Ryegrass (Lolium rigidum Gaud.) developed resistance to Acetolactate Synthase (ALS) and Acetyl-CoA Carboxylase (ACCase) inhibiting herbicides. The objective is to evaluate the effect of the active substance ‘Prosulfocarb’, sprayed in post-sowing preemergence at different rates and associated with S-metolachlor on ryegrass resistant to registered rate (3200 g ha-1) and according to the stages of application (SAP1: 1 day after sowing of wheat, SAP2: 7 days after sowing and SAP3: 2 to 3 leaves after emergence). The study also evaluated the effect of Prosulfocarb and post-emergence herbicides on durum wheat yield and its components. To meet these objectives, field trials were carried out in northern Tunisia (Mateur/Bizerte), with a Randomized Complete Bloc Design (RCBD). The evaluation was carried out over three successive seasons (2012/13 to 2014/15). The results revealed that the efficacy of prosulfocarb improved with increasing application rate. The S-metolachlor favored the improvement of prosulfocarb efficacy by 6 to 15%. Results also showed that the efficacy of prosulfocarb was better in the first two growth stages of the application (SAP1 and SAP2) and low when applied after emergence (SAP3). Prosulfocarb allowed a gain of 7.3% of durum wheat yield. The ryegrass infestation (92.5 plants/m²) affected the number of grains per spike and caused durum wheat yield losses of up to 39%.

Key words: Herbicide, yield loss, Prosulfocarb, Ryegrass, Resistance, Tunisia.