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Comparison of Application Methods of Systemic Fungicides to Suppress Branch Cankers in Clementine Trees Caused by Phytophthora citrophthora

Since 2002, considerable losses of Clementine trees (Citrus clementina) have been observed in Spain due to Phytophthora branch canker of citrus caused by Phytophthora citrophthora. Due to the low efficiency of the available cultural and genetic control measures, application of fungicides is required for economic management of the disease. Fosetyl-Al, metalaxyl, and its enantiomer mefenoxam are the only systemic fungicides registered for control of Phytophthora diseases in Spain. However, their efficacy has not been tested against Phytophthora branch canker. Greenhouse and field experiments were conducted for 3 years in Spain to evaluate the ability of these fungicides and application methods to reduce lesion expansion. Nevertheless, with the inoculation technique used, it was not possible to evaluate the protective activity of fungicides, which can play an important role in their performance under field conditions. None of the fungicide treatments inhibited lesion expansion when applications were made on a curative basis. The residual effect was better on young than on mature trees. Paint treatments were generally more effective in reducing lesion expansion that drip chemigation or foliar sprays. However, this application method is laborious and becomes uneconomical in Spain. Trunk and branch sprays as well as long-term programs of foliar sprays or drip chemigation for control of spring and autumn infections are proposed as targets for future research.