Time to monitor diseases in soybeans

With the start of the soybean harvest, recommendation to producers: preventive and informed management is key to avoiding losses caused by diseases such as Asian rust.

Phytopathologist Marcelo Gripa Madalosso teaches that monitoring the property involves specific strategies for different types of diseases, considering regional risks and climatic conditions.

Monitoring and classification of diseases

Diseases that affect soybeans can be divided into two large groups: necrotrophic and biotrophic.

Necrotrophic diseases, such as those caused by fungi that remain in the soil or in crop residues, tend to worsen in monoculture systems due to the accumulation of inoculum in the environment.

Biotrophic ones, such as Asian rust and powdery mildew, are transported through the air and depend on specific climatic conditions to spread.

“It is essential for producers to know how to differentiate these groups and adapt their practices accordingly. Managing tolerant cultivars, monitoring climate conditions and consuming reliable information are essential points to minimize risks and maximize harvest results,” explains Madalosso.

Tools and the most common mistakes

Tools such as spore collectors are useful for identifying the movement of airborne pathogens, but should not be used as the sole trigger for fungicide applications.

“The mistake is to wait for the spore collector to signal the presence of pathogens before starting control. This can lead to delayed applications, especially in situations that favor rust,” explains the specialist.

The biggest mistakes producers make when controlling soybean diseases include:

• Delay the start of applications in conditions of high disease favorability.

• Maintaining long intervals between fungicide applications, especially longer than 14 days, which compromises preventive control.

• Exclusive dependence on a few chemical tools, without rotation of assets or adequate use of multi-site fungicides.

Climatic conditions and control challenges

Asian rust is highly dependent on leaf moisture for infection. Dewy, drizzled or light rain conditions create the ideal environment for its proliferation.

Climate monitoring must be aligned with management planning to avoid unpleasant surprises.

Furthermore, failures in equipment and application conditions compromise the results.

“The later the producer starts management, the more advanced the disease will be and the less effective chemical control will be,” highlights Madalosso.

Efficiency in management

To achieve good disease control, especially Asian rust, Madalosso recommends:

• Training and information: consume technical information and avoid unreliable sources.

• Regional planning: participate in monitoring programs, which provide an overview of the movement of spores in different regions.

• Suitable cultivars: choose varieties that are more tolerant to rust and adapt management to their characteristics.

• Crop rotation: avoid monoculture to reduce the pressure of necrotrophic diseases.

• Integrated management: combine chemical, cultural and climatic practices to achieve the best possible control.

Correct use of products

Another challenge highlighted by Madalosso is the gradual loss of effectiveness of available fungicides.

Many of these occur due to the inappropriate use of products and lack of rotation between chemical groups.

“We do not expect new chemical groups before 2027 or 2028. This means that current chemical management needs to be better planned, with preventive application and short intervals. We need to maintain the effectiveness of the products,” he warns.

Industry representatives agree. They explain that a lot of human effort and financial resources go into product development. But there is a minimum time frame to complete the process.

"In 2022, we launched the Revysol molecule (mefentrifluconazole) globally to control diseases in soybeans, corn, cotton and others. Later this decade, we plan to launch a new disruptive chemical group, specially developed for Brazilian soybean farmers. It is in our DNA to invest time, resources and create new molecules. However, producers need to adopt the necessary measures to maintain the effectiveness of the products available", explains Graciela Mognol, marketing director of BASF Agricultural Solutions in Brazil.

"The search for new chemical groups of fungicides is an ongoing challenge in the agricultural sector. Given the current challenge in disease management, all tools are important, as is the integration of chemicals and biologicals. An example of our commitment to innovation is Onsuva. It is essential that farmers use products as recommended, rotating chemical groups and active ingredients within the same chemical group," says Fábio Lemos, FMC's crop and portfolio manager.

Learn more about Asian rust in soybeans by clicking on:

• First cases of Asian rust were recorded in the 2024/25 harvest

• Efficacy of carboxamides in controlling Asian rust in soybeans

• Chemical control of Asian rust in soybeans

• Asian soybean rust genome directs new management strategies