Response to sublethal herbicide application in early growth of seven Xanthium strumarium populations

Seven populations of Xanthium strumarium L. collected from wetlands and arable fields were examined for their responses to three levels of bentazon application. Significant differences were observed among populations for all traits measured. Contrasts between the wetland and arable populations indicated significant differences in some traits, especially the length and width of the fifth internode. These measurements are closely related to plant biomass, and they were reduced greatly in the wetland populations after bentazon treatment. However, an overall comparison using canonical discriminant analysis failed to show differences between the wetland and arable populations, suggesting that differences in response to herbicide between the two ecotypes may be due to changes in a few traits relating to fitness. Key words: Growth, weed, herbicide, bentazon, cocklebur, Xanthium strumarium