Critical Period of Weed Control in Sugar Beet in Shahrekord region

Weed competition is one of the yield-limiting factors of sugar beet production in Iran. Weed competition may reduce the root and sugar yield, depending on the weed density and the intensity of weed competition with the crop. In order to determine the critical period of weed control (CPWC) in sugar beet in Shahrekord region, an experiment was arranged in a randomized complete block design with 14 treatments and four replications in 1999 and 2000. Treatments included weed-free plots until 2, 4, 6, 8, 10 and 12 weeks after planting (WAP) in 2000 (in 1999 based on the stages of crop growth in the form of weed control, treatments were until 4, 6, 8, 10, 12 and 14 – leaf stages of sugar beet) and weed-infested plots from 2, 4, 6, 8, 10 and 12 weeks after planting sugar beet in 2000 (in 1999 based on the stages of crop growth in the form of weed interference until 4, 6, 8, 10, 12 and 14 - leaf stages of sugar beet). Two control treatments (full-season control of weeds and full-season interference of weeds) were also included. The results showed that weed infestation significantly (Pthe root and sugar yield of sugar beet in all treatments. Total root yield loss of the crop Correspondence to: F. Salehi, E-mail: foroud_salehi@yahoo.com 2 F.Salehi et al in full competition was 92.9 % in 1999 and 61.16 % in 2000 compared to weed free control treatment. Based on 10% loss of yield, the beginning of the critical period of weed control (CPWC) was 25 and 5 days after planting for the first year and the second year, respectively. On this basis, the end of the critical period of weed control was 78 days for the first year and 88 after planting for the second year. Dominant weeds in this experiment were Amaranthus retroflexus, Chenopodium album, and Echinochloa crus-galli. Considering the high density of weeds in the experimental site, a long critical period of 82 days existed five days after planting. Also, with regard to late planting date of sugar beet (from May to June), competition between weed and crop may start sooner, causing considerable yield loss in sugar beet.