other additives for farm chemicals Revised 2012 edition
Caution: Research on Unregistered Pesticide Use Any research with unregistered pesticides or of unregistered products reported in this document does not constitute a recommendation for that particular use by the authors or the authors’ organisations. All pesticide applications must accord with the currently registered label for that particular pesticide, crop, pest and region. Disclaimer Any recommendations, suggestions or opinions contained in this publication do not necessarily represent the policy or views of the Grains Research and Development Corporation (GRDC), Conservation Farmers Inc. No person should act on the basis of the contents of this publication without first obtaining specific, independent professional advice. The Corporation and contributors to this booklet may identify products by proprietary or trade names to help readers identify particular types of products. We do not endorse or recommend the products of any manufacturer referred to. Other products may perform as well as or better than those specifically referred to. The GRDC and Conservation Farmers Inc. 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 in this publication.
Title: Adjuvants – Oils, surfactants and other additives for farm chemicals – revised 2012 edition
Authors: Compiled by agricultural consultant Andrew Somervaille, with assistance from Graham Betts (specialist spray consultant), Bill Gordon (Bill Gordon Consulting), Vicki Green and Michael Burgis (Conservation Farmers Inc) and Rosemary Henderson (Protech Consulting).
Project Coordinator: Lloyd O’Connell, Australian Grain
GRDC Project Code: BER00009
©2012 Grains Research & Development Corporation Published December 2011 ISBN: 978-1-921779-32-9 In submitting this report, the authors have agreed to the GRDC publishing the material in its edited form.
Copies of this publication are available at $10 per copy plus postage and handling from:
Ground Cover Direct Free Phone: 1800 11 00 44 Email: [email protected]
For further information contact: Ms Maureen Cribb GRDC Publishing Manager PO Box 5367 KINGSTON ACT 2604 Phone: 02 6166 4500 Email: [email protected]
ADJUVANTS – Oils, surfactants and other additives for farm chemicals | 1
Contents Foreword 3
Chapter1–Adjuvantsbackground 4 Whatareadjuvants?4 Classificationofadjuvants 4 Howdoadjuvantswork?4 tosumup6
Chapter2–Majoradjuvantgroups 7 surfactants7 oils9 Acidifiersandbuffers10 Fertiliseradjuvants11 others11 tosumup12
Chapter3–Adjuvantsforherbicides 13 GroupAherbicides 13 GroupBherbicides 14 GroupCherbicides 16 GroupFherbicides 16 GroupGherbicides 18 GroupHherbicides 18 GroupIherbicides 19 GroupJherbicides 20 GroupLherbicides20 GroupMherbicides(glyphosate)21 Groupnherbicides22 GroupQherbicides22 GroupRherbicides23 GroupZherbicides23 specialnotesonnon-selectiveherbicidesandadjuvants23 Waterqualityandeffectiveherbicideapplications24 Readyreckoners25
Chapter4–Adjuvantsforinsecticides 26 Carbamates(Group1A)26 organophosphateinsecticides(Group1B)26 Phenylpyrazoles(Group2B)27 syntheticpyrethroidsandpyrethrins(Group3A)27 nicotinyls(Group4A)28 spinosyns(Group5)28 Avermectins(Group6)28 nonspecificmodeofaction–selectivefeedingblockers(Group9B)29 Mitegrowthinhibitors(Group10Aand10B)29 Biologicalinsecticides(Group11)29 DisruptorsofAtPformation(Group12)30 Pyrroles(Group13)30 Moultingaccelerators(Group18)30 oxadiazines(Group22A)30 Ryanodinereceptormodulators(Group28)31 Insecticidesofunknownmodeofaction31 others31
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Chapter5–Adjuvantsforfungicides 32 Group1fungicides(benzimidazoles)32 Group2fungicides(dicarboximides)32 Group3fungicides(demethylationinhibitors–DMI:imidazoles,azoles,piperazineandpyrimidines)33 Group4fungicides(acylalanines,oxazolidinones)34 Group9fungicides(anilinopyrimidines)34 Group11fungicides(strobilurins)34 Group33fungicides(phosphonates)34 Group40fungicides(carboxylicacidamides)35 GroupMfungicides(multi-siteactivitygroup)35 Fungicidegroupswithnorequirementforadjuvants37 top10tipsforeffectivefungicidespraying38
Chapter8–Waterqualityandyoursprayproduct 41 Mixingorder42 examplesofpesticideseffectedbywaterquality43
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FoReWoRD ANNUAl worldwide spray adjuvant sales are currently estimated to be worth more than $1.5 billion. In Australia alone, over 300 branded products are currently registered for use as spray adjuvants, surfactants or wetting agents and these products have more than 30 different ‘active ingredients’ providing different functions for enhanced pesticide or nutrient efficacy.
The Australian adjuvant market continues to expand with a plethora of new products offering improved performances of herbicides, fungicides, insecticides, foliar nutrients, defoliants and conditioners.
But there is a limited, and sometimes outdated understanding of how to get the most out of the right adjuvants for different spraying jobs. This revised edition of Adjuvants – Oils, surfactants and other additives for farm chemicals addresses this often complex area.
The Grains Research and Development Corporation (GRDC) and Conservation Farmers Inc (CFI) have produced this revised publication with the aim of equipping consultants, agronomists and farmers with a greater understanding of adjuvant attributes and their properties.
This often complex subject is clearly explained with the use of easy to follow charts, tables and tools such as ‘ready reckoners’, a Q&A section and a glossary of technical terms.
The GRDC and CFI would like to acknowledge the expert assistance of agricultural consultants Andrew Somervaille, Graham Betts, Bill Gordon, Vicki Green and Rosemary Henderson in the revision of this publication.
Michael Burgis John Harvey Executive Officer Managing Director Conservation Farmers Inc (CFI) Grains Research and Queensland Development Corporation Phone 07 4638 5355 www.grdc.com.au Email [email protected]
4 | ADJUVANTS – Oils, surfactants and other additives for farm chemicals
ANNUAl worldwide spray adjuvant sales are currently estimated to be worth more than $1.5 billion. A large part of this estimate represents the value of adjuvants built into pesticide formulations. But many millions of dollars are also spent on stand-alone products retailed as adjuvants, surfactants and wetting agents.
In Australia over 300 branded products are currently registered for use as spray adjuvants (142), surfactants (44) or wetting agents (120). These include about 30 different ‘active ingredients’ some of which are combined in individual products to provide different functions.
While there are many adjuvants available for use with farm chemicals, a much smaller number of products are recommended by the manufacturers or distributors of farm chemicals.
This can cause some confusion particularly where there are a large number of branded products providing identical – or near to – active constituents.
Adjuvants are used in a variety of farm chemicals, including herbicides, fungicides, insecticides and growth regulator products.
In recent years, the major growth area in the use of adjuvants has been with herbicides. There has been an economic incentive to optimise effectiveness, under a wide range of conditions, of the more expensive herbicides.
Whatareadjuvants? An adjuvant is any material that when added to a spray solution
enhances or modifies the action of a pesticide. Many adjuvants are included (or ‘factory-fitted’) in the formulations of various products to facilitate the stability and functionality of the active ingredient(s) in a spray solution.
But farmers are keenly interested in those adjuvants that can be added to the spray solution on-farm to help get the most out of their dollars spent on spraying programs.
Classificationofadjuvants The most useful classification of adjuvants is by chemical
group with the adjuvants divided into the broad categories of surfactants, oils, acidifiers and buffers, fertiliser adjuvants and ‘others’.
An alternative classification can be made on the basis of spray adjuvant function. This can be confusing since some adjuvants may have more than one function (for example, spreader and buffer).
Howdoadjuvantswork? Adjuvants work at three levels in the application of farm
i. Modifying how chemical components or products interact in the spray tank
The two most common adjuvant products at this level are compatibility agents and drift retardants.
Compatibility agents are usually surfactants that enable active and inert materials to co-exist in a stable solution. These products are normally factory fitted into the formulation.
They are particularly important in formulations where the active ingredient is insoluble in water.
In other formulations where the active ingredient is relatively insoluble, the active may be formulated as a suspension or dry flowable concentrate. Here surfactants are used to ensure that the product is stable in the concentrate form but readily disperses on dilution in water.
Figure 1a: How oil and water based solutions can be made to mix using adjuvants
There are a number of drift retardant products, which when combined with pesticides, alter the surface tension properties of the solution. In this process the atomisation of spray droplets may be modified.
Adjuvant products which increase the surface tension of solutions will tend to reduce the atomisation of sprays which alters the spectrum of spray droplets formed.
A coarser spray can be achieved by increasing the viscosity of the spray mix. This results in an upward shift of the droplet spectrum to reduce driftable ‘fines’.
Many spray adjuvants can be added to a tank mix to increase its viscosity. There are a number of drift retardant products commercially available and they are normally some type of long chain polymer or gum that increases the viscosity of the spray mixture.
Some US research (Ozkan et al., 1992) tested five drift retardant chemicals to determine their effects on droplet size, spray pattern, and spray drift reduction. All five retardants reduced the portion of small droplets (less than 100 microns) in the spray volume but to varying degrees. The most effective retardant had 68% less droplets under 100 microns while the least effective had 30% less.
Some studies have found that some of these polymers tend to be sheared by passing through a sprayer pump, as would occur in normal bypass, or hydraulic mixing in common agricultural sprayers (Zhu et al., 1997). Gums are not sheared as
GlOSSARY OF TERMS
tohelpunderstandthetermsusedindescribingthe typesandfunctionsofsprayadjuvants,aglossaryof termsanddefinitions,basedonstandardterminology relatingtoagriculturaltankmixadjuvantsdeveloped bytheAmericansocietyfortestingofMaterials,is providedonpage46
ADJUVANTS – Oils, surfactants and other additives for farm chemicals | 5
easily as the long chain polymers, and some types of polymers (poly-ethylene oxide) are sheared in fewer passes through a pump than other types of polymers (polyacrylamides).
Although drift retardants are generally effective in reducing the number of driftable fines, in most cases users are better off using the appropriate nozzle, operating the sprayer at low pressure to obtain the desired droplet size and spraying when the environmental conditions are right.
Some adjuvants by their nature increase atomisation, e.g. surfactants, which reduce surface tension, and increase the tendency of droplets to break up in the process of atomisation.
This property varies with different surfactants and concentrations so that there may be an apparent variation in the tendency of a spray solution to ‘drift’ under a given set of conditions, depending on the surfactant type and the concentration present in the spray solution.
Adjuvants may modify the evaporation of spray droplets as they are released. As droplets containing surface active agents (surfactants) or oils are released into the atmosphere, evaporation of the spray droplet continues until the surface tension of the droplet ‘skin’ prevents further evaporation.
Medium and large size droplets are more likely to reach the target under the influence of their own weight by ‘sedimentation’ compared to droplets that are initially very small (or evaporate to a size) which makes them more vulnerable to the influence of air movement.
ii. Modifying how a product interacts with the target surface
The most common way of modifying the interaction of spray droplets and the target surface is by altering the surface tension of the droplet.
Droplets with a high surface tension will be more likely to bounce off target surfaces while those with a low surface tension will tend to spread on contact and be retained.
A spray solution with spherical shaped droplets on contact with a surface are said to have a high surface tension. Droplets that readily deform and spread on contact have a lower surface tension (Figure 1b).
Surfactant adjuvant molecules move between water molecules forcing them further apart. Surfactants lower the surface tension of the spray droplet by moving to the surface where they form a ‘micelle’ layer.
Surface tension decreases until the surfactant concentration reaches a point known as the Critical Micelle Concentration (CMC). At this point, addition of more surfactant does not decrease surface tension though enhancement of pesticides generally (particularly herbicides) may continue.
Reducing surface tension to as low a level as possible may not always be beneficial. Droplets may run off the target surface as droplets coalesce (due to very low surface tension or where a high volume application causes droplets to run together). Some surfactants may reduce surface tension to the point that the spray deposit dries too quickly, reducing uptake of an active ingredient that needs to be in a semi-liquid state to be absorbed.
As well as affecting droplet spread, surface tension can influence the formation of spray droplets, rate of evaporation and retention on sprayed surfaces.
Droplets with a high surface tension will be more likely to bounce off target surfaces while those with a low surface tension will tend to spread on contact and be retained.
Figure 1c: Contact angle of droplet on a difficult-to-wet leaf surface without (a) and with (b) surfactants
(Source: Devine et al., 1993 adapted by Hall, 1999)
Dynamic surface tension is the measure of how quickly surfactants migrate to the surface of the droplet at the point of impact. Unlike static surface tension (measured after a spray droplet has been deposited on a surface for a period of time), dynamic surface tension can decrease at concentrations greater than the CMC.
Recent evidence has shown that the effects of adjuvants on post-emergent herbicide performance are due more to dynamic surface tension than static surface tension. Retention of sprayed solutions on a target is usually at an optimum at levels well above the CMC, particularly if the surface is hairy.
Decreasing the surface tension of a solution will result in a decrease in the size of spray droplets produced by an atomiser. While this may increase potential for spray drift, retention on leaf
Figure 1b: Using high speed photography, various droplet formation patterns depending on nozzle type, spray pressure and spray mixture are illustrated
6 | ADJUVANTS – Oils, surfactants and other additives for farm chemicals
surfaces (particularly on narrow, upright leaves of small grasses) is improved since the impact energy of droplets is lowered.
Decreased surface tension and increased spreading does not always equate to improved herbicide performance. The opposite trend (improved weed control with reduced droplet spreading) has been demonstrated with glyphosate, imazethapyr (Spinnaker®), nicosulfuron (Accent), primisulfuron-methyl and thifensulfuron-methyl (Harmony® M).
iii. Modifying how a product moves into the target pest
Uptake of pesticides across a target surface is a complex process, often involving more than one pathway. With the herbicide glyphosate, some movement of the active ingredient is due to a simple process of diffusion across the leaf cuticle. Uptake in this situation appears to be improved when the spray deposit is retained in a semi-liquid state increasing the continuity of uptake.
With some plants, glyphosate may also enter the plant through the stomata. This is enhanced by some surfactants which reduce dynamic surface tension to a sufficiently low level. Uptake across the cell wall and plasmalemma (cell membrane) may also be facilitated by an electrochemical transport system.
Adjuvants may also affect the uptake of pesticides across a plant or insect cuticle, physically disrupting the surface by dissolving waxy deposits. This cuticle-disrupting property of some adjuvants may cause the pesticide to be less effective or it may heighten the injury to the target crop directly or indirectly by reducing the selectivity of the applied pesticide.
Certain crop oils, when exposed to heat or ultra-violet light on leaf surfaces, cause disruption to cell membranes resulting in phytotoxicity to crop plants.
Figure 1c: Cross section of a leaf surface with spray droplet on surface. The waxy surface acts as a barrier to water droplets
(Source: Rochecouste, 2004)
tosumup Adjuvants are products added to a spray solution that
enhance or modify the action of a pesticide.
Adjuvants can be classified according to their function or chemical grouping.
Adjuvants can have a variety of functions such as spreading, wetting and/or modifying droplet formation and behaviour.
While there are many types and functions of spray adjuvants, they can be conveniently categorised as surfactants, oils, acidifiers/buffers and fertiliser adjuvants.
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surfactants SURFACTANTS make up by far the largest group of spray
adjuvants. In agricultural applications, non-ionic (having no net electrical charge) surfactants (NIS) make up the majority of products although a number of formulations utilise anionic surfactants to assist in dispersibility of formulations in a dry form.
Another group occasionally represented as agricultural surfactants include the cationics (with a net positive electrical charge).
Surfactants act as wetting or spreading agents and their main role is to act on the surface of a droplet to reduce the surface tension. This allows the droplet to spread over the leaf surface.
Field experiments from 2002–06 demonstrated a more reliable control of diamondback moth (DBM) in brassicas when surfactants are added to the insecticide mix. The non-ionic surfactant Agral®, when added to Altacor® and Couragen® insecticides, gave consistently better control of DBM than when these insecticides were applied without the surfactant.
Table 2a lists a number of common agricultural surfactants by chemical type.
Surfactants are made up of two functional parts – a hydrophilic or ‘water loving’ structure attached to a lipophilic or ‘fat loving’ component (see Figure 2b).
The hydrophilic-lipophilic balance (HlB) of a surfactant is a measure of the relative contribution of the hydrophilic and
Alcohol alkoxylates Alkylaryl ethoxylates Fatty amine ethoxylates
Organo-silicones Other products with more than one active constituentNonyl phenol Octyl phenol
di-1–pmenthene(egnu-Film-P®, Hyper-stik,sprayfast,Flextend,shur-stik, Flexstic,Hygro-stic)
oxiwet®,kendeen20,PomadeWetting Agent(Polyoxyethylenesorbitan monolaurate
Primabuff®,Bladbuff,Aquabuff,Quatrabuff (nonylphenolethoxylate+phosphoricacid derivatives)
8 | ADJUVANTS – Oils, surfactants and other additives for farm chemicals
lipophilic component. It can have a distinct influence on the performance of adjuvants with different pesticides. Both the type and size of the hydrophilic and lipophilic portions of a surfactant may influence droplet spread, droplet bounce, evaporation and pesticide absorption.
Figure 2a: Interaction of hydrophilic and lipophilic parts of a surfactant to reduce surface tension and spread the droplet
(Source: Hall et al, 1999)
Surfactants are classified on the basis of the electrical charge carried by the hydrophilic group. Surfactants are anionic (negative charge), cationic (positive charge), amphoteric (carry both positive and negative charge) or non-ionic (no charge).
Examples of various hydrophilic groups utilised in various surfactant groups is summarised in Table 2b.
Table 2b: Surfactant types according to electrical charge on the hydrophilic group Surfactant type
Charge on hydrophilic group
lipophilic (‘fat loving’) groups are derived from natural or petrochemical feedstocks and include:
Alkylphenyls e.g. Nonylphenol
Traditionally, most agricultural surfactants are non-ionic with a hydrocarbon base comprising the lipophilic component of fatty alcohols, alkylphenols, fatty amine or sorbitan esters attached to an ethylene oxide chain of varying length. In recent years, surfactants based on silicone (organosilicones) e.g. Pulse®, have been developed with agricultural applications.
Alternatively, anionic (negatively charged compounds) may be attached to the lipophilic part or directly to the hydrophilic part of the molecule to provide a specialised function, either as part of a formulation (to provide emulsification or dispersion of the active ingredient) or as adjuvants in their own right.
Anionic compounds are mainly phosphate esters (used in buffering agents), sulfates, sulfonates and carboxylates.
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oils(table2c) Oils were used for insect and weed control as well as anti-
microbial agents before the development of synthetic pesticides.
As adjuvants, oils are used to:
Enhance the penetration of systemic pesticides into plants and insects;
Reduce evaporation of spray droplets after they leave the sprayer; and,
Extend the active life of certain herbicides, insecticides and fungicides on plant surfaces.
In ultra low volume (UlV) spray applications, petroleum oils are used as bulking agents. Oils can be categorised on the basis of their origin (vegetable or petroleum base) and their formulation.
Petroleum based oils can be subdivided into those with low (1–3%), medium (5%) and high (>15%) levels of added surfactant/emulsifier (petroleum spray oils, petroleum oil/ surfactant blends and petroleum spray oil concentrate).
The type and amount of surfactant used in a petroleum spray oil product can have a major effect on performance.
Petroleum oils vary in base oil composition, paraffin content and the amount of unsulfonatable residue. These properties influence viscosity and phytotoxicity. Some petroleum spray oils, e.g. Canopy®, contain additional UV stabilisers which provide a degree of UV protection for pesticides.
Vegetable oils are usually emulsified and may be categorised according to their crop origin. In addition, plant-based oils may be esterified as well as emulsified (see Table 2c) to give…