. All efforts to increase crop competition through crop and variety choice, narrower rows and stubble management will suppress FTR grass germination. Early weed control in sorghum can effectively suppress weed seed production of FTR grass plants that germinate later in the crop. A competitive cover crop could also be a valuable option.
FTR grass is susceptible to crop competition. Front – FTR from fallow, Middle – FTR from 1m row sorghum and Back – FTR from 0.5m row sorghum.
Stop weed seed set – This is the single-most effective tool to prevent an FTR grass incursion. FTR grass is a prolific seed producer and can quickly get out of hand. Initial invasions often occur as a weedy patch forms around a few ‘mother’ plants. Removing large FTR grass plants before they seed, using patch cultivation, chipping, hand pulling or fire, is the best option. Seed is easily spread in overland flow and on vehicles, machinery (particularly headers), people and animals. Extreme care is required when managing weedy patches to avoid spreading the problem.
Burning individual plants is one option to stop seed set on FTR grass.
Harvest weed seed control – FTR grass could be a good candidate for weed seed collection and destruction at harvest. One study has shown that as much as 93 per cent of the weed seed was retained (held) on the plant at the time of mungbean harvest (Chauhan et al., unpublished data). Increased crop competition tends to encourage taller FTR grass plants, making it easier to capture the seedheads at harvest.
“We also found that FTR grass seed on the soil surface is not viable after 12 months. Burying the seed lengthens the period that the seed remains viable, so unless the seedbank is completely buried to a depth of 5 cm or more and left undisturbed for more than 18 months, cultivation on its own might not be a good control tactic,” says Dr Chauhan. “If FTR grass seed is left on the surface, and no more seed is allowed to set, the seed bank will deplete in 12 months. In dry years the seed is likely to persist longer and some seed can be buried at planting or simply falling down cracks in the soil.”
Feathertop Rhodes grass is already widespread across Australia and it is easily transported to new areas during floods, on machinery and in hay. Roadsides, water channels, head ditches, and on-farm tracks are all sources of weed seed, which can then easily enter cropping areas. If hay is brought in, it is wise to feed out in defined areas so any FTR grass plants can be more readily seen and removed before they set seed. It is also important for agronomists, researchers and contractors to strictly follow biosecurity practices and ‘Come Clean, Go Clean’.
Find out more:
Weed biology insights to improve management of feathertop Rhodes grass and barnyard grass
Spring into action with fallow residuals
How do I deal with an emerging feathertop Rhodes grass problem?
Weed management programs for pigeonpea
WeedSmart Audio · WS – Pigeonpea – 5-min – Read – 3 01
Pigeonpea might not be well known in Australia, but there are more than a billion people in Asia and Africa who eat this dried grain legume in a variety of dishes, and global demand is high.
This demand is driving renewed interest in the crop, which was introduced to Australia in the 1970s but never developed into commercial production. In fact, it has only been grown as a trap-crop to monitor the incidence of Helicoverpa armigera (pod borer or bollworm) in Bt cotton crops.
This trial used paired row sowing (right) to give pigeonpea a competitive advantage over weeds compared to sowing in a wider configuration (50 cm, left).
As an emerging crop of importance to the grains and livestock industries, researchers have begun the task of investigating the agronomic requirements of pigeonpea in the Australian environment. Leading the way on the weed management front are researchers Gulshan Mahajan, Rao C. N. Rachaputi and Bhagirath Chauhan from the Queensland Alliance for Agriculture and Food Innovation (QAAFI), The University of Queensland at Gatton.
“Pigeonpea is of interest because it is a drought and heat-tolerant summer legume, and provides both grain for human consumption and high quality fodder for livestock,” says Dr Bhagirath Chauhan. “Its slow growth habit is a significant limitation, making the crop very susceptible to yield loss as a consequence of competition from weeds.”
In the summers of 2017 and 2018 the researchers tested the effect of row spacing and herbicide applications on crop yield. Their findings suggested that narrow row spacing (25 cm) and sequential herbicide applications provided effective weed control that preserved yield in pigeonpea.
Across the two years there was a marked difference in seasonal conditions and weed flora. In 2017, the only weed present at the site was giant pigweed but following a deep tillage operation there was a more complex community of weeds, particularly grasses, growing at the trial site in 2018.
“At the narrow (25 cm) and wide (50 cm) row configuration, a single application of the pre-emergent (pendimethalin) or a sequential application of pre-emergent and post-emergent (imazapic) herbicide reduced weed biomass and increased yield, compared to the no-control treatment,” he says. “When the sequential herbicide program was applied, it was equally effective in the narrow, wide and paired row configurations, giving growers more flexibility.”
Narrow row spacing (25 cm) and sequential herbicide applications provides effective weed control that preserves yield in pigeonpea.
“In seasons where conditions are too dry for the pre-emergent herbicide to be effective and there is a heavier reliance on the post-emergent herbicide alone, or where there are multiple weeds present, having the crop sown on narrower rows provides better weed control and preserves crop yield.”
In the right conditions, the sequential use of herbicides addresses the common problem of multiple flushes of weeds over summer.
2019 Top 5 WeedSmart experts, bulletins and podcasts
This year we have collected the topics that you, our audience, found the most interesting – based on how many people browsed, downloaded or listened to material on the website. Here are the results!
Starting with our expert columns where we ask industry leaders for their take on big decisions facing weed managers.
1. WeedSmart Expert
2. WeedSmart Expert
3. WeedSmart Expert
4. WeedSmart Expert
5. WeedSmart Expert
Next we will count down the top 5 articles on the bulletin board.
1. WeedSmart Bulletin
2. WeedSmart Bulletin
3. WeedSmart Bulletin
4. WeedSmart Bulletin
5. WeedSmart Bulletin
Last but far from least, here are the top three podcasts!
1. WeedSmart Podcast
2. WeedSmart Podcast
3. WeedSmart Podcast
The WeedSmart team looks forward to bringing you more great ideas from growers, agronomists and researchers across Australia to help manage weeds.
Trends in HWSC – the days of doing nothing are over
A simple online survey of 147 farmers from around Australia has added weight to the observations that growers are rapidly adopting harvest weed seed control methods that best suit their farms.
WeedSmart has previously conducted a similar survey in 2017 (269 respondents) and 2018 (95 respondents), and in 2014 a GRDC funded grower practices survey led by Rick Llewellyn from CSIRO, 600 growers answered questions related to the adoption of harvest weed seed control methods.
Peter Newman, WeedSmart and AHRI extension agronomist in Western Australia is thrilled to see more evidence of growers adopting harvest weed seed control tactics to their farming systems.
Peter Newman, WeedSmart and AHRI extension agronomist in Western Australia has been following the adoption trends closely. “We know that these surveys are biased and are not statistically rigorous, but together they are showing trends that we are also seeing in the field,” he says. “As growers invent, modify and trial different harvest weed seed control tools there is a rapid move toward actively managing survivor weeds at harvest and the adoption of tools that don’t involve burning.”
The most important and encouraging finding is that the percentage of growers ‘doing nothing’ to capture and destroy weed seeds present at harvest has declined dramatically since 2014 harvest, from almost 60 per cent, down to around 5 per cent predicted for 2022 harvest.
“This is a significant change in attitude and suggests that growers are taking the opportunity to tackle herbicide resistance head-on. When it comes to choosing the best tool for the job, growers can be assured that each of the tools available are equally effective at capturing and destroying weed seeds,” says Peter. “Some tools have a particular fit for certain situations, such as a chaff cart might be chosen for a mixed farming operation, or chaff tramlining chosen to help manage dust and erosion risk in a controlled traffic system.”
Adoption trends for harvest weed seed control tactics on Australian grain farms.
Around 10 per cent of growers are using and expect to continue using chaff carts and there is steady adoption of chaff tramlining, with almost 20 per cent of respondents planning to use a chaff deck this harvest.
“It is clear that narrow windrow burning has been superseded and few growers will be disappointed about having better options that conserve nutrients and involve less risk,” he says. “Less than five per cent of growers expect to still be doing narrow windrow burning in the 2022 harvest.”
While chaff lining has been rapidly adopted as a simple and cheap alternative to narrow windrow burning, many growers indicated that they would not be using this method in 2022. The trends indicate that many of these growers will be looking carefully at recent developments with weed seed impact mills.
“With three weed seed impact mill manufacturers now offering machines in Australia, growers are the beneficiaries of increased competition and many see this as the ultimate solution to weed seed, stubble and nutrient management at harvest,” says Peter.
Harvest weed seed control is one of the WeedSmart Big 6 suite of tactics to contain the threat of herbicide resistance in weeds.
AHRI Insight paper: Spoiled rotten – the sequel
AHRI Insight paper: HWSC is now mainstream
What do vineyards and fencelines have in common?
Keeping weed numbers down in crops is a high priority on most farms, yet herbicide resistance can quietly increase along fencelines and around infrastructure. Having a ‘set and forget’ weed control option for these areas could save money and arrest the evolution of herbicide resistance in weeds.
In vineyards the under-vine area is often kept bare using a limited number of suitable herbicides, opening the door to herbicide resistance. Populations of glyphosate-resistant annual ryegrass and fleabane have been confirmed in Australian vineyards and along fencelines and roadways.
Chris Penfold, research agronomist at the University of Adelaide, Roseworthy Campus says effective living mulches can provide a long-term management solution to stop fencelines being a source of herbicide resistant weeds.
Having worked previously in broadacre cropping, and more recently in the wine industry, research agronomist Chris Penfold, University of Adelaide is interested in identifying alternative ways to manage under-vine and mid-row areas in vineyards, which also has implications for fencelines on grain and mixed farming properties.
“In many cases it might be better to replace weeds on the fencelines with a competitive but palatable option,” he says. “In vineyards, the continual use of herbicides and cultivation for weed control under the vines has a long-term detrimental effect on soil health and grape quality. Consequently, our research aimed to identify cover crop species that would build soil health and conserve soil moisture for the vines. Since this is not a priority on grain farms, a range of other options might be chosen but the principle can remain – establish permanent cover and stop fenceline spraying,” says Chris.
Of the treatments Chris included in his trial, Kasbah cocksfoot and wallaby grass stood out as competitive species that did not spread into neighbouring areas and could be suitable for controlling weeds on fencelines.
“Kasbah provided good suppression of fleabane and thistles in vineyards, especially in irrigation areas. It is a summer dormant perennial that doesn’t recruit, even in vineyards. It did suppress vine growth so it isn’t a great option for vineyards but could work for fencelines,” says Chris. “The other competitive border species we tried was wallaby grass, a native perennial, which provided good cover, but seed is expensive and it can be hard to establish. By not applying herbicide to fencelines growers will save money, which can be partly re-directed to the establishment of effective living mulches to provide a long-term management solution to stop fencelines being a source of herbicide resistant weeds.”
Perennial species and self-regenerating annuals are the preferred options to minimise on-going management costs. The best species to establish will vary markedly between regions with prostrate saltbush having potential in drier areas, and lucerne and wallaby grass providing good control, even against caltrop, in other situations. In the vineyard situation a medic plus annual ryegrass cover provided good winter weed control and soil health benefits. By not spraying the annual ryegrass herbicide resistance does not evolve.
Native perennials such as wallaby grass, can provide good cover along the borders without spreading into the crop.
Another option Chris has investigated is in-crop grazing with sheep. With living mulches growing around the borders, sheep can be allowed to graze in established crops such as chickpea, faba bean, fenugreek and lupins, at light stocking density. The sheep will preferentially graze the in-crop weeds and may also assist with weed control along controlled traffic wheeltracks, especially if weed seed is directed onto the wheeltracks using a chaff-deck for harvest weed seed control.
“Sheep are selective grazers and lambs are more selective than older sheep,” says Chris. “Different sheep breeds also graze differently so these things need to be considered for each farming system. The principle to apply is to incorporate non-chemical management practices where possible into the farming system, which should then extend the useful life of herbicides.”
Where pastures are part of the crop rotation it can be as simple as establishing the pasture species along the fencelines and leaving them in place when the paddock rotates into the cropping phase. Similarly, the crop can be sown right up to the fenceline and either mown or baled for hay prior to harvest.
Nipping herbicide resistance in the bud in non-cropping areas is an important strategy often overlooked. These areas are often sprayed when weeds are large, often using the same herbicide (usually glyphosate) each time, and there is rarely any follow-up treatment of survivors. This is a recipe for rapid evolution of herbicide resistance.
Other resources for fenceline management:
And then there were three – impact mills on the market
Crop residue management is core business for Canadian company Redekop Manufacturing and now they have added harvest weed seed control to their offering to Australian grain growers.
Redekop have recently commercialised the Seed Control Unit (SCU), a weed seed impact mill that incorporates their well-known MAV straw chopper. This new impact mill makes three options commercially available on the Australian market – adding to the Australian-built iHSD and Seed Terminator.
Redekop Manufacturing’s president, Trevor Thiessen.
Redekop’s president, Trevor Thiessen said the company inadvertently became involved in harvest weed seed control when they noticed their chaff carts were being used in Australia to manage weeds rather than as a fodder collection system they were first invented for in the 1980s.
“Herbicide resistance in Canada is about five years behind the situation in Australia but it is definitely an increasing problem,” he said. “We have been working toward the development of the SCU since 2013 and tested the first units in 2017 in Australia and Canada.”
“Testing continued in 2018 to gather weed kill rates, which are consistently above 98 per cent, but there are some weeds and some conditions that we are yet to test.”
Breanne Tidemann, a research scientist in field agronomy and weed science with Agriculture and Agri-Food Canada in Lacombe, is conducting the independent testing of the SCU. Breanne has also been testing a tow-behind HSD unit in Canada since 2016 harvest.
The Redekop system combines the SCU chaff stream with the MAV straw stream, mixing the two streams in the same air flow at the back of the harvester to achieve improved residue spread and distribution.
Redekop Seed Control Unit (SCU).
Peter Newman, AHRI and WeedSmart Western agronomist said the recent expansion of options for growers wanting to use impact mills as their harvest weed seed control method was phenomenal.
“The three impact mills currently available are all integrated into harvesters, making harvest weed seed control very time efficient,” he said. “One important aspect that Redekop have really focussed on is achieving even spread of the crop residue out the back of the harvester. This is critical to the integrated mill systems achieving the most cost-effective outcome for growers by re-distributing nutrients across the full cutter-bar width.”
In a recent WeedSmart survey of over 100 growers around Australia, close to 50 per cent of growers plan to adopt a weed seed impact mill into their system within the next 3 to 5 years.
Redekop will have 20 SCUs operating in Western Australia this harvest with a team of support and research personnel on hand to further assess the units’ performance in Australian conditions and address any mechanical issues.
The SCUs are available as either a complete unit incorporating a MAV chopper suitable for all harvester types or as a purpose-built mill that fits onto a John Deere residue manager. Being integrated with the straw chopper, the SCU can be easily switched from chopper to chopper plus weed seed control.
Redekop are also involved in introducing the Australian-built EMAR chaff decks to Canadian growers as an entry level investment in harvest weed seed control.
Podcast – Redekop impact mill
Using your harvester to destroy weeds
Webinar – Comparing the iHSD and Seed Terminator
Double the action at WeedSmart Week 2019
Spreading the WeedSmart message
WeedSmart Week has been a highlight of the WeedSmart extension program for four years, bringing together growers, agronomists, researchers and agribusiness to learn and share experiences of tackling herbicide resistance in weeds.
The first event was held in Perth in 2016, then Wagga Wagga in 2017, Narrabri in 2018 and in 2019 demand was such that two events were held – one in Emerald, Queensland and another in Horsham, Victoria. Already plans are in place for the 2020 event in South Australia. You can register your interest here!
WeedSmart Week is an opportunity for experienced growers and agronomists to share their knowledge and gather new ideas for managing herbicide resistance in farming systems. Left to right: Tony Lockrey, AMPS Moree; Rod Collins, DAF Biloela and John Cameron, Bongeen cotton and grain grower.
The success of these events hinges on the quality of the grower and agronomist speakers on the forum day and the openness of the growers who welcome the bus loads of delegates onto their farms.
At this year’s events there were some other firsts, including trade displays and machinery and technology demonstrations.
Program manager, Lisa Mayer said the positive feedback has been overwhelming, with participants strongly backing the 3-day format of the event.
“The whole WeedSmart program is centred on getting practical messages about integrated weed management out to growers,” she said. “We have developed the ‘WeedSmart Big 6’ approach to controlling herbicide resistance, which is known to cost Australian grain growers an estimated $187 million in additional herbicide treatment costs, on top of the costs of extra integrated weed management practices.”
WeedSmart program manager Lisa Mayer with GRDC manager weeds, Dr Jason Emms at the SwarmFarm Robotics base at Gindi, south of Emerald in Central Queensland.
“Recognising the important differences in how these ‘Big 6’ tactics are applied in Northern and Southern region farming systems, we have launched region-specific recommendations for growers and agronomists to use as the foundation blocks for their individual weed management program to gain and keep the upper hand on weed numbers.”
One of the unique aspects of the WeedSmart program is its firm partnership with industry. The program’s main funding body continues to be the GRDC with significant sponsorship funding flowing from the major crop protection and several machinery and seed companies.
WeedSmart has most recently welcomed agricultural machinery manufacturer Primary Sales as a silver sponsor, joining platinum sponsor GRDC, gold sponsors CRDC, Nufarm, Sinochem, Syngenta, Monsanto and Bayer and silver sponsors Pioneer Seeds, FMC, BASF and Corteva.
Harvest weed seed control tools, including impact mills and chaff decks were on show for growers at the Horsham WeedSmart Week event in August.
“Our sponsors are very committed to the WeedSmart ethos of broadening weed control programs to keep herbicides as an effective long-term option for growers,” said Ms Mayer. “It is abundantly clear that the era of herbicide-only weed control is over and the sooner growers adopt a more integrated approach that includes greater crop competition, harvest weed seed control and effective crop rotations, as well as judicious use of herbicides, the more options they will have in the future.”
At the Emerald WeedSmart Week event the limelight shone on emerging technologies such as strategic tillage weed removal, the SwarmFarm robotic platform and the weed detection and spraying systems being developed by Bilberry, Autoweed, InFarm, Agrifac and WeedIT for in-crop and fallow weed management.
CQ farmer Don Sampson (pictured with AHRI northern agronomist Paul McIntosh) demonstrated his 70ft blade plough that cuts weeds off at the roots without inverting the soil, maintaining soil moisture in his conservation farming system.
Guillaume Jourdain, Bilberry CEO spoke about green on green weed detection and spraying technology at both the Emerald and Horsham WeedSmart Week events.
Harvest weed seed control was the focus of the machinery and technology demonstrations at WeedSmart Week Horsham with growers having the opportunity to look at the latest developments in the Seed Terminator and vertical iHSD impact mills and Emar chaff decks. Primary Sales also provided unprecedented access to Martin Reichelt, an international harvester expert who challenged delegates to rethink some of their harvesting strategies and settings to maximise the efficacy of harvest weed seed control while also minimising grain losses.
The bus tours continue to be an immensely valuable and enjoyable component of the WeedSmart Week events with leading growers sharing their successes and their learnings as they have pieced together a weed control program that suits their farm and their way of working.
Horsham mixed farmer Sam Eagle explained the value of containment paddocks for managing sheep grazing in a cropping system.
The 2019 events also benefited from the support of local grower groups – the Central Queensland Grower Solutions Group and the Birchip Cropping Group.
The WeedSmart team is looking forward to bringing you WeedSmart Week 2020 somewhere in South Australia! WeedSmart national team together at Horsham (left to right) Greg Condon (AHRI southern agronomist), Cindy Benjamin (WeedSmart content producer), Peter Newman (AHRI western agronomist), Jessica Strauss (AHRI communications lead), Kirrily Condon (AHRI southern agronomist) and Lisa Mayer (AHRI program manager). Missing from photo: Paul McIntosh (AHRI northern agronomist).
Podcasts on the events
Stepping into chaff lining
Peter Newman, AHRI / Weedsmart Western region agronomist, is a firm advocate of harvest weed seed control (HWSC). In this practical publication Peter provides all the details you need to get started with this important tactic in the war against herbicide resistant weeds.
Chaff lining chute.
Use this guide to ensure you are:
1. Getting the weed seeds into the front of the harvester
2. Getting weed seeds out of the rotor
3. Keeping weed seeds in the chaff stream
4. Deliver weed seeds into the HWSC tool – chaff line chutes
Comparison of chaff lining and chaff tramlining
Download ‘Tools and Tips – Setting up for chaff lining’
WeedSmart Big 6 – including Harvest weed seed control
No water, just weeds? Managing weeds in irrigation channels
Are your channels a source of weeds on your farm?
Irrigation channels require regular monitoring as they are often a source for new weed incursions. Weed seeds can enter farms from irrigation water and any new weeds emerging need to be removed prior to seed set. Retaining irrigation water on farm can help to limit any potential spread.
Weeds in irrigation channels are an important source of weeds.
What do we know?
Channels are a source of seeds that can move into cotton fields adding to the weed seed bank.
Weeds in channels are a potential host for disease and insect pests.
They can interrupt water delivery reducing irrigation efficiency.
Large weed infestations can provide habitat for feral pests.
Larger weeds can also undermine the integrity and stability of the channel bank.
What are the options?
In addition to knockdown and residual herbicides always include mechanical removal as part of an integrated approach to weed management.
Valor (Group G) herbicide contains flumioxazin and is registered for knockdown and residual control of broadleaf and grass weeds on irrigation channel banks. It has low volatility and binds strongly to the soil so the risk of movement is very low. Valor binds tightly to the soil after 25mm of rain, if that doesn’t occur within 3 weeks after application the channel will require flushing and the waste water retained on farm. It is not degraded by solar radiation even if exposed for weeks prior to water or rainfall.
Pendimethalin (Group D) is a herbicide which provides residual control predominantly of grass weed species. Pendimethalin is very tightly bound to soil particles and has very low solubility; meaning it stays where it is applied. Pendimethalin should be applied to the bank after grading or reshaping and if rainfall does not occur for 14 days the channel should be filled with water and then waste retained for pre-irrigation of cotton fields.
Diuron (Group C) is a herbicide which provides residual control of a range of grass and broadleaf weeds. Diuron has limited mobility binding tightly to the soil, extremely low volatility and has a relatively low solubility rating. Application needs to be onto moist bare soil and prior to rainfall to fix the herbicide to the soil. If rainfall does not occur fill the channel, let stand for 72 hours and then drain the water into waste.
Glyphosate (Group M) is a knockdown herbicide with activity on a large number of weeds common to irrigation channels. The overuse of glyphosate for weed control in non-field areas is a contributing factor to the development of herbicide resistance; thus its use around channels, road sides and non-field areas should be restricted. Any survivors from glyphosate application need to be removed to prevent weed seeds topping up the soil seedbank with a potentially resistant population.
Amitrole-T (Group Q) is a knockdown herbicide that controls a range of seedling grasses and young broadleaf weeds. Using Amitrole-T as a substitute for glyphosate will help to reduce the likelihood of glyphosate resistance developing.
The importance of pre-emergent and residual herbicides
Getting the best out of any herbicide is important, none more so than glyphosate.
By incorporating pre-emergent herbicides into our planting program we reduce the emergence of weeds in crop allowing growers to target a small population of weeds reducing the risk of herbicide resistance developing. Running the weed seed bank down and targeting small weed numbers is a robust strategy for ensuring complete weed control. It’s a numbers game, low weed numbers means there is less likelihood of resistant individuals within the population, and large weed numbers increases the risk of resistant individuals present in the population.
Demonstration trials at Wee Waa and Whitton in 2018-19 highlighted this clearly. In addition to the risk of resistance from spraying large weed numbers the yield penalties from these early weedy treatments were significant. A 3.5b/ha difference between the weedy control and those treatments with pendithethalin or diuron reinforces the clear message of diverse weed control options.
Learn more in this short video from CottonInfo’s weed tech lead Eric Koetz:
Further information: CottonInfo weed management page
Spring into action with fallow residuals
While frost on winter crops is often growers’ main concern in August and September, this is also the time when some summer weeds start germinating if conditions are favourable. A spring rainfall event, followed by a week or two of warmer weather, can quickly kick off the season for summer weeds.
Mark Congreve, Consultant with Independent Consultants Australia Network, says fleabane, sowthistle and feathertop Rhodes can all start germinating as early as August in northern regions when temperatures are suitable.
Mark Congreve, consultant with Independent Consultants Australia Network, says summer growing weeds that establish in late winter and early spring may result in plants that are large and very difficult to control with knockdowns if control is left until after the busy harvest period.
“Establishment at this time of year may result in plants that are large and very difficult to control with knockdowns if control is left until after the busy harvest period,” he says. “Once this happens the only options for control are a robust double-knock herbicide strategy, or tillage.”
The full canopy cover in a dense winter crop generally prevents most germinations within the crop, but these weeds can establish in open crops, in missed rows or wide guess rows, around crop edges or in winter fallows.
Mark suggests that pre-emergent herbicides applied in late winter or early spring fallow, before the first spring storms, can play an important role in managing these early germinations of ‘summer’ weeds, helping create a weed-free winter-spring fallows until it is time to sow a summer crop.
“This is easiest when a paddock has been ear-marked for a specific summer crop,” he says. “Rotation planning is really important – where you know what you will be planting, there are normally one or more options with acceptable plant-back periods for most crop choices. Where you are unsure about what crop will be planted into the paddock, then decisions are more difficult.”
Pre-emergent herbicides applied in late winter or early spring fallow, before the first spring storms, can play an important role in managing these early germinations of ‘summer’ weeds, helping to create a weed-free winter-spring fallow until it is time to sow a summer crop. Photo: Ben Fleet
To ‘keep the options open’ growers are restricted to using products with shorter plant-back periods, and therefore less residual control. If using a product with potentially damaging residual activity on subsequent crops, growers are reliant on further rainfall to breakdown the herbicide in the soil prior to summer crop planting.
“In some situations, it may be possible to plant the summer crop any time after the residual is applied in spring,” says Mark. “A good example of this is using Dual®Gold for feathertop Rhodes grass control in paddocks going to sorghum.”
For other combinations of residual herbicides and summer crops a plant-back period may be required. Mark said it is very important to use the label information to determine the level of risk involved in applying a particular product andjudge whether it is safe to plant the summer crop or not.
“Where plant-back periods exist, the breakdown of these herbicides needs a combination of time and soil moisture over the warmer months, so it is important to look at how the rain has fallen, as well as the totals,” he says. “Having the soil surface wet for a few weeks from regular rainfall events during these warmer months will support more microbial breakdown of the herbicide than one storm event that delivered the same quantity of rainfall, followed by weeks of dry weather.”
Ideally, a well-timed spring residual herbicide will keep the fallow clean until the summer crop planting window opens. Assuming the appropriate plant-backs have been met, an effective knock-down herbicide may be needed to remove weeds germinating on the planting rain, should the spring residual herbicide be running out.
The decision around the choice of additional pre-emergent applied at planting will depend upon the length of residual expected from the spring application, the known weed pressure in the field, the availability of inter-row cultivation or post-emergent in-crop herbicide options and the predicted rainfall outlook.
Growers and agronomists interested in learning more about the benefits and risks of pre-emergent herbicides can access a free online course at www.diversityera.com, presented by Mr Congreve and Dr Chris Preston.
Early weed control benefits summer crops
CQ grain growers endorse WeedSmart Big 6
Weed management moves to a whole new level when you add the word ‘integrated’. This is the driving force behind the WeedSmart Big 6 approach, which suggests that growers implement as many of these six key tactics as possible into their crop management programs.
Herbicide resistant weeds might not be widespread in Central Queensland yet, but all the indications are that the problem is flying just under the radar. Following the discovery of the world’s first population of glyphosate resistant sweet summer grass near Emerald, random weed surveys have since confirmed glyphosate resistance in both feathertop Rhodes grass and fleabane samples collected in the region.
Members of the Central Queensland Grower Solutions Group have been working hard to build an integrated weed management system that suits their farms. In doing so they are ticking off many of the ‘Big 6’ tactics each season. These tactics are summarised as:
Crop and pasture rotation
Double knock to protect glyphosate
Mix and rotate herbicide groups
Stop weed seed set
Harvest weed seed control
In August last year, twelve Central Queensland growers attended the 2018 WeedSmart Week in Narrabri as part of a 6-day fact-finding tour through southern Queensland and northern NSW, delivered by the CQ Grower Solutions Group.
Kurt Mayne and Scott Becker were among the group, and this year they are backing WeedSmart Week in their own backyard of Emerald, Queensland. This practical and thought-provoking event also has the solid backing of the CQ Grower Solutions Group, a joint initiative of GRDC and Queensland Department of Agriculture and Fisheries (DAF).
Rolleston grain grower, Kurt Mayne returned from the study tour with a realistic view of the risk of herbicide resistance and a firm commitment to getting himself on the front foot before it starts to impact on the profitability of his business.
“One of the stand-out tools that we saw being used very effectively was optical sprayer technology,” said Kurt. “When I returned from the tour last year, I purchased a WeedIT sprayer to prolong the effective life of the chemistry that we currently have available.”
CQ grain grower, Kurt Mayne is impressed with the benefits that have come with the addition of an optical sprayer to his weed control program. Kurt will be part of an expert panel at WeedSmart Week in Emerald to discuss the pros and cons of this technology.
“In our farming system it is hard to incorporate pre-emergent herbicides in the fallow because that can restrict our opportunity cropping options. The optical sprayer makes fallow weed management much more effective, and when that’s combined with pulses in the rotation we are able to keep on top of grass weeds like feathertop Rhodes grass, which was getting increasingly difficult to manage.”
With WeedSmart Week being held for the first time in Central Queensland, Kurt is looking forward to the opportunity to hear how other growers are contending with herbicide resistance in weeds and how different ideas and technologies could be implemented in the region. Kurt will be part of the spray technology discussion panel at the forum on 13 August.
Farming near Moura, Scott and Kelly Becker are keen to trial harvest weed seed control as a possible addition to their weed management program. Being fully aware of the impact herbicide resistance could have on their family farming business, the Beckers have been proactive with chipping out small patches of feathertop Rhodes grass in sorghum.
“We are planning our cropping program four or five years ahead, mainly to manage stubble cover and to rotate herbicide modes of action,” said Scott. “We have incorporated most of the WeedSmart Big 6 tactics to keep weed numbers low and think that chaff lining could be a useful way to contain any weed seeds produced in-crop.”
Keeping weed numbers low is high priority for Scott Becker, Moura, who is keen to find a practical harvest weed seed control option suited to CQ farming systems and weed spectrum.
“It’s a numbers game when it comes to weed management and the only way we can win is to be doing everything possible to keep numbers low and prevent seed set where possible,” he said.
Hayley Eames, Department of Agriculture and Fisheries development extension officer said the CQ Grower Solutions project has been delivering a range of extension activities aimed at addressing production constraints around five key themes, including integrated management of hard to control weed species, since 2015.
“Herbicide resistance is ever increasing in Central Queensland and although individual weed control tactics are quite well understood in the region there needs to be more integration of control measures,” she said. “Growers have relied on rotation from summer to winter crops and from cereals to pulses and this has worked well for a long time. There is scope to include other strategies though, such as strategic use of pre-emergent herbicides and harvest weed seed control.”
DAF is supporting WeedSmart Week in Emerald as a rare opportunity for local grain and cotton growers to focus on managing the looming threat of herbicide resistance in weeds. The 2.5-day program will begin with a 1-day forum at the McIndoe Function Centre, Emerald on 13 August. The following day will be filled with a bus tour to farms around Emerald where growers have put in place integrated weed management programs to minimise the impact of herbicide resistance on their businesses. The final part of the program is a half-day tour of the SwarmFarm Robotics base at Gindie on Thursday 15 August to see and discuss cutting-edge technologies such as optical weed sensing for spraying and chipping, robots and emerging ‘green-on-green’ spray sensors.
Register for this important 3-day event before 31 July for the ‘early bird’ single ticket price of $130, guaranteeing a seat on both the bus tour days as well as the forum, all fully catered, at https://www.weedsmart.org.au/weedsmart-week-emerald/