Response of purple nutsedge (Cyperus rotundus L.) to crop extracts prepared in various solvents

Plant allelochemicals have different solubilities in organic solvents. Laboratory studies were conducted to know the better solvent for extraction of sorghum (Sorghum bicolor L. Moench), Brassica (Brassica napus) and sunflower (Helianthus annuus) allelochemicals. Extraction efficiency of five solvents (water, methanol, ethanol, xylene and n-hexane) was compared with distilled water (control) and determined their effects on purple nutsedge growth. Extracts from three crops studied were used to irrigate as herbicides in pots under room conditions. Extracts of sorghum, Brassica and sunflower inhibited the shoot length and fresh and dry weight of purple nutsedge. The inhibition order of solvents was: water (highest inhibition) ≥ methanol ≥ ethanol >xylene > n-hexane and the order of inhibition of crop extracts was sorghum > Brassica > sunflower. Extracts with 50% concentration cause more suppressive effects than 5% concentration, because higher concentrations are supposed to have more amounts of phytotoxins in the extract. These findings showed that water is best solvent to extract naturally occurring allelochemicals in crop plants.