Darryl Ramoutar, Ph.D., Global Technical Director, Agriculture, gChem.

Tank mixing pesticides with other liquid products — such as biologicals, fertilizers, and plant amendments — is a widely used practice in modern agriculture. It offers clear advantages by saving time and reducing application costs, allowing growers to manage multiple pests while delivering nutrients in a single spray pass (OSU, 2026).

However, integrating biologicals (including microbial inoculants and biopesticides) into these mixtures introduces important viability risks. When combined with conventional formulations and adjuvants (such as stickers, spreaders, and penetrants), biological products may experience reduced fitness, and formulations may exhibit chemical incompatibility (e.g., flocculation or clogging), or even phytotoxicity (crop injury) (TAMU, 2026).

A major concern lies in so-called “inert” ingredients — such as surfactants, solvents, and fragrances for example — either present in formulations or added to the tank. Despite being labeled inert, many of these compounds can exert antimicrobial effects and unintentionally sterilize beneficial microbes. Research also shows that pesticide exposure can shift soil microbiomes: fungi tend to be more sensitive than bacteria, herbicides and fungicides cause stronger off-target impacts than insecticides, and repeated applications can significantly alter fungal diversity and community composition (Riedo et al., 2025).

Darryl Ramoutar, Ph.D., Global Technical Director, Agriculture, gChem, provides advice to help ensure inert safety to microbes in biopesticides and the soil microbiome.

1. Carefully Select Surfactants

Surfactants are a key class of adjuvants that can strongly impact microbial survival. These compounds can solubilize and lyse microbial lipid membranes, resulting in broad-spectrum antimicrobial activity against both bacteria and fungi (Falk, 2019; Hoefler et al., 2012; Sharma et al., 2021). Certain surfactants — including cyclic lipopeptides and cationic agents — can also damage fungal spores by degrading structural components of the cell wall, causing deformation and rupture. At concentrations as low as 0.5–2.0%, these effects can disrupt protective spore layers, inhibit germination, and lead to leakage of intracellular contents (Forsyth, 2011). Surfactants may also interfere with microbial ecology by preventing biofilm formation. By altering surface properties and reducing hydrophobic interactions, they inhibit microbial adhesion, the critical first step in establishing beneficial microbial communities.

In soil and root environments, microbes commonly form biofilms: protective, self-produced matrices that attach to soil particles and plant roots. These biofilms are essential to soil health, helping stabilize soil structure, retain moisture, and support nutrient cycling (Musa, 2015; Cai, 2019). On plant roots, biofilms in the rhizosphere act as a functional interface between plants and microbes. They enhance nutrient uptake, support root development, and protect plants from pathogens and environmental stresses (Rafique, 2024; Bhattacharyya, 2024). Biofilms can even produce their own biosurfactants, which aid in microbial communication and adaptation (Jimoh, 2023). Because surfactants disrupt adhesion and weaken extracellular matrices, they can compromise these beneficial biofilms, potentially reducing the effectiveness of microbial inoculants.

Selecting surfactants for pesticide tank mixes that include biologicals requires balancing performance with microbial safety. Nonionic surfactants, such as alcohol ethoxylates, alkylphenol ethoxylates, alkyl polyglucosides, and sorbitan esters, are generally preferred because they provide effective wetting, spreading, emulsification, and penetration enhancement while being less disruptive to microbial membranes than cationic or strongly antimicrobial chemistries. Some of these are also biobased and compatible with common systemic herbicides, insecticides, and fungicides. With careful selection, surfactants can preserve microbial viability while still delivering effective spray performance.

2. Choose The Right Solvent

Solvents, another common component of agricultural formulations, affect microbes differently but still pose risks. Many solvents partition into microbial membranes, altering their structure and function. This can lead to increased membrane fluidity or rigidity, leakage of cellular contents, and eventual cell death.

Beyond membrane effects, solvents can destabilize proteins and enzymes, disrupt metabolic pathways, and interfere with cellular energy production. These stresses force microbes into survival mode, reducing growth, metabolic activity, and overall performance (Segura, 2012; Tan, 2018; Torres, 2011).

Compared to surfactants, solvents may have a less pronounced impact on overall soil microbial diversity, with some studies showing limited effects on community structure (Riedo et al., 2025). The best solvents for tank mixing with microbial products are water-dominant systems with mild, biodegradable co-solvents (plant oils or glycols), while harsh organic and highly polar solvents should be minimized due to their strong antimicrobial effects. However, toxicity varies widely by solvent type; for example, dimethyl sulfoxide (DMSO) is generally less harmful to biopesticides than more aggressive polar solvents like NMP and NBP (gChem, 2026), when working with hard to dissolve active ingredients.

3. Adhere to Best Practices

While tank mixing can be efficient and beneficial when done correctly, it requires careful management to protect living microbial inputs. Best practices include:

• Strict adherence to product label directions
• Avoiding incompatible chemistries and harmful ingredients (e.g., copper, oxidizers, peracetic acid, fungicides, bactericides)
• Managing spray solution pH (generally below 9)
• Ensuring sanitized equipment before introducing biologicals
• Alternating applications when compatibility is uncertain

Preserving microbial viability — the ability of biological agents to remain alive and functional — is essential for achieving consistent performance in the field. When these organisms are compromised, the effectiveness of biological products is significantly reduced, undermining their intended benefits.