Prospects for control of citrus canker with novel chemical compounds

Field trials conducted in Brazil demonstrate that even reduced rates of copper formulations (copper hydroxide, CH; copper oxychloride, COC) are consistently effective for control of canker [Xanthomonas axonopodis pv. citri (Xac)] on moderately susceptible orange varieties. Bactericides to replace and/or reduce copper could minimize potential risks of induced bacterial resistance, soil accumulation and environmental contamination. Alternative compounds with contact activity, including the fungicide famoxate (Dupont Crop Protection) and the antibiotic gentamicin (GWN 9350, Gowan Co.), are under field evaluation. At a south Florida canker quarantine facility, trials showed that gentamicin formulated for greater rain-fastness was effective for reducing disease on susceptible 'Pineapple' sweet orange and Swingle citrumelo seedlings over a 3-year period. On mid-season Pera sweet orange in Brazil, six applications of CH and COC at 0.5 of the label rate were effective in reducing canker on foliage, defoliation and fruit infection. Control was reduced at lower rates of CH (0.5 - , 0.25 - , 0.125 -); combination of the fungicide famoxate with the reduced rates of CH did not show greater control activity than the lower rates of CH alone.