|Version 2||Date January 2020||Reference 16|
Recent rainfall across much of the western winter cropping areas, has resulted in good soil moisture profiles. As a result effective summer weed control programs will be essential to maintain yield.
Timing of application is critical for effective control and as most summer weed herbicides provide little residual activity, controlling later germinations depends on stopping seed set.
Whether you decide to spray early or late, adjuvant selection is critical to the performance of most active ingredients.
Adjuvants improve herbicide efficacy by reducing evaporation and drift, increasing droplet survival on leaf surfaces and increasing penetration of herbicide active ingredients into the plant.
Which of these is best suited to your needs depends on the active ingredient being used, the weed spectrum and stage, water volume, desired droplet size, spraying conditions and timing of the year, which may require the use of a particular type of adjuvant.
SACOA’s ANTIEVAP® is excellent at improving the efficacy of most summer fallow herbicides such as Triclopyr and/or Glyphosate.
An acidifying surfactant such as COHORT 700® may be of use as a buffering agent if water quality is poor, otherwise provides little benefit in improving droplet survival and penetration.
Droplet survival on the leaf surface is an important indicator of herbicide efficacy, and is influenced by three key factors
|Chart 1: Oil based adjuvants such as ANTIEVAP® have a positive effect on increasing droplet size versus non-ionic surfactants. (Source: USDA 2014)|
Adjuvants have an important role in improving herbicide efficacy by;
Oils and adjuvants can be split into two broad types – penetrants and spreaders.
Penetrants have properties which break down waxy leaf surfaces, allowing the active ingredient to enter the plant faster. They are generally plant or mineral oil based and due to their higher viscosity have the ability to increase droplet size or Volume Median Diameter (VMD) (see Chart 1).
Many grass selective herbicides such as the Group A’s are very poor on their own at entering leaf surfaces, particularly if they are waxy like ryegrass, but are translocated once inside the plant.
Hence most are labelled to be used in conjunction with an oil based penetrant adjuvant, where leaf surface coverage is not as critical as penetration.
Most spreading type adjuvants are surfactant based, which work by reducing the surface tension of liquids and thereby improve coverage on the leaf surface. Improved coverage is important for non-translocated herbicides such as paraquat, which work on contact and don’t need to enter through the leaf surface.
As a result of reduced surface tension, surfactants can decrease droplet size and increase drift. This may result in increased runoff of the active ingredient from the leaf surface, particularly fine leaf grasses, which may result in reduced efficacy (see Chart 1).
Role of Adjuvants in Melon Control
A 2012 trial conducted by AgSense at Goomalling examined the effect of time of day on herbicide efficacy and the efficacy of ANTIEVAP® , LI700 and ENHANCE® in some commonly used melon control mixtures.
The trial found;
• ANTIEVAP® and ENHANCE® proved superior to LI700 in Triclopyr & LVE mixtures.
• ENHANCE® proved superior to LI700 in Triclopyr, Glyphosate & LVE mixtures.
• Time of day did not affect the performance of ANTIEVAP® and LI700.
• The Untreated Control had >300 surviving melons 3WAA.
|Chart 2:ANTIEVAP® 1.0% and ENHANCE® 0.5% proved superior to LI700 with Triclopyr & Triclopyr + LVE mixtures. (Source: AgSense Western Australia 2012)|
Disclaimer and Copyright
This document should act as a guide only and no purchase or usage decisions should be made based on the information provided without obtaining independent, expert advice. SACOA and contributors do not necessarily recommend or endorse any products or manufacturers referred to. SACOA Pty Ltd will not be liable for any loss, damage, cost or expense incurred or arising by reason of any person using or relying on the information contained in this document. More information is available from SACOA via sacoa.com.au or 08 9386 7666, or by contacting your local reseller.
© 2020 SACOA Pty Ltd All Rights Reserved. SACOA and the GREEN S icon, ENHANCE, CROPSHIELD, PLANTOCROP, BIOPEST, XSEED, ANTIEVAP, STIFLE, SE14 and LURE H2O are registered trademarks of SACOA Pty Ltd.