WEED DIVERSITY IN THE TRANS-HIMALAYAN WHEAT FIELDS OF UPPER MANANG, NEPAL

The study was carried out in Nyeshang valley of upper Manang, which is situated in the TransHimalayan, rain-shadow region in central Nepal. Weeds were sampled/collected in and around the crop fields during the months of May and September of 2005 within an altitudinal range of 3200 m at Pisang to 3900 m at Khangsar. A total of 71 species of weeds were accounted during field sampling. They consisted 59 species of dicots, 11 species of monocots and 1 species of pteridophyte. Forty three weeds were found to occur within wheat fields. Study showed that the list included 4 species of alien weeds to Nepal. Frequency and density of dominant weed species were also substantiated. The dominant weed species included Chenopodium album, Phleum alpinum and Convolvulus arvensis. Hypecoum leptocarpum, Melissa axillaris, Cynoglossum zeylanicum and Arisaema jacquemontii showed sporadic occurrence. Higher weed diversity was found at the elevation of 3470 m at Braka. Phleum alpinum was the most dominant weed with average density of 28 individuals per m² while Convolvulus arvensis was found to be most problematic weed creating problem during harvest. Avena fatua, Pennisetum flaccidum and Phleum alpinum were taken as mimicry weed species since they showed similarity in appearance with wheat in their vegetative morphology.