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Early Post-em Weed Control

In this month’s agronomy article we look at the importance of using the correct spray quality, or droplet size, when applying herbicides as well as early herbicide timings.


Spray Quality

We often think about droplet spectrum and drift in fallow spraying but we want to assure you that it is important all year-round.  Farmers and the environment benefit from applying herbicides with the correct spray quality or droplet size for several reasons:

  1. Minimising Drift: Herbicide drift can harm neighbouring crops. Using an optimum droplet size helps minimize drift potential and keeps the products in your paddock and on your target. If you think that finer droplets lead to better coverage, you may be wrong. Smaller droplets often don’t reach the target.
  2. Precision Application: Correct and Precise droplet sizes ensure better weed control which can help to minimise input and operational costs.
  3. Spray Coverage: Larger droplets ensure that more product actually reaches the intended target. This can provide better coverage and weed control. Very small droplets (<150 microns) are prone to drift and should be avoided.

By understanding and implementing the correct droplet size, farmers can enhance herbicide effectiveness and reduce negative impacts on crops and the environment.

To achieve better results:

  1. Slow down
  2. Lower the boom height
  3. Use the correct spray quality
  4. Use the correct adjuvants

Note: If you increase the droplet size you will need to increase your spray application volume.

Listed below are a selection (not all) of the products that are registered (on the label) to be used with a COARSE or larger droplet spectrum

  • Arcade (Smart Silver)
  • Balance (Smart Soxx 750)
  • Boxer Gold
  • Glyphosate (all formulations)
  • Lontrel (Smart Clopyralid)
  • LVE MCPA (Smart MCPA LVE 570 EC)
  • MCPA 750 (Smart MCPA Amine 750)
  • Paradigm
  • Priority (Smart Florasulam 200 WG)
  • Terbyne Extreme (Smart Terbuthylazine 875WG)


Early herbicide Timings

In some regions, it is proving difficult to apply herbicides due to staggered or split germination of crops.

You may often experience a staggered germination and when we discuss early timings we will be referring to the leaf stage present in the majority of the crop. Please consult the label and with your agronomist to ensure you are applying the herbicides within the correct application window.

In 2024, Canola has been prone to staggered germination. In canola, herbicide timing can be a tight window as we attempt to apply most herbicides before the 6-8 leaf stage or prior to bolting. Grass herbicides such as Smart Target 200 (Quizalofop) and Smart Clethodim 240EC can be applied from Cotyledon stage. Factor can be applied from the 4-leaf stage but please refer to your agronomist for specific application guidelines to minimise the effect on crops.

Tenet 500SC is registered from the true 1 leaf stage of canola and you should wait for the crop to be at this stage before spraying.

Roundup Ready Herbicide with Plantshield can be applied from crop emergence to Roundup Ready canola and Truflex Roundup Ready canola. Roundup Ready Herbicide is registered to be applied with Clopyralid 300g/L from crop emergence.

Smart Terbuthylazine 875WG can be applied from crop emergence.

The labels state that Atrazine in TT canola and Smart Commandeer (Imazamox/Imazapyr) in Clearfield canola can be applied from the 2-leaf stage.

Liberty Link canola has registration for Liberty Herbicide from the 2-leaf stage of the crop.

Optimum Gly Canola label states to apply Glyphosate from the cotyledon stage (cotyledon fully unfolded).

A conversation with your agronomist to discuss early applications of herbicides is essential. It is a complex situation and often involves compromises.

Follow the label and consult with your Agronomist on adjuvant use and spray application setting to apply the products with the correct droplet spectrum (spray quality).



Lastly, remember that it is important to read the herbicide label on the containers carefully. There are many products with similar actives, similar names and similar looking containers in the market.

There is an old carpentry quote – “measure twice and cut once“. We should remember to check twice before we take action with Ag Chem products.

If you have any questions or if there is anything we can assist with please reach out to your local Crop Smart representative.


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