Effects of density and date of emergence of redroot pigweed (Amaranthus retroflexus L.) on sugar beet (Beta vulgaris L.) yield

Effects of density and emergence date of redroot pigweed (RP) (Amaranthus retroflexus L.) on sugar beet (Beta vulgaris L.) yield were studied as a factorial experiment based on randomized complete block design with three replications was carried out. Treatments were five weed densities (1, 4, 8, 12 and 16 weeds per meter of row) at four relative times of weed emergence (simultaneous with and 10, 20 and 30 days after sugar beet emergence (DSE)) and a weed-free control. The results showed that early emergence along with high weed densities, phyllochrony of the sixth and seventh leaves were increased from 4 days in the control to 9 days in some treatments. Red root pigweed green cover ranged from zero in 1 RP per meter in row at 30 days after sugar beet emergence to 59% in full season interference (FSI) of 16 RP per meter in row. Leaf area index in sugar beet was reduced due to high weed density and early RP emergence, and the weed density was more effective than time of emergence. FSI of 16 RP per meter of row decreased sugar beet root yield to 23% as compared with the control. Economic damage of RP on sugar beet was started, when four RP per meter grew with sugar beet at least 20 DSE until late growing season. Sugar yield varied from 12.88 t. ha-1 in one RP per meter 30 DSE to 8.58 t. ha-1 in FSI of 16 RP per meter.