Will the addition of spray additives (i.e., surfactants, crop oil concentrates, drift retardants, etc.) affect spray coverage and penetration?
Surfactants decrease the surface tension between the spray solution and the leaf surface and allow droplets to spread more evenly over the leaf. Therefore, coverage of individual leaflets that intercept droplets may increase. However, the addition of a spray additive does not necessarily result in increased coverage of the entire plant. Only by using 15 to 20 GPA spray volume and maintaining small- to medium-size droplets is coverage maximized. Spray additives may affect penetration via changing the spray droplet size. However, because of specific properties of individual fungicides and individual additives, the effect on droplet size cannot be generalized. The crop protection industry and universities are conducting research to clarify these chemical interactions. Consult individual product labels for compatibility issues and other factors that might alter fungicide efficacy.
