Tank-mix compatibility
- Also known as
- tank mix, jar test, mixing order
Tank-mix compatibility is whether two or more crop inputs, such as pesticides, fertilizers, adjuvants and biologicals, can be combined in one spray tank without separating, forming solids, losing effectiveness or injuring the crop.
What is tank-mix compatibility?
Growers often combine several products in one spray tank to save trips across the field. That only works if the products are compatible. Tank-mix compatibility covers two kinds of problems.
Physical and chemical incompatibility
- Physical incompatibility shows up in the tank: products separate into layers, form gels, flakes or sludge, or foam excessively. These mixtures can clog screens and nozzles and give uneven application.
- Chemical incompatibility may not be visible. One product reduces the activity of another, called antagonism, or the combination injures the crop. A mixture can look fine and still perform poorly.
The jar test
Before mixing a new combination in a full tank, extension services recommend a jar test: combine the products in a clear jar in the same proportions and order as in the tank, using the same water, then shake and let it stand. Signs of physical incompatibility, such as separation, clumping or heat, indicate the mix should not be used as is. A jar test cannot detect chemical antagonism, which requires label guidance or field experience.
Mixing order
Product labels take priority. Where labels do not specify, extension guidance generally recommends filling the tank partway with water, starting agitation, and adding products in an order such as:
- Water conditioners and compatibility agents.
- Dry formulations, such as wettable powders and water-dispersible granules.
- Liquid flowables and suspensions.
- Emulsifiable concentrates.
- Solutions and soluble liquids.
- Adjuvants such as surfactants and oils, usually last.
Each product should be fully dispersed before the next is added.
What affects compatibility
- Water quality: hardness, pH and temperature.
- Formulation types of the products combined.
- Concentration and carrier volume.
- Time in the tank, since some mixtures degrade if left standing.
- Biologicals, whose living organisms can be harmed by some pesticides, fertilizers or adjuvants.
Frequently asked questions
A small-scale trial mix of the planned tank combination in a clear jar, used to check for physical incompatibility before mixing a full tank.
Adding surfactants and oils last helps the other products disperse properly first and reduces foaming during mixing, unless the label directs otherwise.
Sources
- Tank mixing and jar test guides, Land-grant university extension (e.g. Purdue University, North Dakota State University)
- Pesticide label directions for tank mixing, U.S. Environmental Protection Agency