The size of the spray particle is important because it affects both efficacy and spray drift of the application of an herbicide, insecticide, or fungicide. If the size of the spray particle (for example, 250–500 microns) is doubled and the application volume stays the same, you have only one-eighth as many spray droplets (Figure 1). For example, to gain optimum efficacy in weed control, a 10–20 gallons per acre (GPA) spray volume is typically recommended, with a “medium” droplet size suggested for contact nontranslocating herbicides, and a “coarse” droplet size suggested for contact translocating herbicides. Concern for drift may cause you to consider using larger droplet sizes and higher spray volumes.