Threshold level, Trianthema portulacastrum, Onion

A field investigation was carried out during rabi 2007 at Tamil Nadu agricultural University, Coimbatore to evaluate the threshold values of horse purslane (Trianthema portulacastrum) in onion. Increase in densities of T. portulacastrum increased the yield reduction linearly in onion crop. The maximum percentage of yield reduction was recorded with 64 weeds/m2 (54.8%) over the zero weeds/m2. The lowest yield reduction was with 4 weeds/m2 (8.8%) followed by 8, 16, 32 weeds/m2 ( 27.1, 38.61, 46.38% respectively). It is evident that a density of 4 weeds/m2 was the threshold value of Trianthema portulacastrum for onion crop to avoid significant yield reduction.