Chemical Control Technology Of Weeds On Dike Of Yangtze River In Jingzhou, Hubei Province

This thesis studies weeds in dike lawns and investigates the variety and rules for seasonal changes of weeds on the main screen dike (8+000—10+000) of Jinwan management segment in Honghu flood diversion area as well as the composition of seeds in the soil. It also offers a preliminary study on weed control with chemical herbicides, which provides guidance on theoretical level to preventing and removing weeds on dike lawns through a chemical approach. The conclusions of the thesis are as follows:1. A study of weeds in bermuda grass and centipede grass on the main screen dike shows there are81kinds of weeds, which can be categorized into29families. Gramineous weeds make the biggest portion, with15kinds and accounting for18.52%. Compositae weeds come the second, with14kinds and accounting for17.28%. There are4kinds under cruciferae, leguminosae, euphorbiaceae, and labiatae,3kinds under caryophyllaceae, rosaceae, umbelliferae and sedge family, two kinds under polygonaceae, solanaceae, scrophulariae, plantaginaceae and rubiaceae, respectively. The other families have one kind of weed each.64kinds sprout in spring, with pedunculate tigonotis, hydrocotyle sibthorpioides, oxalis triangularis as dominant species;53kinds sprout in summer, with copperleaf, crabgrass as dominant species;48kinds sprout in autumn, with copperleaf, oxalis triangularis, horsetail, veronica persica as dominant species;18kinds sprout in winter, with dandelion, hydrocotyle sibthorpioides, oxalis triangularis, chinese violet, roegneria, cerastium caespitosum, bedstraw, cephalanoplos as dominant species. The variety of weeds decreases from spring to winter. So do the variety indexes such as E. Simpson and C. Shannon-W. Wiener. But E. Pielou uniformity coefficient decreases from spring to autumn and then rises in winter.2. A study of seed sprouting in soil seed banks indicates that a total of2411strains sprout in the0-5cm soil layer, with63kinds of weeds belonging to24families.292strains sprout in the5-10cm soil layer, with34kinds of weeds belonging to18families. About90%of weed seeds can be found in the0-5cm soil layer. It is estimated that the weed seeds density in the0-5cm soil layer is2009.17grains/m2, and in the5-10cm soil layer is243.33grains/m2. The sprouting reaches its first climax period in the second week, with a sprouting ratio of16.72%. Then the ratio drops until the second climax period comes in the fourteenth week. This process lasts for six week. Sprouting in the0-5cm soil layer stops in the25th week and that in the5-10cm soil layer stops in the22nd week.3. Weeds control with a chemical approach (1) Experiment was done to compare the effectiveness of4pre-emergence herbicides, i.e., trifluralin, dual gold, alachlor and acetochlor. High-concentration dual gold works best on summer-and-autumn weeds, with an average prevention success rate of82.58%. It works best on winter-and-spring weeds as well, with the highest effectiveness achieved when it is applied between September10th to20th.(2) When broad leaf weed herbicides are used in regular concentration, the ranking of average effectiveness is as follows:Fluroxypyr (74.80%)>2,4-DA(70.89%)>2M-4X (44.02%). The effectiveness of high-concentration broad leaf weed herbicides, expect for horsetail, is100%. When herbicide for gramineous weeds is used, the average effectiveness of quizalofop-p-ethyl and haloxyfop-P-methyl of high concentration is above70%, but turf grass withers and stops to grow. When applied in high concentration, the effectiveness reaches100%, but turf grass dies as herbicide concentration rises.(3) An experiment was carried out which makes use of3factors5levels orthogonal rotatable central composite design and seeks for the most effective mix of2,4-DA, fluroxypyr and quizalofop-p-ethyl by building a mathematical model with the effectiveness of weed control as objective function. The experiment shows there are44combinations that have effectiveness higher than90%. In the distribution range of optimum combination (95%), the actual amount range of the three herbicides are0.062-0.068mL/m2,0.098～0.102mL/m2and0.058～0.070mL/m2, respectively.