Abstract: Field studies were conducted in 2006 and 2007 growing seasons to examine the competitive effects of common lambsquarters on sugar beet. The experiments were established as a randomized complete block design in a factorial arrangement of four common lambsquarters emergence times (0, 15, 30 and 45 days after sugar beet) and four common lambsquarters densities (0, 5, 10 and 15 plants mG1 per row). Sugar beet LAI, biomass and white sugar yield were reduced with increasing common lambsquarters density and decreasing relative time of common lambsquarters emergence. The lack of an affect of late emerging common lambsquarters (45 days after sugar beet emergence) on sugar beet LAI and yield might be due to the common lambsquarters plants being smaller and their not growing above sugar beets until harvest. Seed production of common lambsquarters per m2 was increased with increasing density and decreasing relative time of emergence of common lambsquarters. Common lambsquarters produced greater biomass when it emerged with or 15 days after sugar beet than at later emergence times at all densities. This indicates the importance of time of emergence of common lambsquarters relative to sugar beet in affecting competition between them. These results suggest that sugar beet producer should implement common lambsquarters management strategies earlier than 45 days after sugar beet emergence in order to reduce negative effects of common lambsquarters on sugar beet yield.
