Summer Weed Control 2025 - 2026
Controlling summer-growing weeds offers a reliable return on investment. Some new data from the Australian Government Future Drought Fund trials confirmed what we know and identified the following. The flux tower saw that over the summer, weeds used 2mm/day of water. This means there is a 2mm loss of water in the soil per day that weeds will use if they cannot be sprayed in time. This is critical information with a lack of rainfall, and when soil moisture is key for the following year’s sowing”. The data also showed that weeds stopped using water within two days of the first herbicides being applied.
If we put that into practical terms...
- 2mm water loss/day from summer growing weeds
- wheat WUE 25kg/mm/ha
- 50kg/ha/day loss
- @$350/t $17.50/ha/day
- Over a 7-day period, the potential loss jumps up to $122.50/ha
- A common Summer Weed Mix of Smart Loaded 540, Triclopyr, LV Ester, AMS, Smart Penetrator will cost roughly $17/ha. Each day missed, you lose the cost of the inputs (excluding application) to control the weeds. Plus, if the weeds become older and larger, they will require higher rates of herbicide
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Key points to achieve better weed control
Knockdown
- The first spray in summer is the most critical. Trying to kill larger, half-dead weeds later is very difficult
Rotation and residuals
- There is always a discussion around residual herbicides for summer weeds
- This has the potential to save money and an additional pass, but the recommendation and choice is a complex one.
- Careful consideration should be given to rotations and locking in your following crop based on herbicide residual
- Consider the weeds the herbicide will control and if it is economically viable. A residual might prevent heliotrope/Potato Weed from emerging but will not control volunteer cereals, so you have to spray anyway
Budget for three sprays
- A lot of agronomists we talk to are budgeting for three sprays
- This can become hectic for paddock work and for input supplies. Carefully forecast and budget activities and products.
This could be a long-drawn-out harvest and summer
- Look after yourself and your clients
- Simplify systems, logistics and processes
Spray Quality (Droplet size) Reminder • 2,4-D
No Smaller than Very Coarse (Summertime Extremely/ Ultra Coarse recommended) 2,4-D summary:
- Do not spray when a surface temperature inversion is present
- Applicators must now use “at least” a Very Coarse (VC) spray quality
- When using a boom sprayer, boom heights must be 0.5m or lower above the target canopy
- Downwind buffers now apply (typically less than 50m, subject to rate and product being applied) between application sites, downwind sensitive crops and environmentally sensitive aquatic areas
- Additional record keeping is required. Operators need to update spray records, with greater detail, within 24 hours of application and keep these records for a minimum of two years
- Two newer 2,4-D products like Nufarm Dropzone and Corteva Cox-D may offer reduced off-target damage potential and improved droplet deposition
Other Herbicides
- Glyphosate: Coarse to Very Coarse droplet Registered (Very Coarse or greater recommended)
- Garlon 600: Medium to Coarse on label (Coarse or greater recommended)
- Paraquat: Medium on label (Coarse or greater recommended with high water rates in summer)
Adjuvants
Ammonium Sulphate (AMS) should be in all tank mixes.
- AMS reduced herbicide antagonism
- Softens hard water to reduce herbicide tie-up
- Improves Glyphosate performance, even in good quality water
An esterified oil will form the foundation of your summer weed brews. A product like Smart Penetrator. When the target weeds are mostly broadleaf, you will use an oil. When the majority of weeds are grasses or volunteer cereals you should switch to a wetter like Smart 700 Spray. It's always best to check with your agronomist for specific recommendations and situations.
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