Rain increases reports of Asian soybean rust in the 22/23 harvest

As in previous harvests, the month of January has seen a rapid increase in reports of Asian rust in soybean-producing states and municipalities. According to a survey by the Antirust Consortium, in the 2022/23 harvest, there are 119 reports of the disease and rust is present in nine Brazilian states, with 79% of occurrences in commercial crops in the grain filling phase. At the same time, last harvest, there were 59 reports, however, the climatic conditions were different - lower rainfall in the southern region of the country, Mato Grosso do Sul and Paraguay - which reduced the occurrence of the disease. Researcher Cláudia Godoy, from Embrapa Soja, explains that rust is favored by the well-distributed rain throughout this harvest.

“In regions where rainfall is regular, the disease is more common when fungicide applications fail or the fungicides used have low efficiency in controlling rust”, explains Godoy.

According to the National Supply Company (Conab), more than 50% of crops are in the grain filling phase (after R5), a situation where the disease causes less damage. Godoy states that the potential for damage from Asian rust is greater in crops still in the vegetative stage, flowering and pod formation, which receive a greater quantity of fungus inoculum from areas sown earlier. 

“If conditions remain favorable for the disease, the most delayed crops will require applications with highly efficient fungicides to control the disease”, he warns. “Even the most efficient products for control must be associated with the use of multisite fungicides, as the rust inoculum increases in the regions”, she comments.

The comparison of the efficiency of registered fungicides and those in the registration phase for the control of Asian rust has been carried out in network experiments, carried out since the 2003/2004 harvest, in Brazil. Fungicides are evaluated individually, in sequential applications, in late sowings, to determine control efficiency.

Reports about rust outbreaks have already made the news on the Revista Cultivar website. Read more at: Spots of rust in the south of Mato Grosso raise alert.

Other soybean diseases in the 22/23 harvest

The Embrapa researcher also reports the occurrence of other diseases in this harvest. In the Cerrado regions, for example, where there has been a good distribution of rainfall in the initial sowings, a high incidence of target spot has been observed. Furthermore, in the South region, there are reports of white mold in higher regions with milder temperatures and in periods of lower rainfall the presence of powdery mildew.