Revised information on spray adjuvants for fruit crops

Here is a guide to the wide assortment of additives sold to growers for improving spray applications to their fruit crops.

This is a revision of the adjuvant section of the 2010 Michigan Fruit Management Guide, Michigan State University Extension Bulletin E-154.

Spray adjuvants are products added to a spray tank to improve the performance of the treatment. Improper use of an adjuvant may result in poorer performance and possible phytotoxicity as well as increasing the cost of the treatment. An adjuvant may not be needed in some cases. Many agrichemical products are formulated with adjuvants and may not need an additional one. In some cases, the use of adjuvants is specifically prohibited. Check the agrichemical label to see what type of adjuvant, if any, is recommended. Check the adjuvant label to be sure that the target crop and the intended use are listed.

Avoid use of adjuvants with penetrating action with potentially phytotoxic fungicides. For example, do not use an adjuvant with strong penetrating action with copper compounds, Captan or Syllit. Be aware that soluble fertilizers may also have penetrant activity and can help move the copper or Captan into the plant tissue. Be careful when using adjuvants with penetrating action with herbicides that may come in contact with young tree trunks, vines and canes.

Emulsifiable concentrate agrichemicals contain oil and special adjuvants to allow them to mix with water. These emulsifiable concentrates will sometimes help other normally non-systemic agrichemicals to penetrate into plant tissue.

Systemic fungicides and insecticides are designed to move into plant tissue. With such agrichemicals it is best not to use an adjuvant with aggressive “sticking” action that would impede movement into plant tissue.

Avoid adjuvants with strong sticking action early in the growing season when redistribution of fungicides and insecticides by rain is desirable to extend protection to newly emerged green tissue. However, sticker action may be desirable under extended rain and cool conditions.

General terminology

Spreader: Also called surfactants, wetting agents, surface-active agents. An adjuvant with spreader activity helps to decrease water surface tension, encouraging spray droplets to land and spread over hard-to-wet surfaces such as waxy and/or hairy plants. A detergent can act as a spreader to prevent beading. Too much spreader can result in increased spray treatment dripping off of treated surfaces.

Non-ionic spreader: A surfactant with spreading action and relatively neutral charge. For general use, non-ionic spreaders are usually preferred over negatively charged (anion) and positively charged (cation) spreaders because non-ionic types are least likely to inactivate the chemicals being applied.

Penetrant: An adjuvant that enhances the movement of the agrichemical into the plant tissue. Penetrants may also help penetrate the cuticles of arthropods. Penetrants are used with many herbicides and defoliants and certain fungicides and insecticides. Many penetrants also act as spreaders and surfactants. Use penetrants with caution – they can cause phytotoxicity by helping to move non-systemic materials such as copper and Captan inside the plant cuticle. Penetrants should not be used with materials that should stay on the surface. Penetrants are not recommended on certain crops, such as grapes, where they may increase risk of damage to tender skin. Common penetrants include oils and methylated or ethylated oils, ethylenes, alcohols and aliphatic acids.

Sticker: Also called bonder. It is an adjuvant that enhances the adherence of agrichemicals to the target surface. Sticker activity is generally more useful for non-systemic agrichemicals than for systemic agrichemicals that work best inside plant tissue. Stickers are helpful for fungicide or insecticide products that are prone to wash-off, including biocontrol products. High rates of some stickers can immobilize agrichemicals. High rates of some stickers can result in excessive foaming and or result in a tenacious film on equipment. Latex-based stickers usually need to dry on plant surface before they provide protection. Terpene-based stickers (Nu-film products) need sunlight to set the film.

pH modification agents and buffers: An acidifier helps to reduce water pH. A buffer helps the spray solution to be stable at a specific pH, usually acidic. Buffers and acidifiers help guard against unwanted agrichemical breakdown, clumping and other effects that may occur because groundwater sources are often alkaline (high pH) in Michigan. Most agrichemicals are most stable at slightly less than neutral pH (below 7). Materials with a significantly shorter life at high pH include Captan and Imidan.

Drift retardant: An adjuvant that helps to inhibit the production of fine droplets by spray nozzles. It’s usually used to help prevent off-target movement of herbicides or other potentially damaging agrichemicals.

Water conditioner: An adjuvant providing some benefit in the spray tank, such as protecting against negative effects of some water sources. An example is ammonium sulfate, which helps to prevent inactivation of glyphosate by tying up calcium, magnesium and iron in hard water that would otherwise bind to the herbicide. Ammonium sulfate replacements are available from several companies.

Foam retardant: This is commonly a dimethylpolysiloxane product that helps to suppress excessive foam in the spray tank that results from agitation of other materials and water. It works better if added to the spray tank before excessive foaming occurs rather than afterward.

Compatibility agent: This is useful when pesticides are combined with liquid fertilizers to help avoid breakdown of the pesticide by the salt solution from the fertilizer. Some troublesome combinations of products can be stabilized with a compatibility agent.

Silicon-based adjuvant: Reduces surface tension (aids wetting). Higher rates result in more penetration. These adjuvants are recommended for use with water-soluble pesticides only. This class of adjuvant contains some of the more aggressive penetrants.

Crop oil concentrate: An adjuvant that is a combination of surfactants (15 to 20 percent) and non-phytotoxic oil, either petroleum- or vegetable-based. Crop oil concentrates are used to increase effectiveness of herbicides by increasing wetting, spreading and penetration. Methylated seed oils tend to work better than petroleum-based oils as adjuvants for weed control where weeds are under environmental stress.

View table of products and descriptions.