hand, modern application equipment andapplication methods require emulsions <strong>of</strong><strong>the</strong> highest quality in order to allow <strong>the</strong>crop protection agent to be distributedevenly across <strong>the</strong> treated field. A fur<strong>the</strong>rconsideration is that <strong>the</strong> quality criteria for<strong>the</strong> registration <strong>of</strong> new products havebecome significantly more stringent.Careful with mixtures!All formulation types have to be testedfor <strong>the</strong>ir miscibility with o<strong>the</strong>r crop protectionproducts, fertilisers and additives,because <strong>the</strong>y must retain <strong>the</strong>ir biologicalactivity and crop compatibility in mixtureswith <strong>the</strong>se products. Each individual formulationis a finely-tuned „system“ initself. Mixing formulations in <strong>the</strong> spraytank inevitably leads to various degrees <strong>of</strong>unfavourable interaction between <strong>the</strong> inertingredients present in <strong>the</strong> different formulations.At worst, gel-formation, coagulationor sedimentation can make <strong>the</strong> spraymixture totally unusable. This places <strong>the</strong>onus on users to restrict <strong>the</strong>mselves to mixturesthat have been fully tested and validated.Soluble liquids (SL)The water-soluble, liquid concentrates(Soluble Liquids), like <strong>the</strong> EC and EW,contain <strong>the</strong> active substance in dissolvedformulations. Never<strong>the</strong>less, localized concentration<strong>of</strong> <strong>the</strong> product can lead to somedegree <strong>of</strong> crystallization if <strong>the</strong> spray mixtureis not properly stirred.Emulsions in Water (EW)EW-formulations are emulsions inwater. The emulsion can comprise a liquidactive substance, or o<strong>the</strong>rwise one that hasbeen dissolved in solvents. This means thatconsiderably less solvent is applied to <strong>the</strong>crop compared with EC-formulations.With an EW, <strong>the</strong> emulsion has already beenestablished in <strong>the</strong> sold product, and is onlydiluted in <strong>the</strong> spray mixture. EW-formulationshave <strong>the</strong> advantage that <strong>the</strong>y show littletendency to form crystals in <strong>the</strong> spraymixture. EWs can also be in <strong>the</strong> form <strong>of</strong>ei<strong>the</strong>r micro- and macro-emulsions.However, EW-formulations are uncommon,because few active substances areliquids or possess <strong>the</strong> suitable solubilityproperties.Suspension concentrates (SC)In SC-formulations, <strong>the</strong> active substanceis present as a solid that is finelydistributedin particles <strong>of</strong> between 1 and 4µm in size. The particles are held in suspensionin <strong>the</strong> water-based mediumthrough <strong>the</strong> addition <strong>of</strong> so-called dispersingagents; this effect involves mutualMixing a suspension concentrate (SC) with waterpresent as finely-distributed particles.means that its biological availability islower than with EC, EW and SL formulations.This is why SCs are most suitablewhen a high degree <strong>of</strong> contact exposure <strong>of</strong><strong>the</strong> host organism is <strong>the</strong> main aim.Water dispersible granules (WG)For insoluble active substances, wettablepowders (WP) used to be <strong>the</strong> preferredformulation type; however, <strong>the</strong>setend to form dust and are difficult to doseout. Nowadays, <strong>the</strong>se problems are solvedby choosing water dispersible granules.These are dust-free in practice, and allow<strong>the</strong> inclusion <strong>of</strong> large amounts <strong>of</strong> activesubstance in <strong>the</strong> product, so WGs are particularlyuseful for active substances thatneed to be applied at high rates. In thisway, even if production costs are relativelyhigh, <strong>the</strong> cost per hectare can usually bekept down. WGs generally show good cropcompatibility, so <strong>the</strong>y are <strong>of</strong>ten used formore sensitive crops, such as grapevine.Capsule suspensions (CS)Dissolving a soluble concentrate (SL) in water results in a clear solution.form. However, SLs differ from ECs andEWs in that every component <strong>of</strong> <strong>the</strong> formulationis dissolved in <strong>the</strong> water-basedspray mixture – which is why <strong>the</strong> latter isalways a clear solution. This means thatSL-formulations can only be developed foractive substances that are sufficientlywater-soluble. A minimum spray mixturevolume is usually recommended for SL-repellency between <strong>the</strong> particles; and incombination with o<strong>the</strong>r substances thatform net-like structures, <strong>the</strong> dispersingagents also prevent sediments from forming.One disadvantage though is that <strong>the</strong>product’s high viscosity generally makes itmore difficult to empty <strong>the</strong> packagingcompletely. The fact that <strong>the</strong> active substanceis present in crystalline form alsoCapsule Suspensions are <strong>the</strong> best choiceif an active substance shows problems withstability, or needs to be released in <strong>the</strong>environment in a controlled manner. Theactive substance can be present within <strong>the</strong>capsule ei<strong>the</strong>r dissolved or dispersed in <strong>the</strong>liquid phase. The internal phase <strong>of</strong> <strong>the</strong> capsuleis usually a solvent. The capsule ispresent in <strong>the</strong> product and later, in <strong>the</strong>spray mixture, in suspension. A CS ismade from an emulsion that already contains<strong>the</strong> active substance; <strong>the</strong> o<strong>the</strong>r componentis <strong>the</strong> capsule wall, <strong>the</strong> characteristics<strong>of</strong> which determine <strong>the</strong> release kinetics<strong>of</strong> <strong>the</strong> CS formulation.8 COURIER 1/05
produces a suspension. The active substance isSuspoemulsions (SE)A suspoemulsion is a combination <strong>of</strong> <strong>the</strong>SC and EW formulation types. The continuousphase comprises water, in which bothsolid particles and emulsion droplets arefinely distributed. This formulation type isespecially suitable wherever two activesubstances with starkly contrasting solubilitypr<strong>of</strong>iles or melting points need to bemixed. The emulsion phase can also containadditives that promote <strong>the</strong> systemicactivity <strong>of</strong> <strong>the</strong> active substance.Oil dispersions (OD)Many (new) systemic active substancescannot be formulated as ECs because <strong>of</strong><strong>the</strong>ir particular properties. Because <strong>the</strong>optimal activity <strong>of</strong> <strong>the</strong>se active substancesdepends on <strong>the</strong>ir entering <strong>the</strong> plant, alternativesare needed in which <strong>the</strong> active substanceis present in solid form. TheFormulation Technology Unit at BayerCropScience has developed various conceptsinvolving oil dispersions (OD) inorder to achieve <strong>the</strong> required levels <strong>of</strong> biologicalactivity and crop compatibility. Inan OD, a solid active substance is suspendedin an oil. The oil also serves as acarrier for additives and/or a safener.Diluting <strong>the</strong> OD in water can produce variousspray mixtures: if <strong>the</strong> active substanceis itself water-soluble (as in many herbicides),<strong>the</strong>n an emulsion results; if <strong>the</strong>active substance shows low water solubility(as in many insecticides), a suspoemulsionresults.OutlookIn <strong>the</strong> context <strong>of</strong> <strong>the</strong> steadily increasingdemands <strong>of</strong> modern crop protection, new,optimized variations on existing formulationtypes – and <strong>of</strong> course new concepts –Stirring water-dispersable granules (WG) into water makes <strong>the</strong>m spread spontaneously.will always be required. This is <strong>the</strong> taskassumed by <strong>the</strong> Formulation TechnologyUnit at Bayer CropScience. Formulationtechnology is an interdisciplinary scientificundertaking, with special relationships to<strong>the</strong> disciplines <strong>of</strong> colloid chemistry andinterfacial physics, in which technicalchemistry plays an essential role.In one <strong>of</strong> <strong>the</strong> next issues <strong>of</strong> Courier, youwill be able to read about how efficientmodern spray applications can be, and howformulation technology can improve <strong>the</strong>distribution <strong>of</strong> <strong>the</strong> active substances on,and within, <strong>the</strong> plant. ■Mixing an oil dispersion (OD) with water results in a suspoemulsion.1/05 COURIER 9
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