Can Fertilizers and Pesticides Be Mixed for Spraying?

Why Consider Tank Mixing?

Farmers often choose to tank mix for several practical reasons:

• Time Saving: Combining applications means fewer passes over the field, saving valuable time during critical growth stages.
• Labor Efficiency: Fewer spray operations reduce the labor required for mixing and application.
• Fuel Economy: Less time spent spraying directly translates to lower fuel consumption for tractors or sprayers.
• Reduced Soil Compaction: Fewer trips across the field can help minimize soil compaction, which is beneficial for soil health.

Key Considerations for Compatibility

Before mixing any products, always check for two main types of compatibility:

1. Chemical Compatibility

This refers to whether the active ingredients in the products react with each other. Incompatible chemicals can:

• Reduce the effectiveness of either the fertilizer or the pesticide.
• Form new compounds that are toxic to the crop (phytotoxicity).
• Become less stable or break down quickly.

Always read the product labels carefully. Labels often state if a product is incompatible with certain other chemicals or if it can be tank mixed.

2. Physical Compatibility

This refers to how well the products physically mix in the spray tank. Incompatible products might:

• Separate into layers.
• Form sludge, gels, or precipitates (solids).
• Cause foaming.
• Clog nozzles, filters, or pumps in the sprayer.

The Importance of a Jar Test

The most important step before tank mixing a large batch is to perform a small-scale jar test. This helps you check for both physical and chemical compatibility without risking your entire spray load or crop.

1. Take a clean glass jar (e.g., 1-liter capacity).
2. Add water in the same proportion as you would in your spray tank (e.g., if your sprayer holds 100 liters and you use 1 liter of product, add 10 ml of product to 1 liter of water in the jar).
3. Add each product in the correct mixing order (see table below), stirring well after each addition.
4. Observe the mixture for at least 30 minutes. Look for signs like separation, curdling, sludge formation, excessive foaming, or heat generation.
5. If the mixture looks good, spray a small amount on a few plants and observe for 24-48 hours for any signs of crop damage before applying to the whole field.

General Mixing Order (WALES Method)

Following a proper mixing order is crucial for good physical compatibility. A common guideline is the WALES method:

Order	Product Type	Description
1	Wettable Powders (WP) / Water-Dispersible Granules (WDG)	Add first, as they need time to fully disperse.
2	Agitate	Ensure continuous agitation throughout the mixing process.
3	Liquid Flowables (L, F, SC)	These are suspensions and should be added after powders.
4	Emulsifiable Concentrates (EC)	Oil-based products that form an emulsion in water.
5	Surfactants / Soluble Liquids (SL) / Foliar Fertilizers	Add last, as they help with spreading and absorption, or dissolve easily.

Best Practices for Safe Tank Mixing

• Always Read Labels: This is the golden rule. Product labels are your primary source of information on compatibility and mixing instructions.
• Perform a Jar Test: Never skip this step, especially with new combinations.
• Use Clean Water: Hard water or water with high pH can affect compatibility.
• Maintain Agitation: Keep the sprayer's agitator running continuously during mixing and spraying.
• Mix Just Before Spraying: Do not let mixtures sit overnight, as some products can degrade or separate.
• Wear Personal Protective Equipment (PPE): Always use gloves, masks, and protective clothing when handling chemicals.
• Clean Sprayer Thoroughly: After spraying, clean the tank, lines, and nozzles to prevent residue buildup and cross-contamination.

In summary, while tank mixing fertilizers and pesticides can be highly efficient, it is not a universally safe practice. Always prioritize safety and efficacy by carefully reading product labels, performing a jar test, and following the correct mixing order to ensure successful application and protect your crop.