Study on chemical control to Eupatorium odoratum in karst area

Pingguo County in Guangxi has been seriously invaded by Eupatorium odoratum for more than ten years. Three herbicides (paraquat, glyphosate and glyphosate mixed with 2, 4-D)at three grades of concentration 1%(high), 0.5% (middle) and 0.25%(low) respectively are used to control E. odoratum in the area seriously invaded by the weed. The results prove that five days after spraying the herbicides, all of the E. odoratum dried-up under every treatment of the herbicide paraquat with each grade of concentration; while 2/3 of the leaves dried-up and stems semi-dried-up under the high concentration of glyphosate, as well as under high and middle concentration of glyphosate mixed with 2, 4-D. Thirty days after spraying the herbicide, the mortality of the weed is 77% under low concentration of paraquat and up to 100% under high concentration; and the density of new seedlings under each treatment is significantly lower than that in control sample area. The mortalities of the weeds under the treatment of glyphosate and glyphosate mixed with 2, 4-D are 33% at low concentration and about 50% at high concentration, but the densities of new seedlings under these treatments have no significant difference with the control sample. According to the above results, paraquat at different concentration exhibits more efficacy than glyphosate and glyphosate mixed with 2, 4-D. This herbicide can obviously influence the soil seed bank of the E. odoratum weed. So it is better to select paraquat as herbicide in the environments where E. odoratum weed formed dominant community. Glyphosate and glyphosate mixed with 2, 4-Dat comparatively high concentration, being able to prevent and kill most E. odoratum weed, should be used in concomitant community of E. odoratum weed, such as in farmland or orchard.