Management and emergence dynamics of herbicide-resistant Lolium multiflorum Lam in winter cereals of Argentina.

VIGNA, MARIO; LOPEZ, RICARDO; GIGÓN, RAMÓN; SABBATINI, MARIO RICARDO; LODOVICHI, MARIELA; CHANTRE, GUILLERMO RUBÉN

Miami Beach, Florida, USA

Conferencia; Pan-American Weed Resistance Conference; 2010

Bayer CropScience

          Lolium multiflorum (Graminaceae, LOLMU) is a widespread annual weed allogamous in Argentina, affecting crops of wheat (Triticum aestivum) and barley (Hordeum vulgare) in the humid Pampas, northern Patagonia and Mesopotamia.  Surveys carried out in the S and SW of the province of Buenos Aires in 2006 and 2007 indicate that LOLMU is the second most frequent weed in wheat crops after Avena fatua. In the EEA INTA Bordenave, the different lines of research on this topic began in 2003 after consultations undertaken by farmers about the difficulty of controlling LOLMU in the fallow period with the commonly recommended dose of glyphosate.          Performed studies showed the existence of LOLMU populations capable to survive glyphosate rates several times greater than that normally used for its control in the S and SW of the province of Buenos Aires. However, their presence would be still restricted to small areas coexisting with susceptible populations. To achieve satisfactory weed control, the presence of these populations in the wheat-fallow stage demand the use of graminicide herbicides, alone or in mixture with glyphosate. Subsequent studies in the region showed that applications of paraquat at juvenile stages may be a satisfactory alternative to control populations of LOLMU that survive rates several times greater than the normal dose of glyphosate. Demographic models allow the representation of a conceptual framework of a highly complex system, as the weed population dynamics, and its interaction with antropic (weed control practices), stochastic (climate) and economic (economic indicators of the agricultural activity) factors, showing a high practical applicability.     In order to be able to construct, validate and apply these models it is necessary to acquire knowledge about the bioecology of the crop-weed system, as well as, in relation the effect of the different management practices on the regulatory processes of the weed population dynamics. For this purpose, the determination of the ambient requirements for seed dormancy release of LOLUM and the associated germination requirements represents valuable information for the prediction of field emergence. Recent studies showed higher germination percentages from LOLMU seeds buried under field conditions compared to seeds stored at constant temperatures. From these it was inferred that seed exposure to fluctuating temperatures in the field would produce a significant increment in the dormancy release rate compared to a constant temperature regime.               Seeding emergence dynamics will be affected by chemical control practices, which efficacy will depend, among other factors, on the appearance of herbicide resistant biotypes. Under field conditions, in the area affected with herbicide biotype resistance, it was observed that the presence of LOLMU individuals in wheat crops would not be explained only by the survival to chemical control in the fallow but also by late emergence. Therefore, it is necessary to study seedling emergence of LOLMU biotypes which show a differential herbicide response.