Key messages
- Spend now, save later - having clean, weed-free stubbles over summer can help prevent losses of valuable soil water and nitrogen stores
- Timing is key, aim to spray weeds 2-4 weeks after they emerge
- Make a plan of which paddocks need to be tackled first based on weed numbers, leaf and root size
- Use best practice spraying practices to ensure weed control is effective and efficient and to prevent off-target damage
Following heavy rainfall over the past few weeks, many of you will be hopping out of the harvester and into the sprayer, with the aim of getting on top of summer weeds before hopefully having a well-earned break over the holidays!
There's a lot to consider with summer spraying, from timing to equipment setup and weather considerations, and this blog provides some practical tips to help you get the best results from this summer's spraying program.
Timing is everything when it comes to summer weed control. It's important to assess your paddocks individually and speak to your agronomist when developing a summer spray program. Start by identifying the range of weeds present, noting size (including root systems) and the number of plants. Use the GRDC common weed guide as a quick reference when identifying weeds.
Put together a hitlist on which paddocks require immediate attention and others that can wait while you get around the farm. Spraying weeds when they are small, actively growing and not under moisture stress should improve the effectiveness of the chemical application and reduce the risk of any build up of herbicide resistance.
Summer weeds can grow and set seed quickly, making late intervention less effective and more costly. Leaving weeds to grow over summer will increase future weed issues by increasing the weed seed bank. Research has also shown that spraying summer weeds soon after emergence can help the paddock store more soil moisture and nitrogen, which could be valuable later in the season.
Early trials for spraying summer weeds have shown that an additional 15-20mm of stored soil water and 10-30kg/ha retained nitrogen compared to leaving weeds uncontrolled. Learn more.Make sure you plan ahead and think about crops you will be planting in 2025. Checking plant-back periods and the required rainfall totals for residual herbicides will reduce the risks of poor establishment or failed germination at sowing time. Pulse crops are particularly sensitive to residual chemicals in the soil.
Oil adjuvants can increase the effectiveness of your summer spraying by improving the retention of droplets on the weed leaf surface and penetration into the leaf. Ammonium sulphate (SOA) can improve herbicide performance also through improving penetration into the plant and buffering high pH water.
Targeting a water rate of above 50L/ha, 80-100L/ha is usually recommended, depending on the chemicals to be applied, and the stubble load, so it's important to consult your agronomist for correct rate for your situation. Higher water rates are recommended to reduce the risk of drift and to ensure optimal coverage of weeds.
Always check the weather conditions before and during spraying, and be aware of any hazardous inversion layers which can cause off-target damage to crops. During inversion events, volatile vapour drift (which can occur with herbicides such as esters), can cause damage to sensitive broadleaf crops such as cotton and other horticultural crops many kilometres away. An atmospheric inversion layer occurs when cool air is trapped near the soil surface by a layer of hot air above; this creates the opportunity for small spray droplets and vapurs, which are suspended near the surface, to move off target. This normally occurs on clear, calm mornings and nights, so it's recommended to spray only when wind speeds are between 3-20km/hr. Always follow the label directions.
Riverine Plains is supporting farmers and contractors to make more informed spraying decisions using real-time data from the newly upgraded Riverine Plains weather station network. The stations, located across the Riverine Plains, provide wind speed, temperature, rainfall and spray conditions information.
Setting up your sprayer correctly will help avoid issues with spray drift. Some tips include:
Refer to the GRDC standard nozzle selection guide for more information. Want a hard copy for the shed? We have some available in the office, let us know and we can distribute!
Follow these rules for successful summer spraying:
It is also very important to keep detailed records of when, what and how you spray. If you do not use program such as Agworld to record your spray applications, the NSW Environment Protection Authority have developed a basic record keeping form template.
Read more on what records you are legally required to keep in NSW and Victoria.
After application, continue monitoring paddocks to assess the effectiveness of your spray and detect any regrowth or new weed outbreaks.
As it is still early in the summer season, the probability of more rain prior to sowing next year is high. Think about budgeting for multiple summer spray applications or complete a double knock down prior to sowing. In the case of more rain early next year, speak to your agronomist about the best options for you. Try to be proactive with your weed management strategy, use the correct application techniques and be mindful of weather conditions to maximise your spray efficiency and minimise off-target impact.
The GRDC GrowNotes Spray application manual is a valuable resource with a range of information, covering a range of topics to suit people new to spray application up to the experienced boom operator.
A guide to summer spraying | CropSmart
5 tips summer spraying | AW Vater
Hazardous inversion and spray drift | Weed Smart
Adjuvants, oils, surfactants and other additives for farm chemicals | Weed Smart
Summer weed control 2024 | CropSmart
Protect next seasons profits with summer weed control | GRDC
GRDC GrowNotes Spray application manual
Pesticides compulsory record keeping | NSW Environment Protection Authority