Optimizing the application of plant growth regulators is one of the major technical challenges in modern blueberry production. Understanding how different variables—such as concentration, spray volume, pH, droplet size, and coverage—interact can make the difference between a successful application and an ineffective one, with direct economic costs for growers.
This will be one of the key topics addressed by Thomas Fichet, PhD in Biotechnology from the Polytechnic University of Valencia and lecturer in the Department of Agricultural Production at the Faculty of Agronomy, University of Chile, during the 2nd International Specialization Course in Blueberry Production, organized by Consultora Agrícola y Comercial Santa María (CASM Blueberries).
The event will take place from March 17 to 19, 2026, in Lima, Peru, and will include two technical sessions at the Sheraton Lima Hotel, as well as a Field Day at Qali Fruit, a subsidiary of Agrícola Cerro Prieto.
One of the main concepts Fichet aims to clarify is the difference between working with dose and working with concentration. “Many growers apply doses—defined as a quantity of active ingredient per hectare—but fail to consider that product concentration changes depending on the spray volume used. In contrast, concentration is fixed: it is a quantity per liter and does not vary with spray volume,” explains the specialist. For example, a dose of one liter per hectare will result in different concentrations if that hectare is sprayed with 1,000 liters of water versus 2,000 liters, directly affecting the performance of the molecule or active ingredient.
Another key aspect is understanding the difference between wetting and coverage. According to the expert, wetting refers to the volume of liquid applied to moisten a surface, whereas coverage refers to the uniformity with which the product reaches the different plant organs (leaves, fruit, and shoots).
“Improved coverage leads to greater efficacy, as plant growth regulators exhibit very limited mobility within the plant and their action is highly localized,” Fichet explained.
In addition, droplet size has a direct influence on absorption. “Smaller droplets dry more rapidly, reducing the time available for the product to penetrate the cell. Once the droplet dries, the product remains on the epidermis and can no longer enter the plant tissue, initiating a degradation process of the active ingredient.”
Water pH: A critical factor often overlooked
The specialist also highlighted the importance of the pH of the water used in spray applications. “Most plant growth regulators perform better under acidic conditions, with pH levels close to 5.5 or 6. However, applications are often carried out using alkaline water, with pH values ranging between 7.4 and 8, where the efficacy and penetration of many plant growth regulators are significantly reduced.”
During the course, trials evaluating different pH levels, various active molecules, and strategies to enhance active ingredient penetration will be reviewed.
According to Fichet, one of the major limitations of these products is their low penetration capacity. “Between 90% and 95% of the applied product never enters the fruit or leaf. Therefore, application efficiency is critical. In many cases, poor results are not due to the product itself, but rather to improper application practices.”
Common Field-Level Mistakes
Among the most common field-level mistakes identified, the specialist highlighted the following:
- Using low spray volumes per hectare in an attempt to reduce costs.
- Inadequate coverage of the target plant organ (leaf, fruit, or bud) intended to be stimulated.
- Use of water with unsuitable pH levels.
- Unrealistic expectations regarding the performance of certain molecules.
“Reducing spray volume to cut costs ultimately proves to be poor economics: if the desired effect is not achieved, the final cost is actually higher,” he emphasized.
Finally, Fichet stressed the importance for participants to understand that the application of plant growth regulators differs significantly from other foliar products such as mineral fertilizers. “Plant growth regulator applications have very specific characteristics. Understanding these differences is essential to achieve consistent and effective field results.”
Thomas Fichet will be among the featured speakers at the 2nd International Specialization Course in Blueberry Production ¡Secure your place at one of the most relevant technical events in the blueberry industry!
To purchase your ticket, please contact:
Agustina Martínez: +569 7934 1964
amartinez@casmblueberries.com
