Understanding Spray Adjuvants and Their Uses

Spray adjuvants are additives used in pesticide formulations or added to the spray tank to improve the biological performance or physical handling characteristics of the spray solution. The right adjuvant can significantly improve control, while the wrong one can reduce efficacy or cause crop damage.

Types of Adjuvants

Activator Adjuvants

These directly improve the biological activity of pesticides:

Non-Ionic Surfactants (NIS)

• •Reduce surface tension; improve spreading and penetration
• •Use rate: 0.1–0.5% v/v (100–500 mL/100 L water)
• •Best for: Postemergence herbicides, fungicides, insecticides on waxy leaves

Methylated Seed Oil (MSO) / Crop Oil Concentrate (COC)

• •Plant oil base; penetrates waxy cuticles effectively
• •Use rate: 0.5–1.0% v/v (500 mL–1 L/100 L water)
• •Best for: ACCase herbicides (fenoxaprop, fluazifop, quizalofop); postemergence herbicides on grasses

Silicone Surfactants (Organosilicones)

• •Super-spreaders; dramatically reduce contact angle
• •Use rate: 0.025–0.05% v/v (very low rate)
• •Best for: Systemic fungicides and insecticides; penetrating dense canopies

Utility Adjuvants

These improve the handling or storage characteristics of the spray:

Ammonium Sulphate (AMS)

• •Acidifies water; reduces antagonism from hard water cations
• •Use rate: 1–2% w/v (1–2 kg/100 L)
• •Essential with: Glyphosate in hard water areas

Anti-Drift Agents

• •Increase droplet size; reduce fine droplet drift
• •Use with: Phenoxy herbicides (2,4-D, dicamba) near sensitive crops

Stickers/Spreader-Stickers

• •Improve rainfastness; reduce wash-off
• •Use with: Protectant fungicides (mancozeb, copper, chlorothalonil) in areas with frequent rain

Adjuvant Selection Guide

Important Cautions

• •Always read the herbicide label — some products prohibit certain adjuvants
• •MSO/COC can cause crop burn in hot conditions — avoid applying when temperatures exceed 32°C
• •Silicone surfactants can increase herbicide uptake beyond intended levels — use at low rates
• •Never add adjuvants to fumigants or soil-applied products