Building profitable and sustainable rice farming systems through better fallow and in-crop weed management
Published: September 2026
What is integrated weed management?
Integrated weed management (IWM) is a long-term approach to weed control that combines multiple tactics to reduce weed populations and minimise herbicide resistance over time.
Rather than relying on a single tool, such as herbicides, IWM uses a combination of chemical, cultural, biological and mechanical strategies to manage weeds while protecting long-term productivity.
“Integrated weed management is essentially an approach where you're not just relying on one particular tool in the toolkit.” - Meg Brown, Elders Griffith Broadacre Agronomist
What does integrated weed management look like?
Successful IWM programs use a range of complementary practices to reduce weed pressure, protect valuable chemistry and improve whole-farm profitability.
Cover crops
Suppress weeds through crop competition and ground cover.
Improve soil structure and reduce erosion.
Increase soil organic matter and nutrient cycling.
Provide opportunities to introduce additional herbicide modes of action.
Herbicides
Rotate herbicide modes of action to delay resistance.
Use residual herbicides strategically to control weeds before they emerge.
Target the right weed at the right growth stage.
Ensure the spray boom is set up to minimise drift and maximise the right amount of chemical getting to the target.
Strategic cultivation
Use cultivation where appropriate to manage specific weed species.
Understand how cultivation affects weed seedbank dynamics and future weed pressure.
Crop rotation
Increase weed control options by diversifying herbicide programs.
Create additional opportunities for seedbank management through hay, silage, green manure or brown manure crops.
Spread production and seasonal risk across the farming system.
Early intervention
Target weeds while they are small and actively growing.
Aim to control emerged weeds within 10 days of germination, particularly during summer fallows.
Reduce competition for water and nutrients before weeds become established.
Soil and water management
Reduce reliance on single herbicide groups and repeated cultivation.
Improve soil health and water use efficiency.
Maintain more soil moisture and nutrients for future crops.
Why should IWM be a priority?
Every weed that survives has the potential to set seed, increase future weed pressure and contribute to herbicide resistance.
Effective fallow weed control delivers benefits well beyond the current season by:
Conserving valuable soil moisture.
Retaining plant-available nitrogen and nutrients.
Reducing weed seedbanks over time.
Improving planting conditions.
Supporting more effective herbicide programs.
Increasing future rotational opportunities.
Weeds growing during fallow periods compete directly with future crops for water, nutrients and profitability.
"Start early with your fallow management. Don't rely on one particular tool. Give yourself the opportunity to have a couple of goes at it."
Effective fallow management today helps set up the next crop for success.
What role can cover crops play?
Cover crops are becoming an increasingly valuable tool within integrated weed management programs.
Benefits may include:
Weed suppression through crop competition.
Additional herbicide options within the farming system.
Improved soil structure and soil health.
Increased soil organic matter.
Reduced erosion and topsoil loss.
Improved nitrogen cycling, particularly from pulse species such as vetch.
Greater farming system resilience.
Cover crops should be viewed as another tool in the toolbox rather than a standalone weed control strategy.
Before returning a paddock to rice
Take time to understand the history of each paddock before finalising your weed management strategy.
Checklist:
✓ What weed species have been present in previous crops or fallows?
✓ Which herbicide modes of action have been used in recent seasons?
✓ Are there any potential herbicide resistance concerns?
✓ Are there plant-back restrictions from previous residual herbicides in your rotation?
✓ What is the current weed seedbank likely to look like?
Getting the best result from herbicide inputs this season
Use an integrated approach so each herbicide remains effective for as long as possible. This is particularly important in rice, where there are limited products and modes of action available.
Be alert to barnyard grass resistance risk. Glyphosate and Group 1 resistance has already been recorded in northern regions, and Group 1 resistance was detected at Murrami in 2019. Protecting Group 1 chemistry in the Riverina is critical, because increased pressure on Agixa® may lift the risk of resistance developing more quickly.
Apply paraquat at the recommended label rate and target 1–2 leaf barnyard grass. Best results come when weeds are small, actively growing and not moisture or temperature stressed.
Consider splitting the three-way mix where conditions allow: paraquat as soon as the field is trafficable, followed by pendimethalin and clomazone immediately before the second flush. This can support better timing, activation and weed control.
Avoid using a second Agixa® application to clean up escapes, as this increases resistance risk. Instead, focus on:
Reducing the weed seedbank through strong summer fallow management.
Optimising post-sow, pre-emergent paraquat timing.
Using full rates of pendimethalin and clomazone before the second flush.
Considering alternative modes of action, such as propanil where appropriate and label conditions allow.
Applying herbicides to small, actively growing weeds.
Considering a pendimethalin top-up with Agixa®, depending on the time since the three-way mix application.
Managing permanent water after Agixa® to reduce later germinations in areas exposed to wetting and drying cycles.
Avoiding incompatible tank mixes, including Basagran® M60 or Fastac® with Agixa®.
Using strong crop competition through plant population and nutrition to reduce seed set from survivors.
Managing channels, banks and non-crop areas with alternative modes of action and, where suitable, residual products or physical control such as slashing or cultivation. Channels and bank spraying: The angles of banks and channels can significantly reduce the rate of applied products. You are applying over a larger area than the boom width due to the slope, if you measured the depth/slope you could be spraying over 20% more area than your boom width which will significantly reduce your product application rate. Underdosing these areas significantly increases the resistance risk, especially with successive germinations every time the area wets and dries with each irrigation event.
Hormesis: this is a phenomenon which results in a fitness benefit from sub lethal application rates of products to species of weeds, especially barnyard grass and fleabane. Plants grow more vigorously and can produce significantly more seed than untreated plants, increasing the risk and speed of resistance development. Banks, channels and field margins are the highest risk areas for this to occur. Paying particular attention to applying full rates to field margins and avoid stressed plants in these areas will minimize the risk of this occurring.
If you suspect barnyard grass resistance
Not every control failure is resistance — incorrect timing, rate, weed size, or water management are more common causes of poor results. However, if you see a consistent pattern of survivors after correct label application, treat it seriously and work through the following steps.
Rule out application issues first. Check the label rate, weed growth stage, application timing, coverage and water management before and after application.
Confirm the weed identification. Check that the plant is barnyard grass and not another grass weed, as different species and biotypes can vary in appearance and susceptibility.
Record the pattern. Note whether escapes are scattered or in patches, whether the same areas fail each year, and what products, rates and timings were used.
Collect and submit a seed sample. Send seed from surviving mature plants to the Charles Sturt University Herbicide Resistance Screening service for testing.
Talk to your agronomist, NSW DPIRD or Rice Extension. They can help review paddock history, interpret results and adjust the program.
Stop using the suspect mode of action in that area. Avoid repeating the same chemistry on the affected paddock while the risk is being assessed.
Use a different mode of action for clean-up where appropriate. Control survivors before they set seed, following label directions and agronomic advice.
Prevent seed set and spread. Spot-spray or rogue patches where practical, harvest affected areas separately or last, and clean down machinery before moving to clean paddocks.
Plan a genuine rotation break. Consider a winter crop, pasture, summer row crop or long fallow rather than relying only on another rice herbicide.
Update paddock records. Keep a weed pressure and herbicide-use history so resistance risk and rotation planning can be tracked over time.
Looking ahead to a non-ponded rice future
As rice production systems continue to evolve, weed management will become increasingly important.
Reduced ponding periods and changing water management practices may create opportunities for different weed species to persist and thrive. This means growers will need to place greater emphasis on:
Early weed control.
Fallow management.
Diverse weed control strategies.
Protecting herbicide effectiveness.
Key takeaways
Integrated weed management uses multiple tactics rather than relying on a single control method.
Successful weed management starts with a plan and a long-term view of the farming system.
Early intervention is the most cost-effective approach to controlling weeds.
Effective fallow management conserves water and nutrients while reducing future weed pressure.
Weed management decisions should be tailored to the weed species present, soil type and planned crop rotation.
The actions taken today will influence productivity, profitability and weed pressure for seasons to come.
“Just be mindful of what you're doing in fields is going to ultimately impact the following season.”
Resources
GRDC Barnyard Grass Management resource: Integrated weed management of barnyard grasses
Craig Day Hormesis video: Hormesis in weeds