The plant pathogenic fungus Albugo tragopogi (Pers.) S. F. Gray (“white rust”), isolated from a local population of common ragweed (Ambrosia artemisiifolia L.) and inoculated into ragweed seedlings at the two-leaf stage, reduced pollen production by 99%, seed production by 98%, and top weight by 79% of plants that developed systemic disease symptoms while growing in a controlled environment. However, only 14% of the inoculated plants developed systemic symptoms. A convenient method of inoculating leaves of seedling plants with zoospores of a fungus is described.
