Researchers monitor weed resistance to herbicides in Mato Grosso

Free online platform helps producers better plan control strategies

13.06.2023 | 14:37 (UTC -3)
Embrapa
With the free platform, producers can plan weed control strategies; Photo: Julio Bogiani
With the free platform, producers can plan weed control strategies; Photo: Julio Bogiani

Embrapa researchers are monitoring the occurrence of herbicide-resistant weeds in Mato Grosso. The work, carried out in conjunction with Bayer, is part of a national effort bringing together a large team of experts across the country and can be seen at an online platform open access. On the website, it is possible to check the points where seeds of biotypes suspected of resistance were collected, the species and which herbicide and mechanism of action the plants are resistant to.

“The idea is that the website serves as a warning to producers. When they see that there is resistance in their region, they can plan control strategies, whether by rotating molecules and mechanisms of action, using pre-emergent herbicides, for example, or even cultural management using cover crops. ”, explains the researcher at Embrapa Agrossilvopastoril, Fernanda Ikeda.

The work

The identification of resistant populations begins with field collections, in expeditions carried out to the main agricultural areas of the state, where seeds of escape plants suspected of resistance are collected. Seeds may also be sent by producers and consultants who find populations suspected of resistance 

Collected or received, the seeds are sown in pots in a greenhouse. The plants go through an initial evaluation process, in which they are exposed to the recommended doses of the herbicides selected for testing each species in the ideal application phase and conditions. Those individuals that survive control are previously classified as resistant. It is this data that is released on the platform.

“Not all plants that survive in crop areas are resistant. Survival is often due to various factors such as application at a lower dose than recommended, application with the plant stressed or at an advanced stage, product mix, lack of adjustment on the sprayer, wind during application, among others. Therefore, many of the samples collected end up proving susceptible in this first test”, explains researcher at Embrapa Algodão Sidnei Cavalieri.

To reach a definitive diagnosis of resistance, it is necessary to assess whether the resistance characteristic is hereditary, that is, whether it is passed on to subsequent generations. Furthermore, there may be different levels of resistance, which are identified in dose-response curve studies using increasing doses of the herbicide and with repetitions. 

Dose-response curve tests are also being carried out at Embrapa Agrossilvopastoril, but as they take longer, it was initially decided to launch the platform with data from the first evaluation in a greenhouse.

“This is already an important indication for the producer. He can see what the situation is like in his region, whether there is resistance selection pressure for any product or mechanism of action and can use this information in decision making”, explains Cavalieri.

The expectation is that the platform will be updated little by little with new samples collected and tested. In the future, information proving resistance should also be included.

How to collaborate by sending seeds

Producers, consultants and farm managers who find weeds with suspected resistance can contribute to the research by sending seeds to be tested at Embrapa.

Samples should preferably be from just one plant, with a greater number of seeds. The history of herbicide application in the area and the geographic coordinates of the collection point must also be sent.

Shipping must be made to Embrapa Agrossilvopastoril, under the care of Fernanda Ikeda. The address is Rodovia MT 222, km 2,5, Zona Rural, Sinop (MT). PO Box 343. CEP 78.550-970.

Results from Mato Grosso

Seed collections in Mato Grosso were concentrated in 2018, 2019 and 2021. Three species with the greatest economic impact in the state were prioritized: crow's foot grass (Eleusine indica), sour grass (Digitaria insularis) and horseweed (Conyza spp .).

To date, 196 crow's foot grass biotypes have been evaluated, with 24% classified as susceptible to all herbicides, 54% as resistant to one or more ACCase inhibitors (clethodim, fenoxaprop-p-ethyl and haloxyfop-p -methyl), 5% resistant to glyphosate (EPSPs inhibitor) and around 17% resistant to one or more ACCase inhibitors and glyphosate.

“We saw that 70% of the samples had some indication of resistance to herbicides from the chemical group of aryloxyphenoxypropionates (FOPs), while only 13% had resistance to clethodim alone or combined with other FOP(s) and/or glyphosate”, highlights Ikeda.

For bittergrass, 116 biotypes were evaluated. Around 69% were classified as susceptible to all herbicides, 22% resistant to glyphosate and 8% as resistant to one or more ACCase inhibitors (the majority classified as resistant to haloxyfop) and glyphosate.

Horseweed, which, like bittergrass, is dispersed by the wind, resulted in only 19 biotypes. Larger numbers were evaluated, but the lack of seed germination limited the data. Of the biotypes analyzed, 21% were susceptible to all herbicides tested (2,4-D, chlorimuron-ethyl, diquat, ammonium-glufosinate, glyphosate and saflufenacil), 42% resistant to glyphosate and 37% with resistance to chlorimuron and one or two of the herbicides evaluated (2,4-D, glyphosate, ammonium glufosinate). No biotype with resistance to diquat and saflufenacil was found.

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