Summer Weed Control

Controlling Summer Weeds is a very good investment, but timing is critical. Controlling summer weeds soon after emergence when they are very small is one of the best investments you can make:

• For every dollar invested, growers stand to make $3.53 (Hunt, 2011). Farmer and Agronomic experience tell us that this can be as much as $5-10 per dollar invested
• You maintain valuable stored soil water
• Early spraying trials for summer weeds delivered an additional 15-20mm of stored soil water and 10-30kg/ha retained nitrogen compared to leaving weeds uncontrolled (Oliver et al, 2023)
• You maintain soil nitrogen reserves. Often budgeting on an additional $20-$50/ha of additional stored Nitrogen via a clean summer fallow
• Spray small weeds as soon as possible. Stop them using water and nitrogen
• Use best management practicing with your spray application

Factors in planning a weed control strategy:

• What weeds are present?
  • Correctly identify the weeds
  • Assess the density of each weed population
  • Target the weeds with the correct products and rates
• How old and fresh are the weeds?
  • Weed size and age are very important
  • Check the weed age and root size. When weeds such as marshmallow become stressed, they can appear as small weeds on the surface, but they may have a large root system
  • Spraying as soon as you have weeds at the 2-3 leaf stage is ideal
  • Spraying small weeds actively growing with roots active in moist soil will lead to the best results
• Cropping intentions 2025- plant back period consideration
  • Using residual herbicides can be a very effective strategy. Be mindful that these herbicides require rainfall to wash them into the soil to be active and effective
  • Study the product label and refer to your Agronomist before using residual herbicides. They may impact or alter your crop rotation plans
• Environmental/weather conditions at spraying
  • Do not spray if a dangerous temperature inversion is present
  • It is recommended not to spray at night
  • Spray only when wind speeds are between 3-20km/h
    • Roundup Ultramax 3-15km /h
    • Weedmaster DST 3-20km /h
    • Other Glyphosate products either have no label reference or are similar to the above statements
    • 2,4-D products 3 – 20km/h
    • Do Not spray when wind is below 3km/h
• Use of Adjuvants
  • • The use of Ammonium is critical:
      • It improves weed control regardless of water quality (plant uptake and movement)
      • It reduces glyphosate tie-up in hard water
    • Use an oil adjuvant such as Smart Penetrator when the weeds are predominantly broadleaf
    • Use a surfactant such as Smart 700 Spray
    • The use of a specialty adjuvant such as Wetter TX may be beneficial on ryegrass populations
• Boom setup
  • • Slow down
    • Reduce boom height
    • Apply with water volumes between 80-100L/ha
    • Minimum droplet spectrum;
      • Coarse for Glyphosate and Paraquat.
      • 2,4-D herbicides – No smaller than Very Coarse
•  Products
  • • Glyphosate forms the basis of most summer weed programs
    • Mixes with one or more of the following products is common. 2,4-D, Smart Triclopyr 600, Smart Fluroxypyr EC 200
    • Consider using Dropzone Herbicide rather than other 2,4-D products. Less odour, less risk with off target movement and improved control of some weeds.
    • Paraquat is an important product in summer, especially on hard to kill weeds in a double-knock program

What do you need to do?

1. Develop a summer weed control strategy with your Agronomist now
2. Plan your product requirements with us now to ensure you have access to what you need and when you need it

So, let’s develop a strategy together and tackle those summer weeds head-on! Your 2025 crops—and your profits—will thank you.

Key References:

1. 1. Hunt, J. (2011) Summer Fallow Management. GRDC. Available at: https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2011/02/summer-fallow-management
   2. Moore, A., & Hunt, J. (2012) Does control of summer fallow weeds improve whole-farm productivity in both Mediterranean and temperate environments? A simulation analysis, Australian Society of Agronomy. Available at: https://www.agronomyaustraliaproceedings.org/images/sampledata/2012/8145_5_moore.pdf
   3. Oliver, Y., Llewellyn, R., McBeath, T., War, A. & Moodie, M., (2023), Predicting profitability of summer weed control timing and impact on crop yield potential, GRDC. Available at: Predicting profitability of summer weed control timing and impact on crop yield potential – GRDC

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