Comparisons of drench and surface spray treatments to disinfest balled and burlapped nursery stock of red imported fire ants

The Federal Imported Fire Ant Quarantine (FIFAQ) restricts the movement of articles that can harbor fire ants beyond established infested areas in the USA. Balled and burlapped (B&B) nursery stock, which are plants with soil containing root balls wrapped in burlap, are of particular concern because the approved FIFAQ treatment of immersing the entire root ball into a solution of chlorpyriphos or bifenthrin insecticide is expensive and impractical for growers. Another FIFAQ approved treatment is the complete drenching of root balls with chlorpyrifos. However, this treatment, while more practical for growers, has inconsistently disinfested fire ants from large (e.g., 24-inch diameter) root balls. We compared the efficacy of drench applications of chlorpyrifos, two pyrethroid insecticides, and a surface spray application of dinotefuran to disinfest red imported fire ants, Solenopsis Invicta, from B&B root balls. Because growers indicated they would not ship plants obviously infested with large colonies of fire ants, we infested large diameter B&B nursery stock with small S. invicta colonies prior to treatment. Two weeks after treatment, root balls were destructively sampled to determine the presence of live S. invicta. Live fire ants were not detected in any (N=10) of the root balls treated with the surface spray of dinotefuran. In contrast, drench applications with the pyrethroids bifenthrin and lambda cyhalothrin, with chlorpyrifos, and with water (control) remained infested in 30, 50, 80, and 50% (N=10) of the root balls, respectively.