Effects Of Biological And Chemical Control Agents On Water Hyacinth, Eichhornia Crassipes

Water hyacinth was one of the most notorious weeds in the world because it caused environmental problems and threatens inhabitants where it growed. So, a solution to the problems caused by water hyacinth was urgently required. The control measures tested mainly consisted of mechanical control (hand-pulling), chemical controls (herbicides) and biological controls (weevils and pathogens). Control with herbicides, such as glyphosate and 2, 4-D, has been effective. However, both of these are costly, and there effects are only temporary. Biological agents have reduced the weed problem in many countries, but only where water hyacinth does not erupt badly. Facing these disadvantages, we utilized a two-discipline integrated-control approach rather than a single control method to control water hyacinth. This paper shows the effects of each combination of two agents and of the three control agents (herbicides, weevils and pathogens) and their joint impact against water hyacinth. Major results and findings were as follows:1 Survey of the growth of water hyacinth in the fieldThe data show that, when the mean number of adults was more than three per plant, the parameters: the length of the longest petiole, fresh weight, root length and the number of daughters per plant were significantly different (P>0.05) compared to when the mean number of adults was than less one per plant. However, water hyacinth still covered the entire water surface.2 Joint control technique of herbicides and weevils against water hyacinthThe death rates indicate that both herbicides (glyphosate and butyl 2,4-dichlorophenoxy acetate) had very low toxicity. The highest death rates were 6.67% and 10%, respectively. Glyphosate inhibited the feeding of weevils, but the feeding rate was accelerated when the concentration of butyl 2, 4-dichlorophenoxy acetate was below 1,433 mg·L-1; the highest feeding rate was 124 mm2/d. Two weevils per plant combined with 200 mg·L-1 of glyphosate effectively controlled water hyacinth, and 15 days after the glyphosate was sprayed, the death rate was 100%. Four weevils per plant and 46 mg·L-1 of butyl 2, 4-dichlorophenoxy acetate also effectively controlled water hyacinth, and 10 days after spraying, the death rate was 90%.3 Joint control technique of pathogens and weevils against water hyacinthThe pathogen Alternaria sp. WH56 was nontoxic against weevils, but the weevils did not eat the leaves containing them. The results confirmed that using the weevils and pathogen together to control water hyacinth worked better than treatments with the biological agent alone.4 Joint control technique of herbicides and pathogens against water hyacinthThere was significant difference (P>0.05) between the impact of Alternaria sp. WH56 that invaded intact leaves of water hyacinth compared with already wounded on the plant. Both herbicides inhibited the pathogen's growth, with EC50 of 157 mg·L-1 and 2, 288 mg·L-1, respectively. Control of water hyacinth using Alternaria sp. WH56 and herbicides together was not successful, which proves that the herbicides and Alternaria sp. WH56 are not compatible. The results confirm that the use of herbicides and pathogens together to control water hyacinth performs worse than treating with the biological agent alone.