By Leonardo Gottems, Reporter for AgroPages
Every two years since 2013, the Pest Management Network (REM) has conducted surveys on major resistant and tolerant weeds in Argentina, and this year will be no exception.
Some 27 weeds were found to be of concern, with 21 being resistant and six tolerant, in 200 areas and regions covering 29 million hectares of agricultural land.
The survey drafted maps that will prove to be useful for various parties throughout the country’s production chain, while enabling producers and consultants to discover if weeds are present in their areas of influence before they are seen. Therefore, they can start paying more attention.
Currently, all relevant parties are aware of the survey, which identified, in real terms, resistant and tolerant weeds in 401 parties and departments that were not identified in 2017.
From a macro pint of view, the national situation can now be analyzed. Regarding the weeds that are most widely geographically dispersed, Conyza sp is the most common, with a presence in 99% of the regions and areas surveyed, followed by the Amaranthus quitensis at 90%, then the grasses, Digitaria sanguinalis, Sorghum halepense, Chlorideas and Echinochloa, which are present in around 70% to 80% of these areas.
These are followed by Lolium at 60%, then by Borreria verticillata, Pappophorum and Perennial Gonfrena at 40% to 50%. Of the ten weeds mentioned that are resistant or tolerant to glyphosate
, 60% are grasses and the remaining 40% are broadleaf species.
But the situation changes if the weeds analyzed are those that grew the most in the last two years when evaluating the number of new areas and regions where they were reported. Firstly, glyphosate-resistance turnips have appeared, including the species, Brassica rapa and Hirschfeldia incana, followed by Amaranthus quitensis and the Digitaria sanguinalis, which are resistant to glyphosate but to 2.4D. Sorghum halepense is also resistance to graminicides Acetil CoA Carboxilasa (ACCasa).
Subsequently, Gonfrena pulchella, which is glyphosate tolerant, has also been identified, as well as acetolactate synthase (ALS) resistant Echinochloa and Pappophorum, along with glyphosate-resistant Echinochloa and Chloridea. The proportion of grasses and broadleaves has stayed at 60% and 40%, respectively.
Another key issue is that in this second list, along with the appearance of glyphosate-resistant and tolerant weeds, other factors are also present, such as ALS, ACCase and Hormonal graminicides. Although the weeds with greater geographic dispersion are those resistant and tolerant to glyphosate, biotypes resistant to other herbicides are also spreading, in many cases with multiple resistance to glyphosate.
This clearly complicates the situation, makes management more expensive, and highlights the importance of an overall approach. It is not just enough to change the herbicides used. Monitoring, rotations, service cultures and selective applications are no longer options, they are now necessities.