Annual treatment with 1 lb/A of 2,4-D (2,4-dichlorophenoxyacetic acid) repeated for several years during mid- to late June gave excellent control of ironweed (Vernonia baldwinii). Later dates of treatment were not as effective. Mowing was not satisfactory as a weed control measure for ironweed. The populations in mowed plots in long-term experiments closely paralleled populations of untreated plots. Where numbers were reduced by spray treatment, recovery or reinfestation was comparatively slow. Quadrat counts were compared with visual estimation as methods of evaluating effects of treatments. The estimation method did not permit quantitative evaluation of year-to-year treatment or environmental effects.