Chemical control of bacterial citrus canker in lime in Thailand

Several chemicals, including Canoron registered (bacbicure, azole compound), Masbrane registered (antitranspirant compound), Funguran registered (copper hydroxide), Cupravit registered (copper oxychloride), Thianosan registered (thiram), and Phytomycin registered (streptomycin plus oxytetracyclin) were screened in laboratory tests for activity against Xanthomonas smithii subsp. citri (Xsc) and tested in greenhouse and field trials for control of bacterial citrus canker in Thailand. Using a paper disc agar-diffusion technique, Thianosan registered and Phytomycin registered were both highly effective in preventing growth of Xsc whereas the other chemicals showed little or no effect. Three treatments, Canoron registered , Thianosan registered , and Phytomycin registered reduced disease incidence in greenhouse tests using inoculated lime (C. aurantifolia cv. Pan Rum Pai) seedlings. Field trials using 5-year old lime trees in a grove in Phetchaburi province were conducted over a two year period from 1) Oct. 7-Nov. 17, 2004; 2) Nov. 10-Dec. 22, 2004; 3) July 26-Aug. 24, 2005; and 4) Oct 12-Nov. 2, 2005). Canoron registered and Cupravit registered significantly (5% level) reduced disease incidence by 23% and 26% over the water controls in experiments 1 and 4, respectively. No control was evident during experiments 2 or 3. Whereas heavy rains occurred during experiments 1 and 4 none occurred during experiments 2 and 3.