Minimum weed-free period for sugarbeet (Beta vulgaris L.) in the Gharb region of Morocco

The objective of this research was to determine the minimum period during which fall-seeded sugarbeet should b e kept weed-free in the Gharb region of Morocco to limit root and extractable sucrose yield loss, and to determine the persistence of weed control with preemergence (PRE) or postemergence (POST) herbicides. Continuous post-planting hand-weeding for 17 weeks and 15 weeks in 1990, and for 15 weeks and 12.5 weeks in 1991 were required to limit sugarbeet root yield loss to 5% and 10%, respectively. Sucrose content did not vary with increasing weed-free duration. Weed dry weight produced during the growing season and the reduction of cumulative leaf area duration explained most of the reduction in sugarbeet root yields. High cumulative leafarea duration was the result of high leaf area expansion rate. PRE herbicides gave poor weed control and resulted in 100% and 85% sugarbeet yield loss in 1990 and 1991, respectively. The combination of P RE and POST herbicides improved weed control, but yield loss was still significant ; 34% in 1990 and 48% in 1991. Nomenclature: Pyrazon, 5-amino-4-chloro-2­ phenyl-3(2H )-pyridazinone; Ethofumesate, «±)-2­ eth oxy-2,3-dih ydro-3,3-dimethyl-5-benzofuranyl methanesulfonate); Fluazifop, (R)-2-[ 4-[[5-( trifluoro­ meth y 1)-2-pyrid inyl]oxy]ph enoxy] propanoic acid; Lena cil, (3-cyclohexyl-6,7-dihydro-l H-cyclopenta­ pyrimidine-2,4(3H, 5H )-dione; Phenmedipham, 3­