Are wheat hybrids more affected by weeds than conventional varieties?

Wheat hybrids have been cultivated in Europe on 250.000 ha in 2013. Hybrids are commonly seeded at much lower seeding rate compared to the common varieties; the low seeding rates may results in lower competitive ability of hybrids toward weeds, especially during first growth stages of the crops. A field-experiment was conducted to compare weed density and yields performance of conventional varieties and hybrids. The study was carried out during the campaign 2013-2014 in Piemonte, north west of Italy, at three sites (Borgo d’Ale, Moncrivello and Grugliasco) characterized by different soils and weed infestation conditions. The varieties compared were the conventional Illico, and the hybrids Hystar and Hyxo, seeded at 220 kg/ha, 75 kg/ha and 60 kg/ha, respectively. Four plots (7m2 each), covered by plastic films during herbicide spraying, were randomly selected in contiguous fields cultivated with the three varieties indicated above. In each plot weed density (plants/m2) and weed cover on the ground (\%) were evaluated. Weed assessments, three reps per plot, were performed two times during the growing season (at early tillering stage and at the beginning of stem elongation). Overall, the highest weed densities were generally encountered in the fields cultivated with hybrid varieties, with Hystar in particular. At Borgo d’Ale the most abundant weeds were Stellaria media, Matricaria chamomilla, Panicum dichotomiflorum and Viola tricolor; at Moncrivello Stellaria media and Veronica persica; at Grugliasco Poa spp., Stellaria media, Veronica persica and Ranunculus arvensis. Overall, at the first assessment, no significant differences were found between varieties. Differences between the conventional varieties and hybrids were larger at the second assessment, when climatic conditions were more favorable to weed growth. Weed infestation was rather diversified at the three sites. At Borgo d’Ale at the second assessment, the weed density was 198 plants/m2, 192 plants/m2 and 128 plants/m2, in Hystar, Hyxo and Illico cultivars, respectively. At Moncrivello, during the same assessment, the highest weed density was 242 plants/m2 in Hystar plots, while nonsignificant differences were noted among Hyxo (172 plants/m2) plants/m2 and Illico (161 plants/m2). At Grugliasco the weed infestation was lower compared to the other sites: 56 plants/m2 in Hystar and Hyxo plots, and 60.8 plants/m2 in Illico, without significant differences. Similar results were obtained in terms of weed cover with the highest values (between 40\% and 60\% at the second assessment), observed in hybrid plots. The yields were not significantly affected by the varieties, regardless the site location. In conclusion, the degree of weed infestation in hybrids was in general higher than in conventional varieties. However, the high tillering ability of hybrids allows them to contain efficiently weed competition, without significant impact on yields.