Economical yield loss threshold of weed control in polygerm and monogerm sugar beet cultivars

Producing high yielding sugar beets is the goal of all sugar beet growers. In order to determine the economical yield loss threshold of weed control in sugar beet an experiment was conducted during 2008-2009 at the Agricultural Research Station of Islamic Azad University of Tabriz, Iran. The sugar beet hybrids IC (a polygerm) and 273 (a monogerm) were sown with a density of 83,000 plants ha -1 . Weeds grew along the crop until 4, 6, 8 and 10 days after sugar beet emergence and late growth season and also a weed-free treatment was used. Results revealed that there was a reverse trend between weed and crop biomasses. Weed biomass increased from nearly 47 g m -2 in competition until 4-leaf stage to 74 g m -2 , when interference duration extended up to 10-leaf stage of sugar beet. The greater yield was produced by weed-free plots and the lowest by full-season interference treatment. When weeds competition extended until 10-leaf stage, sugar concentration was reduced significantly from 17.9 to 12.1%. Economical yield loss threshold of studied weeds was at 10-leaf stage of sugar beet in both varieties. The stepwise regression analysis verified that the weed and crop biomasses and root yield had a marked increasing effect on sugar yield of sugar beet.