Argentina registers first case of Bassia scoparia resistant to ALS herbicides

The Pest Management Network of the Argentine Association of Direct Seed Producers (Aapresid) confirmed the first instance of resistance of the weed, Bassia scoparia, to ALS herbicides in Argentina, which was detected in the west of the province of Buenos Aires.

This case brings the list of resistant biotypes in Argentina to 44, with 14 being resistance to this mode of action.

The resistance of the weed was verified by a combined team of researchers from the National Institute of Agricultural Technology (INTA), the National Scientific and Technical Research Council (CONICET), and the Faculty of Agronomy.

Globally, 55 cases of resistance of this annual spring-summer weed, which is widely distributed in sandy and saline soils, to various groups of herbicides (ALS, Auxins, Glyphosate, and PSII) had already been reported in Canada and the USA, with 11 instances having multiple resistance to two, three and even four sites of action.

Aapresid stressed that no resistance had been reported in Argentina, but during previous campaigns, consultations were made regarding difficulties for its control in the east of the province of La Pampa and the west of Buenos Aires, a sunflower cultivation region.

A survey by Aapresid’s partners estimate that some 87% of sunflowers planted nationwide were imidazolinone-tolerant hybrids, of which 93% were concentrated in these regions, correlating with an increase in the use of assets from this weed control family.

″As currently known, the exclusive dependence on herbicides as a control method, as well as the repetitive use of the same mode of action, increasingly favor the selection of resistant biotypes,″ Aapresid warned.

The research team confirmed this resistance for two active agents from the imidazolinone family, which apply to the site of action of acetolactate synthase (ALS) inhibitors.

The work measured the level of sensitivity to imidazolinones of three allegedly resistant populations through dose-response experiments, taking the seeds of suspicious plants from the areas in question, which were compared with a susceptible population from a cattle lot in an area with no history of herbicide use.

A mixture of imazapyr (Clearsol WG 80%) + imazamox (Trigosol WG 70%) was then applied at increasing doses when the plants had approximately 10 leaves and were 6 cm in height.

Thirty days after the application, the survival percentage was determined, verifying that surviving plants from resistant populations completed their cycle and produced viable offspring.

The evidence also enabled researchers to confirm the resistance to imidazolinones (ALS) of the Bassia scoparia populations collected. Current studies are being conducted to determine the resistance mechanisms involved.

(Editing by Leonardo Gottems, reporter for AgroPages)