EFFECT OF DIFFERENT CONTROL METHODS OF IMPER ATA CYLINDRICA ON COCONUT (COCOS NUCIFERA) YIELD IN LOW COUNTRY DRY ZONE OF SRI LANKA

Five methods of control of Imperata cylindrica (L.) Beauv namely a) harrowing with disc harrow, b) Glyphosate (N- Phosphonomethyl Glycine) 2.88 kg a.i / ha, c) Glyphosate 1.44 kg a.i/ha, d) circle weeding with Glyphosate (1.44 kg a.i/ha) along with mechanical slashing rest of the area, and e) mechanical slashing were evaluated to determine the cost effective method of control of Imperata cylindhca, and to ascertain the effect of coconut -Imperata competition on yield of coconut in Low Country Dry zone in Sri Lanka. An unweeded plot was used as the control. Experiment was arranged in a Randomized Complete Block design with three replicates. Treatments were applied twice a year in six months interval. Glyphosate at the rate of 2.88 and Glyphosate 1.44 kg a.i/ha gave a significant reduction (P increase (P in plots with these treatments at two years after imposition of treatments .When cumulative average yield of coconut was considered for three consecutive years, control of Imperata with Glyphosate gave a 54% increase (P'O.01) of nut yield when compared to the unweeded control. Cost - benefit analysis of different control methods revealed that the application of Glyphosate at the rate of 1.44 kg a.i/ha was the most cost effective (undiscounted B/C ratio: 5.9) method of control of Imperata in sandy soils in the Low Country Dry Zone of the Coconut Triangle.