Three field experiments were conducted during 94/1995, 95/1996 and
97/1998 seasons to study the effect of some herbicide treatments on growth
characteristics, yield and chemical constituents on onion (Allium cepa L.) plant. Plant
height and number of leaves/plant were significanlly decreased when a single
application of oxyfluorfen or methabenzthiazuron or fluazifop-butyl was applied at 21
days after sowing (OAS.). The highest significant dry weighUplant and total bulb
yield were obtained when onion plants were treated either oxyfluorfen or
methabenzthiazuron plus fluazifop-butyl were applied twice at 21and 63 D.A.S.
Chlorophytls (a and total) concentrations showed the lowest values when a single
application of fluazltop-butyl (125 or 250 g a.iJfeddan=fed.) was applied at 21 or 42
DAS. All herbicides combination treatments increased total nitrogen concentration in
onion leaves, while phosphorus and potassium concentration were not affected.
Single application of fluazifop-butyl at 125 or 250 9 a.i.lfed. Significantly decreased
hydrolysable carbohydrates concentration in onion leaves. Oxyfluorfen alone or in
combination wilh nuazifop-butyl increased the hydrolysable carbohydrates
concenlration in onion leaves. All weed treatments did not alter the studied chemical
constituents of the harvested onion bulbs. Thus, the best chemical weed control
treatment in direct-seed onion is to apply oxyfluorfen (90 + 180 g a.i.lfed.) or
methabenzthiazuron (350 + 700 9 a.i./fed.) with fluazifop-butyl (125 + 250 9 a.i./fed.)
in two applications at21 and 63 D.A.S.