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Populations of the caterpillar (Rachiplusia naked) and armpit borer have shown resistance to Cry1Ac (first generation Bt soybeans), a problem that has worsened in this 21/22 harvest. Despite this negative news, it is important to highlight that this should not impact the performance of Bt soybean technology for the management of other species targeted by the technology, such as the false caterpillar (Crysodeixis includens) and the soybean caterpillar. Despite these resistant populations, it is important to highlight that the use of insecticides to control them should only be done when population levels reach action levels.
For Embrapa Soja researcher, Adeney de Freitas Bueno, “the producer must be cautious when verifying the need for control, respecting the MIP-Soja recommendations, which indicate the correct time to apply insecticides”. Bueno also reinforces that Bt plants are just one component of management strategies, and MIP-Soja recommends the association of different sustainable tools.
Embrapa has identified the indiscriminate use of insecticides in an attempt to control these caterpillars. Studies indicate that insecticides against defoliating caterpillars should only be applied when defoliation is equal to or greater than 30% during the vegetative stage of soybeans or 15% during the reproductive stage. Before this moment, insecticides are unnecessary and their application, in addition to increasing production costs, eliminates beneficial insects that are responsible for keeping other pests in balance.
Although the causes of the resistance of Rachiplusia nu and the armpit borer to Cry1Ac (Bt soybeans) are complex, researchers from Embrapa Soja emphasize that the low adoption of structured refuge areas is a factor responsible for the greater occurrence of these insects in soybeans. Bt. “We observed a reduction in the adoption of structured refuge in soybean cultivation. Thus, in a scenario of high adoption of Bt-soy technology and low adherence to the practice of structured refuge, the probability of resistance evolution in the target species increases considerably”, highlights Bueno. The researcher warns that it is essential to plant at least 20% of structured refuge (non-Bt soybeans), sown so that the distance between a Bt plant and a non-Bt plant is within a maximum of 800 m.
The adoption of the refuge area and the rational use of insecticides, among other MIP-Soja recommendations, are important for the sustainability of Bt technology. More detailed information is available at technical note on the Embrapa Soja website, which talks about the “Occurrence of Rachiplusia nu and Crocidosema aporema in Bt soybeans in the 20/21 harvest and main management guidelines for producers for the 21/22 harvest”.
This topic will be the topic of the “Especial Safra” on the CBSoja GoLive platform, on February 16, 2022, and will also be discussed at the IX CBSoja and Mercosoja 2022, which will be held in Foz do Iguaçu (PR) between May 16 and 19, 2022. .
Two strategies are essential so that this problem does not worsen in this and other harvests.
1) Application of insecticides at the right time: The indiscriminate use of insecticides in an attempt to control these caterpillars worsens the problem of resistance. Studies indicate that insecticides against defoliating caterpillars should only be applied when defoliation is equal to or greater than 30% during the vegetative stage of soybeans or 15% during the reproductive stage. See the publication at the end of the email. Before this moment, insecticides are unnecessary and their application, in addition to increasing production costs, eliminates beneficial insects that are responsible for keeping other pests in balance.
2) Use of structured refuge: The low adoption of structured refuge areas is a factor responsible for the greater occurrence of these insects in Bt soybeans. The essential thing is to plant at least 20% of structured refuge (non-Bt soybeans), sown so that the distance between a Bt plant and a non-Bt plant is within a maximum of 800 meters. See below the diagram of the refuge area in soybean crops.
1. To register for events, access the website www.cbsoja.com.br.
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