We were very fortunate to have Bridget Stice, Polk County Agricultural Extension Agent, speak to us at our May meeting. She identified plants that members brought in, handed out posters of poisonous plants, and recommended containment and eradication practices. Polk County residents can email picture of plants to Bridget (bcarlis@ufl.edu) for identification or, with enough notice, have her come to evaluate their own property.
Attached are 2 documents Bridget gave members, which (among other excellent information) are available at http://edis.ifas.ufl.edu/.
Weed mgt in oastures and rangeland 2018–IFA
Screeping indigo, a poisonous plant of concern in Florida pastures–IFAS
Bridgett also 
Florida Sport Horse Club 