The antimicrobial activity of acetamiprid, imidacloprid (IMI), and thiamethoxam was tested in vitro against Xanthomonas citri subsp. citri (Xcc) isolates. Plants of 'Valencia' sweet orange were treated by drenching with IMI and infiltrated with Xcc suspension in the greenhouse. The neonicotinoids showed no in vitro antimicrobial effect against Xcc. Plants of 'Valencia' sweet orange treated with IMI showed fewer and smaller lesions of citrus canker, as well as changes in the levels of macro and micronutrients when compared with control plants. Reductions in the incidence of citrus canker between 10% and 70% were observed in plants treated with IMI. Disease incidence was significantly lower in plants treated with 1.5 g and 3.0 g of IMI (a.i.), while a significant reduction of up to 4.7 log units in the bacterial population was observed in plants treated with 3.0 g IMI (a.i.). Plants treated with IMI at the same time of inoculation also showed significant reduction in the bacterial population and in the number of citrus canker lesions.
Xanthomonas citri subsp. citri; acetamiprid; citrus; imidacloprid; resistance induction; thiamethoxam
