Floristic divergence of weeds in rice fields under subtropical condition

Weed infestation pattern changes over time for continuous adaptation of similar weed control methods. So, a survey was conducted at Agronomy Field Laboratory, Bangladesh Agricultural University from July 2019 to June 2020 to identify the most dominant and abundant weed species as well as to indicate the probable problematic weed in boro and T. aman rice. Seven fields were randomly selected for each of the boro and T. aman rice. The surveys were performed according to quantitative survey technique by using 0.25m2 quadrate with 16 samples from each of the field following the zig-zag method. Sampling was done twice, while the rice plants were at the vegetative stage and at reproductive stage. Fifty one weed species under 23 families were recorded at experimental area of which 42 species (under 18 families) and 38 species (under 20 families) were observed in boro and T. aman, respectively. Poaceae topped the list with 10 species, while Cyperaceae ranked second with six species. The highest number of weed species (no. 42) was observed in boro rice compared to T. aman rice (no. 38). Besides, divergence in the weed composition was also high between both rice fields. Among the 11 abundant weed species, Eleocharis atropurpurea, Echinochloa crusgalli and Monochoria vaginalis were the most frequent and abundant weed species found in both boro rice and T. aman rice. Broadleaves had higher abundance value (246.26% in boro and 332.39% in T. aman) than grasses (188.76% in boro and 146.68% in T. aman) and sedges (164.98% in boro and 120.93% in T. aman). Moreover, the annuals were dominant over the perennials. Therefore, the present results having diversified weed species with different ranks and orders indicated that the weed management strategies should be taken regarding the infestation of dominant weed species of the respective crop.