Strongid is NOT effective. The Oxibendazoles and Fenbendazole dewormers show very high resistance in adult horses. Not all vets are up on current dewormer research
I rotate using Pyrantel Promate, Ivermextin, and Moxidectin, including one deworming a year using a product that contains Praziquantel (Equimax or Quest Plus) to take care of tape worms. I'm in Arkansas, our weather and parasites are similar to Georgia. This is my deworming schedule and it has worked very well. I use rendaivu.com (a FREE web site) to keep up with scheduling and what-not.
Jan 1: Ivermectin + Praziquantel
Mar 1: Pyrantel, double dose (Exodus Multi Dose or TapeCare+)
Apr 1: Moxidectin
July 1: Ivermectin
Sept 1: Pyrantel, double dose (Exodus Multi Dose or TapeCare+)
Oct 1: Moxidectin
The dates are based on reemergence cycles of the worms. You do not need to deworm more frequently than recommended, unless your horse is very susceptible to parasites.