To evaluate the efficiency of citrus canker (Xanthomonas axonopodis pv. citri) control in orchards, experiments were conducted in mature Washington Navel' orange in Concordia, Entre Rios, Argentina in 2002 - 2003, 2003 - 2004 and 2004 - 2005. Treatments consisted in a sequence of applications of cuprous oxide (NORDOX 75?)applied from the beginning of spring leaf flushing (end of August) to the time that fruit reached 5 to 6 cm in diameter (February). Treatments consisted in either 1 to 8 cuprous oxide applications compared a control with no copper. Early season copper applications were made with NORDOX 75? at 100 g/100 L (1 000mg/L)and later in the season with 75 g/100 L (750mg/L). In the first two applications of cuprous oxide treatments with and without NuFilm 17? were compared. Canker incidence was evaluated on fruits and on leaves from spring (October, November) and autumn flushes (end of February). A single application done at the beginning of flushing reduced canker incidence in fruit and spring leaves more than 50%. A second application performed 15 days later, reduced again canker incidence more than 50%. Best control on both tissues was achieved when 5 applications were done up to the end of November. Additional applications performed till the end of February did not improve canker control. Similar results were found for autumn leaves. These data suggest that copper effect on bacteria control may not be a straight contact effect. In addition, it was found that copper applications on spring leaves, protect them from greasy spot (Mycosphaerella citri) which is observed the following spring. Higher applications of copper up to 12 kg of metallic copper per ha. caused phytotoxicity on leaves.
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