gChem Offers Top 3 Tips for Using Adjuvants
Agricultural adjuvants can be classified in several complementary ways: by the stage of the spray process they influence, by their functional purpose, or by their underlying chemistry. Process‑based categories include utility modifiers that improve formulation properties, spray modifiers that affect atomization and droplet formation, and activator adjuvants that enhance biological activity.
Functional classifications emphasize the specific role an adjuvant plays, such as stabilizing formulations, reducing foam, buffering pH, or modifying wetting, spreading, sticking, and drying behavior. Within these functional groups, wetter-spreader adjuvants reduce surface and dynamic surface tension to improve wetting, lower contact angle, and increase coverage; stickers enhance adhesion of dried deposits and reduce losses from wind, abrasion, or rainfall, particularly with wettable powders and dispersible granules; humectants slow droplet dry‑down to prolong liquid-phase activity; and penetration agents facilitate movement of active ingredients through natural barriers, improving uptake and bio-efficacy. Herbicide modifiers represent a distinct category that alters herbicidal activity through physiological mechanisms — such as safening or synergism — rather than through purely chemical or physical effects (Hazen, 2000; Spanoghe et al., 2007).
Dr. Darryl Ramoutar, Global Technical Director, Agriculture, gChem, discusses top three tips for using agricultural adjuvants.
1. Use Penetrants with Care
Penetrants enhance movement of active ingredients through natural barriers such as waxy cuticles, membranes, or insect integuments, but their effectiveness comes with important tradeoffs. Different penetrant chemistries act through different mechanisms. Surfactant-based systems may loosen cuticular waxes, oils may plasticize hydrophobic layers, and polar solvents can increase solubility and diffusion of actives. Because these mechanisms directly influence uptake rate and depth, penetrants can dramatically increase efficacy but also increase the risk of crop injury, especially under stress conditions or when used with herbicides that have narrow selectivity windows. Labels often specify when penetrants are allowed or prohibited, and those restrictions should be followed strictly. Polar solvents (e.g., alcohols, glycols, glycol ethers) are common penetrants because their mixed polarity allows them to interact with both hydrophilic and lipophilic components of the cuticle. They can accelerate uptake of systemic actives, but they also increase the chance of unintended absorption into sensitive tissues.
2. Consider Environmental Conditions
Environmental conditions often determine whether an adjuvant performs as intended. In hot, dry, low‑humidity environments, droplets evaporate rapidly, reducing coverage and uptake; humectants become valuable because they slow dry-down and extend the liquid phase, improving absorption of systemic actives. In windy conditions or when physical abrasion is likely, stickers help retain deposits after dry-down. When rain is forecast, stickers or polymer-containing can reduce washoff, while wetter spreaders alone may provide insufficient retention. Cold conditions can increase viscosity of oils and certain polymers, reducing atomization quality and producing overly large droplets. Even sunlight intensity matters: Rapid cuticle drying can reduce penetration, making humectants or certain surfactants more effective. The key is to treat adjuvant selection as an environmental decision as much as a chemical one, matching the adjuvant’s mechanism to the weather, crop condition, and application window ensures consistent, predictable performance.
3. Think About Droplet Size and Drone Applications
Adjuvants can significantly alter droplet size distribution, and this matters because droplet spectra determine drift potential, canopy penetration, and deposition efficiency. Surfactant-heavy wetter spreaders often reduce surface tension enough to produce finer droplets, increasing coverage but also elevating drift risk if not paired with appropriate nozzles or pressures. Conversely, oils, polymers, and certain utility modifiers can increase viscosity or alter breakup dynamics, producing larger droplets that reduce drift but may compromise coverage on dense or hydrophobic foliage. These dynamics become even more important in drone applications, where rotor wash, flight height, and forward speed interact with droplet formation under your nozzle and pressure conditions. Drones typically operate with lower spray volumes and smaller droplets, making them more sensitive to adjuvants that reduce dynamic surface tension and create ultra-fine droplets prone to drift. The practical takeaway is that adjuvants, nozzle type, and drone flight parameters must be treated holistically.