The occurrence of resistance to ALS and ACCase-inhibiting herbicides ryegrass (Lolium rigidum Gaudin) in Bizerte region

Ryegrass (Lolium rigidum Gaudin) is a most prevalent weed in Bizerte region and caused losses in yield. Farmers used herbicides to control ryegrass in cereal crops. Thirteen herbicides (ALS inhibitors, ACCase inhibitors and PSII inhibitors) were used in the field experiment to evaluate their efficacy and their effect on yields of wheat and of ryegrass. The trial was installed in Randomized Complete Block Design (RCBD) in Bizerte. Seeds of ryegrass collected from Bizerte during surveys were the subject of the resistance detection to the ALS inhibitor herbicides [AmilcarWG® (mesosulfuron+iodosulfuron)] and to the ACCase inhibitor herbicides [Topik® (clodinafop-propagyl)] by a pot experiment method. The results of the field experiment showed that only Tolurex® [Chlortoluron (PSII inhibitor)] has the best efficacy (83.6%), but all other herbicides (ALS and ACCase inhibitors) have insufficient efficacy on ryegrass. Then, over 60% of ryegrass populations were escaped to treatments ACCase and ALS-inhibiting herbicides that are not statistically different. The low efficacy of herbicides (ALS and ACCase inhibitors) was not explained by a high density of ryegrass, but by the presence of herbicide resistance in ryegrass populations in Bizerte. These results were confirmed by the pot experiment method. The count of the surviving plants of ryegrass (30 DAT) in pot experiment method revealed that 70% of ryegrass populations are resistant to both herbicides inhibitors (ACCase and ALS). Similarly, the percentage of reduction in fresh weight of ryegrass, compared to untreated control, showed over 80% of the ryegrass populations was resistant to ACCase inhibitor herbicides and to ALS inhibitor herbicides.