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A formulation for every solution
Aug 03, 2018

I’ve been receiving a lot of questions lately about different formulation types and their advantages and disadvantages, so I thought I’d review this in this month’s column.

Crop protection chemicals rarely consist of just the pure active ingredient (AI). Instead, active ingredients are formulated in combination with other materials to improve handling, storage, in-paddock performance or safety of the product.

A soluble concentrate or liquid (SL) is where the AI is dissolved in water to give a concentrated solution. Unless the formulation contains a dye for safety reasons, SL’s are usually clear when added to the spray solution. They have advantages in that they are often easier to manufacture and have good dilution properties, although they may have lower temperature stability in the tank.

Emulsifiable concentrate’s (EC) are a blend of AI, solvent and surfactants. When EC’s are diluted into water, a spontaneous milky emulsion forms with dispersed, very small droplets. EC’s can be relatively cheap to make, tend to be physically stable and have good biological performance. However the solvents in them may be hazardous in their own right; some emulsifiers can increase crop phytotoxicity.

Wettable powders (WP) are a finely ground powder of the AI, most often combined with wetting agent, dispersing agent and inert filler. The general rule with WP’s is that the finer the particle size the better the product, because the particle must be dispersed in water and gravity wants to take it to the bottom of the tank. For convenience, WP’s often come in water soluble packaging to reduce dust and operator exposure. Here, you often get what you pay for and quality manufacturers focus attention on achieving micronized particle size. The advantage of WP’s is that they have high AI loading and they are generally lower cost to make. They do tend to exhibit less rainfastness, can be dusty and harder to get into solution. Don’t forget to use very good agitation in the spray tank with WP’s.

Suspension concentrate (SC) or flowable products combine many of the characteristics of EC’s and WP’s. The active ingredient is usually a solid that does not dissolve in water, so the powder is suspended in a small amount of liquid (usually water). Water-based SC’s often have better crop safety than EC’s, better user convenience, and the fine particle size gives good biological performance. While they are relatively cost effective to make they can suffer from physical stability issues (i.e. can settle out in the drum and spray tank).

Water-dispersible granules (WG/WDG) are solid, non-dusty granular formulations that re-disperse in water to a fine particle size suspension. Generally, these have good handling properties, high loading is possible, and spills can be contained easily. Often more expensive than WP’s, their dispersion properties can sometimes be an issue. Again, you’ll need good spray tank agitation.

Microencapsulated suspensions (CS) are an aqueous suspension of fine-size oil droplets containing the AI. The droplets are surface-coated with a solid polymer wall and the AI is released from dried spray deposit by wall rupture and diffusion.  Safety to the user, odour reduction, controlled or delayed release, reduced phytotoxicity to crops, the possibility of mixing otherwise incompatible active ingredients are all possible advantages with CS’s. Disadvantages can be changed biological performance and similar physical instability issues to SC’s. They’re often expensive to manufacture.

Oil dispersion (OD) is the other formulation worth mentioning. OD’s contain adjuvants in combination with an oil to improve retention, spreading and penetration. Generally, they have improved rainfastness, limited runoff, and improved efficacy, although they can be expensive to make, and the formulation may separate into layers in storage.