Xu GaoFeng

Harmful effects and chemical control study of Mikania micrantha H.B.K in Yunnan, Southwest China

Invasive alien species Mikania micrantha, which originated from Central and South America, has spread quickly and become one of the most seriously invasive weedy species in Yunnan Province, Southwest of China. The harmful effects of this plant on major cash crops and local plant communities have been surveyed in 50 townships of 6 counties of Yunnan Province since 2006. Moreover, bioactivity and selectivity of 20 types of herbicides on M. micrantha and farming crops have been tested and analyzed since 2007. The results showed that M. micrantha is mostly distributed in subtropical and tropical areas of Yunnan, such as Lincang District, Baoshan District and Dehong Prefecture. The species has resulted in a series of negative impacts on farming cash crops and local plant communities. Compared with the control effects of 20 soil and foliar-applied herbicides, soil-applied herbicides Atrazine, Bensulfuron methyl and Prometryne have higher bioactivity and selectivity to M. micrantha germination and seedling. Foliar-applied herbicides Sulfometuron methyl, Starane and Glyphosate have better control efficiency on M. micrantha growth, but the security is low. As a result, it recommends that Atrazine should be used for sugarcane, orchard and rubber land, Glyphosate for non farming land and rubber land, Sulfometuron methyl for forest land, and 2, 4-D for maize land, respectively. Key words: Mikania micrantha, crop yield loss, plant community, chemical control, Yunnan Province.

Effects of sweet potato (Ipomoea batas) cultivation on the community composition and diversity of weeds in arid fields.

For developing ecological prevention and management techniques for invasive and dominant weed species, the screening and using of high value species with strong competitive ability (e.g., local food, native species and/or cash crops) have captured widely attention. To explore the effects of sweet potato (Ipomoea batas) cultivation on community composition and species diversity of weeds, the composition, density, importance value, species richness, diversity indices, and Pielou index were analyzed under five different cover scenarios (0%, 1–25%, 26–50%, 51–75, 76–100%). The study took place in arid cultivated fields in Jianshui County, Yunnan Province, China. A total of 25 weed species from 18 families were identified. Of these, four invasive species Ageratum conyzoides, Bidens pilosa, Eleusine indica, and Galinsoga parviflora and two native species, Digitaria sanguinalis and Portulaca oleracea had the highest population density and were most dominant. Population density and importance values of the six dominant weed species declined as sweet potato cover increased. A significant negative correlation was observed between importance values and sweet potato cover (P<0.05). Population density of two less dominant native species, Calystegia hederacea and Poa annua, increased significantly with increasing sweet potato cover. Similarly, the importance values for two additional native species Acalypha australis and Echinochloa crusgalli was positively correlated with sweet potato cover (R=0.964, R=0.891, P<0.05). Maximum values for species richness (23.5, 24.5), Simpson index (0.89, 0.85), Shannon-Wiener index (2.36, 2.35) and Pielou index (0.75, 0.73) corresponded to sweet potato cover ranges of 1–25% and 26–50% respectively. As sweet potato cover increased species richness and diversity values significantly declined. Overall, the results indicate that the cultivation of sweet po486 生 物 多 样 性 Biodiversity Science 第 22卷 tato alters the community composition and diversity of weeds limiting the occurrence of the dominant and invasive weed species. As a result, mid to low percent cover values should be considered an effective and ecologically-based weed management strategy to replace herbicide use in arid fields.