What is spray quality?

Spray Quality refers to the optimal drop size of a pesticide when sprayed. Defined under a scheme introduced by the British Crop Protection Council to simplify and broaden the appeal of important application guidance, there are six sizes: 

• Very Fine - as in protected crop/greenhouse use; 
• Fine - for grass weed herbicides; 
• Medium - for systemic products and other herbicides; 
• Coarse - for soil applications; plus the more recently introduced 
• Very Coarse; and 
• Extra Coarse - for very low drift risk spraying.

A nozzle forms a thin sheet of spray liquid at its orifice which breaks down into drops. Drops produced by this 'sheet break up' method are not uniformly sized and are formed in a range of sizes. The average size of the drop will depend upon the size of the nozzle’s orifice, its design and spraying pressure . 

Different pesticides are now known to be more effective when applied in one size range or another so there is a need to communicate with operators which range is most appropriate for their spraying task. At first, nozzle sizes and designs were used for guidance and then an attempt was made to communicate mean drop sizes too, using numerical values.

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