Horseweed found to have glyphosate resistance along Spanish railways
The genus Conyza, also known as horseweed, butterweed, or fleabane, are broadleaf weeds that occur in many crops but are also common in non-crop systems such as roadsides, railways, and public gardens. Conyza species have selected for glyphosate resistance along railway tracks from Southern Spain, due to the misuse of this herbicide and the high seed dispersal rate of these species.
In a new study, 23 samples of the genus Conyza (11 from C. canadensis and 12 from C. bonariensis) were collected from the margins of railways in different routes of the Andalusian railway network running adjacent to nearby crop fields.
Read this paper in the Canadian Journal of Plant Science
The glyphosate resistance level of the Conyza populations was evaluated through a metric called GR50 (rate causing 50% growth reduction) and resistance factor (RF) in every population collected. Results showed that, among all the C. canadensis populations collected, 18.2% were glyphosate-resistant (RF greater than 10), 45.5% showed a tendency to develop resistance (RF between 2.5 and 5), and 36.4% were susceptible (resistance factor < 2.5).
Of the 25% of C. bonariensis populations that had resistance to glyphosate, 16.7% had a moderate resistance (RF between 5 and 10) and 58.3% were susceptible. This study found that there are already glyphosate-resistant Conyza species along the railway networks in southern Spain. This could lead to a possible seed exchange between railways and adjacent places (both neighboring crop and non-crop areas). As a result, it is very important to consider the railway network when planning control measures to avoid resistance level increases along railway networks and their neighboring areas.
Read the full paper — Selection for glyphosate resistance in Conyza spp. occurring in the railway network of southern Spain by Ignacio Amaro-Blanco, María D. Osuna, Yolanda Romano, Rafael Roldán-Gómez, Candelario Palma-Bautista, João Portugal, and Rafael De Prado
