Tank mixing — combining two or more pesticides in a single spray application — can improve pest control efficacy, broaden the spectrum of activity, and reduce the number of field operations. However, incompatible combinations can cause product breakdown, crop injury, or dangerous chemical reactions.
Why Tank Mix?
- •Control multiple pests, diseases, or weeds in one pass
- •Broaden spectrum (e.g., fungicide + insecticide for disease AND pest control)
- •Herbicide combinations (pre-emergent) for grass + broadleaf coverage
- •Reduce the number of tractor passes through the field
- •Resistance management through mode-of-action diversification
Types of Compatibility Issues
Physical Incompatibility
Products that form lumps, separate, gel, or curdle in the tank. This can block nozzles and lead to uneven application.
Chemical Incompatibility
Products that react chemically with each other, leading to:
- •Breakdown of active ingredients (reduced efficacy)
- •Formation of phytotoxic compounds
- •pH changes that destabilise products
Biological Antagonism
Two products that individually give good control, but when combined, the total effect is less than either alone. For example, applying a fungicide that stresses the plant at the same time as a herbicide that requires active plant metabolism for efficacy.
Compatibility Testing (Jar Test)
Before mixing a full tank, always do a jar test:
- •Fill a clear jar with the intended water volume (use actual field water)
- •Add products in the correct mixing order at the intended rates
- •Mix well and observe immediately, then after 30 minutes
- •Look for: separation, flocculation (particles forming), gelling, excessive heat, colour change
- •If the mixture looks clean and homogeneous after 30 minutes, it is likely physically compatible
Correct Mixing Order (WALMIX)
Add products to the tank in this order:
- •Water (fill to ¾ level with pump/agitation running)
- •AMS / Ammonium sulphate (if used)
- •Liquid flowable suspensions (SC, CS formulations)
- •Miscible liquids / Soluble concentrates (SL, EC)
- •Intermediate: wettable powders (WP, WDG)
- •Xtras: adjuvants / surfactants (add last)
Special Considerations
- •Organophosphates + alkaline water: Organophosphates hydrolyse rapidly above pH 7. Always check water pH; add buffering agent if pH >7.5
- •Glyphosate + hard water: Hard water cations (Ca²⁺, Mg²⁺) antagonise glyphosate. Add AMS (ammonium sulphate) first
- •Herbicides + insecticides: Generally compatible but verify on label; some herbicides can increase crop uptake of insecticides
- •Copper fungicides + EC-formulated products: Can react; avoid unless label permits
- •Strobilurin fungicides + DMI fungicides: Usually compatible and synergistic — a common and recommended combination
Always Check the Labels
Some products specifically prohibit tank mixing with certain classes. Never assume compatibility — check both product labels, or contact the manufacturer's technical support.
