Spray adjuvants are tank-mix additives used to modify and enhance the effectiveness of the pesticide. They can improve pesticide performance by modifying the spray pattern, quality, uptake and penetration into the plant or insect exoskeleton. Other benefits to adjuvants may include:

  • Keep pesticide from binding to minerals suspended in water.
  • Adjust water pH so pesticide is less likely to break down.
  • Manipulate droplet size to reduce on-target and off-site movement of pesticide.
  • Improve odds that a spray droplet will stay on the target by reducing factors that cause droplets to bounce and roll off.
  • Modify or reduce surface tension to enhance the ability of a droplet to be retained on or spread across the target surface.
  • Minimize spray droplet evaporation.
  • Prevent spray deposit from being washed off the leaf surface.
  • Protect the droplet from degrading in sunlight.
  • Improve pesticide’s absorption and uptake by the plant or insect exoskeleton.

Unless the product label specifies an adjuvant be added to the tank, growers do not need to use them. However, if use of an adjuvant is stated on the product label, pesticide performance and efficacy can be significantly reduced if it is not included. There are many types of adjuvants which include:

  • surfactants / wetter-spreaders (e.g., non-ionic surfactant, including organosilicones)
  • stickers / spreader-sticker (e.g., kaolin clay)
  • oil concentrates (e.g., petroleum-based crop oil, modified/methylated seed oils)
  • water conditioning agents • evaporation retardants
  • anti-foaming agents
  • pH adjusters (e.g., acidifiers, buffering agents)
  • drift suppressing agents

A label may specify a particular name brand or generalize a category of adjuvant. In the latter case, the grower is free to use any adjuvant in that category, provided it is registered for use on the crop and in combination with the pesticide being applied. Always use adjuvants as directed on the product label. For specific adjuvants, consult your local input retailer or product registrant.

General cautions around the use of adjuvants include:

  • Avoid the use of adjuvants that help with penetration into plant tissue with copper, sulphur or captan fungicides. This includes the use of oils. Penetrants should not be used with contact or surface pesticides.
  • Avoid adjuvants with sticker activity that could impede movement of systemic pesticides in plant tissue.
  • Avoid adjuvants with sticker activity early in the growing season when redistribution is important to protect newly emerging leaves. However, this may be a desirable characteristic during wet springs.

For more information on adjuvants, see the Sprayers 101 website at sprayers101.com.