From rust to soybean anomaly: the evolution of diseases in the crop and appropriate management to minimize their losses

Asian rust is one of the main diseases that affect soybean crops in Brazil, mainly due to the difficulty in managing it. Its arrival in the country is quite recent, starting in the 2000s, definitively changing the routine of soybean farming, which began to adopt scheduled measures to manage and control the disease and led research and development companies to search for solutions that minimize the losses.

To understand a little the impact that rust had on soybeans, before it appeared, farmers invested around US＄ 5 per hectare to protect their plantations with chemical pesticides and, after its appearance, the value rose considerably, reaching an average from US＄25 to US＄30 per hectare, due to the violent negative impact on crop productivity.

Asian rust is the type of disease that can devastate up to 80% of a soybean crop and quickly became one of the main reasons for the drop in production in the country. Believe me, the negative financial impact caused by this disease exceeded R＄10 billion in a single year.

The situation became so critical that Brazilian farmers created special programs to deal with this threat. Brazil is a unique country in this sense, as it is the largest soybean producer in the world in a tropical climate. This means that rust has many chances to spread and transmute over time. To combat it, several strategies were adopted, from periods of sanitary emptiness to scheduled and preventive applications of pesticides.

But the story doesn't stop there. As soybean cultivation advanced to other areas and regions, new problems emerged, such as target spot, which has caused significant losses in plantations, especially in the Brazilian Cerrado. Controlling this disease requires the use of more complete products, with a broad spectrum of diseases.

White mold has also become a threat, especially in higher altitude regions. The problem is that the structures of this fungus remain in the soil for years, waiting for a suitable condition to develop in future harvests.

Recently, a new concern has emerged: the rotting of grains and pods during the filling phase, in soybean crops, known as soybean pod anomaly, mainly in the mid-northern region of Mato Grosso. Considering the potential area affected by the problem, as well as the average number of rotten grains obtained in Bayer's research trials, a loss of around R＄ 1,5 billion to the production sector in the last three harvests is estimated.

For this new challenge, the first measure recommended is the correct identification of the disease. The initial symptom is sometimes imperceptible, as the grains begin to rot inside the pods while they are still green, without external symptoms. Then, there is the appearance of yellowish-brown spots that evolve into pod rot and the premature detachment of the soybean seed from the pod coat. The problem is often confused with another soybean disease, anthracnose, as both affect the pod, but it is possible to differentiate by the darker tone that the latter leaves on the pod. Studies indicate that the choice of less susceptible cultivars and management with fungicides can help reduce losses.

But, over the years, all these diseases have accumulated in soybean crops, making managing these threats one of the biggest challenges for Brazilian farmers. 

Therefore, Bayer highlights some important measures to reduce the damage caused by these diseases:

1. Use the direct planting system with crops that help cover the soil with straw;
2. Respect the sanitary void period;
3. Within an agronomic limit, sow earlier to avoid the times most favorable to diseases;
4. Use chemicals preventively;
5. Choose effective chemical products, with assertive doses to control the main soybean diseases, such as Asian rust, target spot, white mold and grain rot;
6. Choose soybean varieties that have tolerance to some of these problems;
7. Implement the use of digital tools that contribute to effective monitoring and control in affected plots.

To maximize gains from soybean cultivation, the farmer must take management into account at the following times:

1. Vegetative application – its function is to reduce the initial pressure of diseases;
2. Pre-closing the line – most important application and, therefore, the most robust product must be applied, preferably more complete mixtures with highly efficient active ingredients. This pre-closure application must not be postponed due to the vegetative application;
3. Second application - must occur within 15 days after applying the pre-closing products. At this time, concern about rust and grain rot should be redoubled, giving preference to the use of products with a modern and efficient carboxamide;
4. Third and fourth applications - mixtures of triazole+strobirulins must be used, always accompanied by protective fungicides.

Finally, it is worth highlighting that the producer always seeks guidance from an agronomist to make the most appropriate decisions and monitor the work.

By Ronaldo Yugo (left), director of Bayer's Latam fungicide portfolio e Lucas Cardoso Santos (right), fungicide marketing manager at Bayer