Weed species and their damage in rice fields in Zhejiang

Surveys were made for weed species and their damages in rice fields in Jiaxing, Hangzhou, Jinhua, and Wenzhou, Zhejiang Province in 1986-2000 by a collaborative team of scientists. It involved early rice, late rice, one season rice, rice nursery or direct seeding rice, transplanted rice by seedling broadcasting, arid rice nursery. The result showed that there are 131 species and 2 varieties belonging to 77 genus and 41 families of weeds appearing in rice fields in Zhejiang, among which 41 species and 1 variety belonging to 35 genus and 21 families are dominant. They are Echinochloa crusgalli, Leptochloa chinensis, Paspalum distichum, Cyperus difformis, Alternanthera philoxeroides, Monochoria vaginalis, Sagittaria sagittifolia, Rotala indica, Eleocharis yokoscensis, Ludwigia prostrata, et al. Weeds have the heaviest damage to one season rice, heavier to late rice, and the least to early rice. In simple weed community in early rice fields, E. crusgalli is only one main weed, whereas weed community in late rice fields is complex and consists of E. crusgalli, broad leaf weeds and sedge weeds. The damage of weeds is heavier in fields of direct seeding rice and transplanted rice by seedling broadcasting than in conventional cultivation fields, and there are more weed species in arid rice nursery than in paddy rice nursery. Since long application of herbicides, annual weeds have decreased, perennial weeds increased, while E. crusgalli keeps its main place in rice fields. A list of weed species in rice fields was appended at the end.