Simultaneously applying fungicide and fertilizer, a practice known as tank mixing, increases efficiency and reduces the time spent on plant care. This combined application involves mixing two chemically distinct products in a single sprayer, saving labor, decreasing fuel use, and reducing soil compaction. While combining these products is frequently possible, success depends entirely on the chemical and physical compatibility of the specific formulations. Failure to consider the interaction between the fungicide and the fertilizer can lead to poor results, equipment damage, or harm to the plants.
Chemical Compatibility and Stability
Mixing different chemical products into a single solution creates the potential for both physical and chemical incompatibility issues within the sprayer tank. Physical incompatibility occurs when components fail to mix uniformly, leading to separation, clumping, or the formation of sludge. This reaction, often called flocculation, can cause the spray mixture to settle out as a thick sediment at the bottom of the tank. This sediment obstructs nozzles and requires extensive equipment cleaning.
Chemical incompatibility is a more subtle problem that involves an undesirable reaction at the molecular level, often without immediate visible signs in the tank. The pH level of the final mixture is a primary factor, as many fungicides are stable only within a narrow pH range, typically between 5.0 and 7.0. Fertilizers, especially those containing nitrogen or phosphorus, can significantly alter the solution’s pH outside the optimal range. An alkaline pH (above 7.0) can cause alkaline hydrolysis, a process that rapidly degrades the fungicide’s active ingredient into an inactive form before it even reaches the plant. This degradation can render the application ineffective.
Consequences for Plant Health
Applying an incompatible or unstable tank mix can result in severe negative outcomes for the treated plants. The most immediate concern is phytotoxicity, which manifests as chemical burn, spotting, or tissue damage on the foliage. Mixing products can increase the concentration of salts and solvents, which, when sprayed onto the plant surface, can damage leaf cells. Certain fungicide formulations contain carriers or adjuvants that inadvertently increase the uptake of fertilizer salts to damaging levels.
When the fertilizer chemically degrades the fungicide, the primary goal of disease control is compromised. If the active ingredient breaks down in the spray tank, the application will fail to control the target fungus, wasting time and product. This reduced efficacy means the disease will continue to progress, requiring a new and often more expensive application later. Furthermore, an incompatible mix can introduce an imbalance in the plant’s nutritional status.
Applying too much of a specific nutrient, such as foliar nitrogen, while the plant is already stressed by a fungal infection can sometimes worsen the disease. High nitrogen levels can promote the growth of soft, succulent new tissue, which is often more susceptible to fungal pathogens. While a combined application is intended to treat two problems at once, an improper mix can lead to a complete failure of disease control and potential nutrient-related stress.
Necessary Precautions Before Application
Before attempting any tank mix, the first step is to consult the product labels for both the fungicide and the fertilizer. Federal regulations require that all pesticides be used according to their product labels. If a label explicitly prohibits mixing with other products, that instruction must be followed. Many commercial labels provide specific instructions or warnings regarding tank mixing, and some list compatibility with certain classes of fertilizers.
If the labels do not prohibit the combination, a small-scale compatibility test, known as a jar test, is mandatory. This test involves using a small, clean glass jar to mix proportional amounts of the water, fungicide, and fertilizer. After mixing, the solution should stand for 15 to 30 minutes to check for physical incompatibility signs, such as clumping, separation, or the formation of visible precipitates. Feeling the sides of the jar for warmth can also indicate an undesirable chemical reaction.
The order in which products are added to the water is also important to achieving a stable mix. A standardized mixing sequence is recommended, starting with products that are most difficult to dissolve or disperse. The typical mixing order is:
- Wettable powders and water-dispersible granules.
- Flowable liquids.
- Emulsifiable concentrates.
- Soluble liquids and fertilizers.
Adequate agitation must be maintained throughout the mixing process and the entire application to ensure the products remain uniformly suspended.