Miller, James H.; Manning, Steven T.; Enloe, Stephen F. 2010. A management guide for invasive plants in southern forests. Gen. Tech. Rep. SRS–131. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 120 p.
Adjuvants are any product other than water added to a spray solution to improve herbicide performance and effectiveness, including delivery, retention on foliage, and foliar or bark penetration. Adjuvants may be included as part of the commercial herbicide product or sold separately as an additive you must mix with the herbicide before application. Another common additive used by professionals is a marking dye, which is not an adjuvant. Choose an adjuvant according to label recommendations and appropriate for your particular application method and field conditions. Be aware that many adjuvants are sold under invalid claims and unproven results. Before purchasing an adjuvant, ask for recommendations from reliable, certified distributors, applicators, or extension specialists. Useful adjuvants and additives include the following and are classified here according to their type of action.
- Marking dyes and colorants
- used in selective or broadcast herbicide applications, verify that the treatment was applied to the intended target. Application dyes show how well target vegetation has been covered and whether harmful contact has been made with nontarget vegetation or with the applicator. Although dyes are messy and short-lived as visible markers, they are helpful in training applicators and checking the quality of applications. Common dyes include Bullseye® Blue Spray Pattern Indicator, Hi-Light® Blue Indicator, and Blazon® Blue Spray Pattern Indicator. Bullseye is a water-soluble polymeric colorant, not a dye, and nonstaining on skin, clothing, and equipment. Bas-Oil® Red is oil-soluble and used with basal oil mixes.
- Surface active agents (better known by the acronym surfactants)
- are a broad group of materials that facilitate the emulsifying, dispersing, spreading, wetting, and other surface modifying properties of liquids. Surfactants increase herbicide activity by making droplets larger on the leaf, thus improving penetration of the plant. Herbicide, weed species, and environmental conditions affect surfactant performance. Surfactants should be used with most foliar applications, except when prohibited by the herbicide label for specific uses, such as safety to desirable seeds and seedlings. Nonionic surfactants are usually recommended because they enhance wetting and retention of spray drops and do not bind with the herbicide molecule to cause deactivation. Never use household detergents as surfactants because they can deactivate many herbicides. Common surfactants include Entry II®, Big Sur 90, and Timbersurf 90. A newer type of surfactant with leaf penetrating action and rainfastness is based on organosilicones, with commonly used products being Sil Energy® and Silwet® L-77. These must be mixed exactly or they will be ineffective. They also increase the risk of injury to skin and eyes during application. Organosilicones are now commonly blended with other surfactants for additive properties.
- Water conditioners are spray solution additives
- that enhance herbicide performance by preventing deactivation of the herbicide’s active ingredient. Ammoniated salts are added to prevent loss of herbicidal activity of glyphosate and picloram when using “hard water” with greater than 200 parts per million of calcium, magnesium, and potassium. Acidifiers and buffers are additives sometimes listed on herbicide labels for use with specific water sources. Ammoniated salts, buffers, and surfactants are now blended to combine their activities in special spray additives. Common water conditioners are Choice® Weather Master, and AMSWC™ (just ammonium sulfate). Because dirt and organic debris can cause herbicide deactivation, always mix herbicides only with clean water from a filtered and treated source.
- Vegetable oils
- such as methylated seed oil (MSO), can increase spray drop adherence to leaves, increase herbicide penetration of leaves, and slow evaporation during and after application. Herbicides must remain in solution on a leaf for plant uptake. Vegetable oils also are mixed in basal sprays, and some vegetable oils contain emulsifying agents for this purpose. Several new formulations of herbicides come with vegetable oils. Common MSOs are Improved JLB Oil Plus and DYNE-AMIC®. A commonly used bark oil is Aqumix®.
- Drift retardants
- thicken spray solutions to create larger drops that are less likely to drift in wind, permitting more accurate applications in light wind and continued applications in slightly windier conditions. Common drift retardants are Poly Control 2, Nalcotrol®, and Sta-Put® Deposition Aid.
- Penetrants
- partially dissolve waxy plant surfaces to help the herbicide penetrate leaves or move through bark. Common penetrants are Cide-Kick® and Cide-Kick® II.
- Defoamers
- dissolve foam in spray tanks to improve mixing and transfers of herbicides like Arsenal AC and Velpar® L. Common defoamers are Fighter-F®10, Foam Fighter ®, and Brewer’s Defoamer.
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