Surveillance and mapping of tribenuron-methyl-resistant weeds in wheat fields

Tribenuron-methyl (TBM) is among the herbicides that are widely used for controlling broadleaf weeds in wheat fields in Iran due to its low mammalian toxicity and environmental risk, use at low doses, the broad spectrum of weed control, and low price compared to other herbicides. However, wheat farmers' repeated application and dissatisfaction with the optimal and effective control of the TBM herbicide have led to investigating broadleaf weed resistance in Iranian wheat fields. For this purpose, through a national call in 2018, a total of 240 broadleaf weed populations belonging to 13 species and 7 plant families were collected from 153 wheat fields in 72 counties across 14 provinces suspected to be resistant to the TBM herbicide. Then, a screening test was conducted in a completely randomized design with 5 replications of each biotype using the recommended dose of 25 g a.i. ha^{- 1} of TBM in the greenhouse. Overall, the results indicated that 124 (51.7%) of the screened populations were resisted to TBM. Specifically, 44 populations (81%) of Sinapis arvensis L., 18 populations (45%) of Malva neglecta Wallr., 25 populations (45%) of Silybum marianum (L.) Gaertn, 2 populations (66.6%) of Ammi majus L., 1 population (50%) of Rapistrum rugosum L., 3 populations (21%) of Descurainia Sophia (L.) Webb ex Prantl, 9 populations (36%) of Vaccaria hispanica Mill., 8 populations (48%) of Galium aparine L., 9 populations (75%) of Melilotus indicus L. According to the Adkins and Maas evaluation, 4 populations (100%) of Raphanus raphanistrum L. were classified as resistant to TBM. This study is the first comprehensive investigation of broadleaf weed resistance to TBM across Iranian wheat fields, providing crucial insights for future herbicide management strategies. Given the high incidence of resistance, continued use of TBM in Iranian wheat fields may lead to increased yield loss and environmental pollution. Additionally, it is necessary to investigate cross-resistance in resistant populations to other ALS-inhibiting herbicides.