Adjuvants have been developed to improve spray dispersion, reduce volatility, spray drift, and foaming, improve plant penetration, buffer spray solution, plus other functions. The most commonly used adjuvants are non-ionic surfactants.
Surfactants reduce surface tension of spray droplets which allows better plant coverage.
Without surfactants, droplets roll off hard to wet plant surfaces. Some fungicide formulations contain compounds that act as surfactants. In these cases manufacturers may not suggest a surfactant be added to the spray mixture. In other cases, and in particular with wettable powders, labels may emphasize the need for a surfactant to enhance effectiveness. If a chemical label does not specify the use of an adjuvant, one should realize that he assumes the risk of undesirable results if any should occur.