Effect of planting date on weed competition in pesticide-free flax.

摘要

A field experiment was conducted in central and northernwestern Iowa, USA, during 2006 to study the effect of sowing date (11 April, 21 April and 5 May) on weed competition in pesticide-free flax cultivars Bethune, Carter, Hanley, Norlin and York. The 4 predominant weed species were giant foxtail (Setaria faberi), lambsquarter (Chenopodium album), waterhemp (Amaranthus rudis [Amaranthus tuberculatus]) and Pennsylvania smartrweed (Polygonum pennsylvanicum). At central Iowa, flax yield decreased significantly with sowing on 5 May (81 kg/ha) than 11 April (1199 kg/ha) and 21 April (697 kg/ha). Common cocklebur (Xanthium strumarium), barnyard grass (Echinochloa crus-galli) and fall panicum (Panicum dichotomiflorum) were also present. The total weed biomass was statistically similar for all sowing date. Waterhemp and smartweed populations generally increased with later sowing date while giant foxtail decreased and lambsquarter remained stable. At northwestern Iowa, flax yield in 11 April sowing (1698 kg/ha) was slightly higher than those in 21 April (1370 kg/ha) and 5 May (1424 kg/ha). Weed biomass was dominated by lambsquarter and waterhemp, but small populations of smartweed and barnyard grass were also measured. The total weed biomass was influence by the amount of lambsquarter present, particularly in 21 April sowing. Waterhemp populations increased with later planting. In 11 April and 5 May sowing, the total weed biomass was statistically similar and significantly lower than that in 21 April sowing.