Summer Fallow Weed Control

Rainfall Outlook, New Weeds

Version 2 Date January 2020 Reference 74

Key Points

Recent storm events in WA – have played havoc with harvest and also brought about a germination of weeds that will need to be controlled as soon as possible. The ability to “store” this summer rain, by controlling weeds presents an opportunity to set up the 2020 season – a strategy which has well proven yield advantages

Changing Rainfall Patterns

The recent rainfall events through Summer have become increasingly common over the past 10 years. This has re-inforced the shift from a predominant winter dominant Mediterranean climate to declining winter and increasing summer rain events (see figure 2).


Changing Weed Types

In the previous decade summer weed control used to focus almost exclusively on broadleaves like melons, caltrop and wireweed. “Tropical” type grasses such as button grass, windmill grass and kerosene grass were really only a problem in northern cropping areas – whilst broadleaves like fleabane and matricaria were rare – they are now becoming the dominant weed in much of the wheatbelt.

Figure 2: Self-Propelled boom spray. (Source: SACOA)

SACOA’s Research on Newly Emerging Fallow Weeds

Over the last five summers SACOA has built on it’s decades of research into making herbicides work more effectively, by focusing its field research program on new, difficult to control fallow weeds where matching the correct adjuvant to the most important herbicide mode of action in the tank  mix is critical. In addition, new herbicide mode of actions have also been evaluated, to ensure that growers are well informed on how to match the right adjuvant with the right herbicide mode of action. For example with some new actives such as Sharpen – the use of acidifying adjuvant such as a soyal phospholid can cause the herbicide to be inactivated.



Get the Most out of Summer Fallow Herbicides

Using an adjuvant that:

  • Increases droplet size – to reduce drift whilst still providing good coverage
  • Increases droplet survival – to allow herbicides to penetrate through leaves
  • Improves the mixing compatibility of multiple products in poor quality water
  • Is matched to the most important mode of action in the mix – generally targeted at the most dominant/difficult to kill weed in the paddock
  • Always add AMS to the mix particularly with glyphosate


Figure 1: Changing rainfall pattern 1910-2015.
(Source: David Stephens ‘South-west Western Australia is losing its Mediterranean Climate’ GRDC update 2016).

Lemons, Caltrip and Wireweed.

Figure 2: To Grass, Fleabane and Matricaria.
(Source: SACOA)


SACOA’s mineral oil based adjuvants ANTIEVAP® and ENHANCE® have become the fallow spraying adjuvants of choice in many cropping areas. In addition to the above benefits they also offer;

  • Flexibility to mix with all herbicides including glyphosate and paraquat for the double knock
  • Over twenty years of proven results under local Australian conditions
  • Ongoing product support including up to date information on new weeds and actives
  • Made in Australia, by a fully Australian owned, agriculture focused

The Facts

SACOA’s research program uses a combination of in-house and external resources to produce fully replicated and statistically sound information which is highly regarded in the industry for its integrity and relevance to current agronomic programs.

Results on Grasses

% Eragrostis Control – Quiarading

Chart 1: Eragrostis – Quairading (Source: T.Boyes AgVivo agronomy, Quairading


Button Grass Control – Mullewa

Chart 2: Button grass control – Mullewa (Source: SACOA/ADAMA/Elders -March 2017)


Windmill Grass Control – Mullewa

Chart 3: Windmill Grass Control – Mulle- wa (Source: SACOA/Elders/ADAMA – Mullewa April 2017)

Button Grass Control – Meckering

Chart 4: % Button Grass Control – Meckering (Source: T.Boyes AgVivo Agrono- my, Meckering)

Fleabane Control – York

Chart 5: Fleabane Control – York (Source: T.Boyes AgVivo Agronomy, York)


Fleabane Control – Quiarading

Chart 6: Fleabane Control – Quairading (Source: T.Boyes AgVivo Agronomy, Quairading)

Melon Control – Quiarading

Chart 6: Melon Control – Quairading (Source: T.Boyes AgVivo Agronomy, Quairading)

Matricaria Control – Wyalkatchem

Chart 7: Matricaria Control Wyalatchem (Source: SACOA internal trial Wyalkatchem)

Takeaway Messages

ENHANCE® and ANTIEVAP® proved superior to other adjuvant types, particularly soyal phospholipids and non-ionic surfactants across a range of broadleaf and grass weeds at multiple replicated trial sites. Improvement in performance was observed with all actives tested including glyphosate, paraquat, triclopyr, and GRP A

grass selectives with no evidence of compatibility issues or antagonism even on grasses. Clear rate responses between ENHANCE® 0.5% and ENHANCE® 1.0% were observed at all sites, with Glyphosate mixes being most rate responsive.

Importance of Correct Boomspray Setup

The final piece of summer fallow weed control is to ensure the herbicide mix goes out correctly. Summer spraying often produces some of the worst conditions for herbicides to work – therefore having the right nozzles, operating pressures, Delta T, travel speed & water volumes to minimise drift and maximise target coverage is critical to achieving the best results. Every boomspray and situation is different so use tools like water sensitive paper & snapcard (see figure 4) to ensure that herbicides get to where they need to be and always add AMS to every mix.


  • GRDC – Group A herbicides for control of grass weeds in fallow
  • Factsheets/2014/10/Group-A- Herbicides-in-Fallow