Weed Control Methods Handbook: Tools ... - Invasive.org

Adjuvants 8.15
Foaming agents also act as drift control agents. When used with specialized nozzles, these
agents create foams with different degrees of stability (Witt 2001). These foams can be placed
more precisely than standard liquid sprays, and are sometimes used to mark the edge of spray
applications. Foams ensure complete coverage without over-spraying. Foaming agents are
usually added in quantities of 0.1 to 4.0% of the entire spray mixture (McWhorter 1982).
Thickening Agents
Thickening agents can modify the viscosity of spray solutions and are used to reduce drift,
particularly for aerial applications (Witt 2001). They are used primarily in agriculture.
Thickening agents may include water swellable polymers that can produce a “particulated
solution,” hydroxyethyl celluloses, and/or polysaccharide gums. Viscosity can also be increased
by making invert emulsions (follow directions on individual herbicide labels) of the spray
solution. The compatibility of the thickening agent with the tank mix can be influenced by the
order of mixing, pH, temperature, and/or the salt content of the tank solution. Thickening agents
are typically used in areas where sensitive populations or crops are growing close to treated areas
(McWhorter 1982).
Deposition Agents (Stickers)
Deposition agents, or stickers, are used to reduce losses of formulation from the target plants due
to the droplets evaporating from the target surface, or beading-up and falling off. Spray
retention on difficult-to-wet leaf surfaces is regulated by the degree of surface tension and
energy dissipation during the spray process. Deposition agents such as guar gum can reduce
surface tension while increasing the viscoelasticity of the droplets (Bergeron et al. 2000).
Stickers keep the herbicide in contact with plant tissues by remaining viscous, and therefore
resist being washed-off by rain or knocked off by physical contact. Stickers are generally the
most useful with dry wettable powder and granule formulations (Hazen 2000).
Film-forming vegetable gels, emulsifiable resins, emulsifiable mineral oils, vegetable oils,
waxes, and water-soluble polymers can all be used as stickers (Witt 2001). Fatty acids
(technically anionic surfactants) are frequently used as stickers, and although they are “naturally
derived” and are typically considered safe, they may have considerable contact activity. Certain
oils may also function as stickers, but only if they have a low degree of volatility (Hazen 2000).
Weed Control Methods Handbook, The Nature Conservancy, Tu et al.