Picture of the Leaves
Source: Wunderlin, R. P., and B. F. Hansen. 2008. Atlas of Florida Vascular Plants (http://florida.plantatlas.usf.edu/).[S. M. Landry and K. N. Campbell (application development), USF Water Institute.] Institute for Systematic Botany, University of South Florida, Tampa.
This weed can be controlled rather easily with the right herbicide. The following table clearly shows that Pasturegard HL, GrazonNext HL, and Remedy Ultra were the most effective for controlling the weed. Although glyphosate is the most cost effective, it does not completely control the weed and it will leave bare patches on the treated area.
Dr. Sellers and Dr. Ferrell (UF IFAS Weed Scientists) have this to say about the chemical controls: “It is our recommendation that GrazonNext HL, Remedy Ultra (or comparable triclopyr ester product), or Pasturegard HL be used for effective control of fireweed. These herbicides can be applied any time of year to warm-season forage grasses. There are no grazing restrictions for beef cattle with these herbicides, but lactating dairy animals must be removed for 0 and 14 days with GrazonNext HL and Remedy Ultra, respectively, and one season for Pasturegard HL.”

Mowing may seem like a good way to control this weed, but unfortunately it results in smaller plants with more stinging hairs. Seed can adhere to the mower blades and be dispersed to non-affected areas.
Source:ufl.edu