A field experiment entitled “Weed diversity and its interference in pea (Pisum sativum L.)” was conducted in rabi season of 2020-21 at the experimental farm of College of Post Graduate Studies in Agricultural Sciences (CAU, Imphal), Umiam. The experiment consisted of 14 treatments, which were divided into two sets, viz., weedy and weed free. The weedy set of treatments consisted of weed free following 10, 20, 30, 40, 50 and 60 DAS and weed free control, whereas the weed free set consisted of weed free plot until 10, 20, 30, 40, 50 and 60 DAS and never weed free. The treatments were replicated thrice and arranged in a randomised block design with test crop of pea. Experimental results showed that the longer duration of weed free period synergistically influenced the growth parameters (plant height, number of branches, leaf area, LAI and dry matter accumulation), Physiological parameters (days to 50% flowering and CGR) and yield attributes (number of pods plant-1, number of seed pod-1, pod weight plant-1 and seed index), pod yield, stover yield, harvest index, nutrient content and uptake by plants, while the longer duration of pea-weed interference led to significant reduction in the values of all above parameters. However, weed dynamics revealed the presence of 13 different species of weeds during the cropping season. Galinsoga parviflora was identified as the most dominant species according to the important value index, followed by Oxalis acetocella, Echinochloa crusgalli, Bidens bipinnata and Polygonum aviculare. The weed density increased upto 60 DAS and decreased thereafter. While, the weed dry matter accumulation and weed growth rate tend to increase progressively with duration of weedy period. Linear, quadratic and cubic regressions showed negative relations between Pea yield with weed density and its dry weight. The relative yield of weedy and weed free set of treatments followed logistic and Gompertz equation, respectively. These equations were used to determine 21 to 48 DAS as the critical period of pea-weed competition at 5% RYL, which is equivalent to 260 to 510 GDD. The Economic Threshold Level for multi weed species for pea was 2.15 to 20.91 plants m-2. The practical implication drawn from the study is that, for providing competitive advantage to pea against the weeds, the weeding should begin at 21 DAS and during the entire critical period which ranged upto 48 DAS the weed population in the field should not exceed 20.91 plants m-2.