New mutation increases Asian rust resistance to fungicides in Brazil

The fungus Phakopsora pachyrhizi is developing reduced sensitivity to fungicides from the triazole, strobilurin, and carboxamide groups, according to recent studies from reputable entities in the Brazilian agribusiness, including Embrapa Soja (Brazilian Agricultural Research Corporation).

Consultants and researchers have also identified new mutations of the causal agent of soybean rust in recent months, a scenario that raises concerns and has led to new official reports on effective disease control.

"Soybean rust arrived earlier in the 2023-2024 season, especially in the southern states, and a new mutation of the disease vector fungus could worsen resistance to certain fungicides," noted José de Freitas, agronomist in the Market Development area at Sipcam Nichino Brasil.

"This situation reinforced the need for producers to rotate active ingredients less vulnerable to resistance in preventive applications," he warned.

According to Freitas, entities such as the Antirust Consortium expected a high incidence of rust throughout the season "mainly due to delayed planting in various parts of the country compared to previous years, among other factors."

As per the agronomist, recommendations included rotating active ingredients of fungicides with different modes of action. It was also advisable to apply products preventively and with protective or multisite fungicides.

According to Freitas, the fungicide Fezan Gold (Tebuconazole + Chlorothalonil), distributed by Sipcam Nichino, was, at this point in the season, a "tailor-made solution for the producer."

He emphasized that the Antirust Consortium's Network Trials had evaluated the product for over six years.

"It has remained among the most effective cutting-edge solutions for disease control ever since," he pointed out.

According to the agronomist, from 2018 onwards, Fezan Gold has been among the top six most stable fungicides in controlling Asian rust, with an average performance indicator of around 65%.

"The fungicide's pioneering technology in the market combines systemic and protective properties with multisite action. Fezan Gold remains one of the few with such characteristics. Therefore, it continues to be strategic against rust and other diseases," he added.

Freitas revealed that in soybean areas affected by drought and extreme heat, there have been several cases of phytotoxicity in crops resulting from fungicide applications.

He also referred to a recent study by the MS Foundation, which assessed the negative impacts of phytotoxicity in fungicide applications under conditions of severe water deficit.

In response to this problem, "which leads to significant reductions in grain yield," Freitas said, the fungicide Fezan Gold also emerged as a suitable solution for the producer.

"The difference, in this case, lies in the water-based formulation of Sipcam Nichino's solution, whereas most fungicides that cause more phytotoxicity are oil-based or require this compound in the spray mixture," José de Freitas said in conclusion.

(Editing by Leonardo Gottems, reporter for AgroPages)