Coulman, B., Loeppky, H. and Entz, M. 2015. The effect of late fall seeding time on the seed production of Italian ryegrass. Can. J. Plant Sci. 95: 641Á645. Italian ryegrass (Lolium multiflorum Lam.) is a cool-season grass, which behaves as an annual in the Great Plains region of western Canada and is used as a grazing crop. Italian ryegrass requires vernalization for reproductive development to occur. Late fall (dormant) seedings, which have been used for annual crop species, have often resulted in earlier developing seedlings in the spring and higher yield than spring seedings. For Italian ryegrass, dormant seedings may result in vernalization of early-spring-germinating seedlings, allowing seed production without having to overwinter established plants. The objective of this study was to compare the seed yield and stand establishment of late fall (dormant) and spring seedings of Italian ryegrass at three locations in the Great Plains region of western Canada. Stand establishment was assessed by measuring tiller density in the month of June, and these densities were greater for spring than late fall seedings. Most spring seedings had no reproductive development and, thus, no seed yield; however, most late fall seedings produced seed the following year, indicating that vernalization of early-developing seedlings did occur. There were significant differences in seed yield among the four cultivars tested and among sites. Based on the high variation in seed yield among cultivars and sites and the relatively low yield levels obtained, late fall seedings of Italian ryegrass cannot be recommended in the Great Plains region of western Canada.Key words: Seeding time, dormant seeding, seed production, vernalization Coulman, B., Loeppky, H. et Entz, M. 2015. Incidence d'un semis automnal tardif sur la production grainie`re de l'ivraie multiflore. Can. J. Plant Sci. 95: 641Á645. L'ivraie multiflore (Lolium multiflorum Lam.) est une gramine´e de saison froide se comportant comme une annuelle dans la re´gion des grandes plaines de l'Ouest canadien, et on y recourt pour la paissance. Pour se reproduire, l'espe`ce doit subir une vernalisation. Les semis effectue´s a`la fin de l'automne (en dormance), comme on le fait pour les cultures annuelles, donnent souvent des plantules plus pre´coces le printemps suivant, d'un rendement supe´rieur a`celui des plantes seme´es au printemps. Dans le cas de l'ivraie multiflore, les semences en dormance peuvent entraıˆner la vernalisation des plantules qui germent au de´but du printemps et amener les plants a`monter en graine sans que ceux-ci aient a`traverser l'hiver. L'e´tude devait comparer le rendement grainier et l'e´tablissement des peuplements d'ivraie multiflore apre`s des semis tardifs a`l'automne (dormance) ou des semis printaniers, a`trois emplacements, dans les grandes plaines de l'Ouest canadien. L'e´tablissement des peuplements a e´te´e´value´d'apre`s la densite´des talles en juin, et il e´tait plus important pour les plants seme´s au printemps que pour ceux seme´s a`la fin de ...