plants Communication Growth Stage of Alopecurus myosuroides Huds. Determines the Efficacy of Pinoxaden Ana Pintar 1,*, Zlatko Sveˇcnjak 2 , Valentina Šoštarˇci´c 1, Josip Laki´c 1, Klara Bari´c 1, Dragojka Brzoja 1 and Maja Š´cepanovi´c 1 1 Department of Weed Science, University of Zagreb Faculty of Agriculture, Svetošimunska Cesta 25, 10 000 Zagreb, Croatia;
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[email protected] (J.L.);
[email protected] (K.B.);
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[email protected] (M.Š.) 2 Department of Field Crops, Forages and Grasslands, University of Zagreb Faculty of Agriculture, Svetošimunska Cesta 25, 10 000 Zagreb, Croatia;
[email protected] * Correspondence:
[email protected]; Tel.: +385-1-2393-606 Abstract: Alopecurus myosuroides Huds. is an important pinoxaden-resistant grass weed in many countries of Europe. Recently, the low efficacy of pinoxaden was reported in winter cereals in Croatia, but a preliminary dose–response trial showed no herbicide resistance for the investigated weed pop- ulation. Therefore, a two-year experiment was conducted under greenhouse conditions to determine the efficacy of various pinoxaden doses (20, 40 and 80 g a.i. ha−1) on weed visual injuries and biomass reduction after herbicide application at different growth stages. As expected, the maximum weed biomass reduction (97.3%) was achieved by applying the highest dose (80 g a.i. ha−1) at the earliest −1 growth stage (ZCK 12–14). A pinoxaden dose of 20 g a.i. ha resulted in satisfactory weed biomass reduction (88.9%) only when applied at ZCK 12–14. The recommended dose (40 g a.i.