Occurrence and distribution of triazine-resistant Chenopodium album in Slovenia

In recent years the number of sites in Slovenia with insufficient herbicide control of weeds in maize has increased. Therefore, since 1994, a project at the Institute of Hop Research and Brewing Zalec, Department of Plant Protection, is in progress in order to detect herbicide resistant weed biotypes in Slovenia and to develop weed control strategies. This contribution deals only with Chenopodium album, one of the most common and frequent weed species in maize fields in Slovenia. For testing of resistant and sensitive biotypes different methods were used: field treatments, biological tests under controlled conditions and flotation of leaf discs. In addition, the resistance ratio of the C. album seed bank was calculated. Samples collected in 1994 and 1995 from 100 fields where maize is grown strongly indicate that resistant biotypes of C. album are to be found in all parts of Slovenia, especially in locations where maize is grown in monoculture. Samples from fields with a 2-year crop rotation included only two cases with resistant plants while no resistant plants were found in the fields with a 3-year crop rotation. As we estimate that less than 10 % of maize is grown in monoculture, the incidence of resistant C. album indicates that less than 3 % of the fields in Slovenia where maize is grown are infested with resistant biotypes of C. album.