EN 
PT_BR 
The boll weevil infestation reached its highest level in the monitoring series of the Mato Grosso Cotton Institute (IMAmt) in Mato Grosso during the 2025/26 crop season. The BAS index, which measures the average number of boll weevils captured per trap each week, increased from 4.61 in the 2024/25 season to 10.22 in the 2025/26 cycle.
The figures were presented this Tuesday (22), during the 15th Brazilian Cotton Congress (CBA), in Belo Horizonte (MG), by Márcio Souza, coordinator of Projects and Dissemination of Technologies at IMAmt.
Currently, the institute maintains a network of 864 traps distributed throughout the producing regions of Mato Grosso to monitor the pest population. According to Souza, the 2025/26 result was the highest in the historical series used by the institute, which began in the 2012/13 harvest.
The high pressure had already been observed during crop development. In March, IMAmt pointed to the 2025/26 season as having the highest boll weevil pressure in the last decade. With the closing of the harvest, the index confirmed a significant increase compared to the previous cycle.
Control begins before planting.
According to Souza, tackling the boll weevil requires actions that begin even before the new cotton crop is planted. The work involves complying with the sanitary break period, monitoring during the off-season, and eliminating volunteer plants, known as tigueras, which can maintain the pest in the system between cycles.
Another point highlighted by IMAmt is outside cultivated areas. Inadequate cargo handling and excess cotton in trucks can cause bolls to fall out during transport. These seeds can germinate on the roadside and give rise to volunteer plants that act as hosts for the boll weevil.
The institute also highlighted that monitoring and control actions are progressing toward the soybean growing season. In Mato Grosso, producers have been seeking strategies capable of addressing pests present in the oilseed crop and, at the same time, reducing boll weevil populations that remain in the system before cotton planting.
Managing volunteer soybean plants during the soybean growing cycle is also important for reducing so-called "green bridges," which allow the pest to survive between crops.
The year-round presence of host insects was also cited by Dyogo Fonseca, Market Development Manager at BASF Agricultural Solutions, as one of the factors that helps explain the increasing difficulty in controlling them. "Management of the boll weevil doesn't begin at harvest time."
According to Fonseca, the population observed during the off-season serves as an indicator of the pressure that may reach the following cycle. The presence of volunteer cotton keeps food and shelter available for the pest and reduces the population decline that would occur between harvests.
Another factor cited by the expert is the increase in irrigated systems in some producing regions. In his assessment, the presence of crops for longer periods of the year increases the formation of green bridges and favors the persistence of pests in the environment.
"In the past, we didn't have these green bridges so prevalent or so prominent in the area. So we were able to carry out a more limited and effective control," he stated.
With a larger population surviving between cycles, the cotton crop can begin development already under high boll weevil pressure.
Harvest 26/27 already begins with a warning.
The record set in 2025/26 once again places the boll weevil among the main phytosanitary challenges for the next season.
The discussion presented at the CBA reinforces that reducing cotton pressure for 2026/27 does not depend solely on applications made during cotton development. Management involves fallow periods, elimination of volunteer plants, off-season monitoring, careful transportation, and actions integrated into the soybean-cotton system.
Attention to logistics also plays a role in this process, since preventing the dispersal of seeds during transport reduces the possibility of the formation of new volunteer plants along the roads and, consequently, new survival points for the pest.
