Integrated Management Technology Of Water Hyacinth In Its "Wilting In Winter And Blooming In Summer" Regions

The water hyacinth, Eichhornia crassipes (Martius) Solms-Laubach, is a cosmopolitan notorious aquatic weed in 40°N~45°S regions. It has invaded Africa, Asia, North America and Oceania, occurs in at least 62 countries. The invasion of water hyacinth has become a serious ecological and economic concern in the international community as well as in China. Because it originated in the state of Amazonas, Brazil, spread to other regions of South America, and was carried by humans throughout the tropics and sub-tropics. At present, solutions for controlling the spread of water hyacinth are divided into three general categories: physical, chemical and biological control. Biological control has been promoted as the best means for controlling water hyacinth and currently is an important area of research.. However, most of these research was carried on the tropics and sub-tropics area where water hyacinth could grow throughout year, our knowledge and understanding of the biology and ecology of water hyacinth in northerly sub-tropics and some temperate zone (28°N) is very little. In this region, such as Ningbo, China (28°51 ~30°33 N), as the lower temperature in winter, water hyacinth grow very fast from later spring to autumn, but wilt in winter. In this paper, we researched the growth and development characteristic and effectively integrated management technology of water hyacinth in this region.First, we found three growth and development characteristic of water hyacinth in Ningbo: (1) It grow very fast from May to October every year, but died in winter because the lower temperature. In the early spring, the mortality of water hyacinth was 82.7% to 99.5%. The density > height and biomass of water hyacinth decreased 63.8%, 87.9%, and 74.5%, respectively, comparing to these in summer. (2) There was a significant relationship between the low temperature in winter and the situation of water hyacinth in next year. If the temperature was lower than 0℃ and keep a long time, the water hyacinth would occur later and less biomass in next spring. (3) It could sexual reproduction by seeds in autumn and agamogenesis by buds and stolons during March to October. In next spring, the seeds germinated at a wet place upon water surface when the temperature higher than 23℃. Then, we summarized a danger analyze patternfor monitor water hyacinth in sensitivity season and sensitivity water area in Ningbo.Second, we introduced two water hyacinth biological control agents (water hyacinth weevils) (Neochetina eichhomiae & Neochetina bruchi) and research into the weevil's host range, the effect on control water hyacinth, the rules of survive in the winter, the methods of promoting weevil population development, and the biological control technique in Ningbo district. After change the normal method which release the weevils adults in water hyacinth biocontrol area and let the weevils population develop in 3 to 5 years to control the water hyacinth, we created the "raise the weevils in greenhouse for overwinter", "release the complex population of water hyacinth weevils (the weevils in different age structure) with their parasitic water hyacinth plants in spring". It could make the population of weevils develop faster and raise controlling effects more than 50% in three months.Third, we compared 18 kinds of herbicide and selected 3 kinds of herbicides, which could kill the water hyacinth plants fast and safely. Meanwhile, we tested to using herbicide two times and using it in autumn to decrease the number of overwintering plants. It could significant decrease dosage of herbicides and increase the effect of them.Fourth, for harvesting the water hyacinth more effectively, we developed to harvesting it in early spring time when most of the water hyacinth plants had died in winter and early summer time when the population of water hyacinth was very small, and created "floating bamboo bars" and "plastics buoy net" to gather the water hyacinth plants and harvest it effectively. After using all of these technique and equipment, we had increased the physical...