Tree-row-volume-based sprays of copper bactericide for control of citrus canker

Abstract

Commonly, pre-determined copper spray volumes are indiscriminately applied to citrus orchards of different ages and sizes for control of citrus canker (Xanthomonas citri subsp. citri) leading to a waste of resources, such as water, energy, and chemicals. This study evaluated the effectiveness of copper applied following the tree-row-volume (TRV) methodology for control of citrus canker on sweet orange trees. Treatment design was based on the theoretical runoff volumes previously determined for the exterior and interior of a citrus tree. The volumes 150 (standard), 100 (internal runoff point), 70 (intermediate) and 40 mL (external runoff point) of spray mixture/m3 of tree canopy were tested at the standard copper rate of 0.525 g metallic copper/L. Additionally, 70 and 40 mL/m3 were also tested with copper rate correction by leveling up the theoretical deposition of copper bactericide to that obtained with 100 mL/m3.Untreated control trees (UTC) were not sprayed with copper. Reduction of the spray volume did not affect disease control. While UTC trees presented a peak incidence of citrus canker on leaves of 30% in both years, copper-treated trees showed significantly lower peak incidences of 5–10%. Likewise, the average number of dropped fruits with citrus canker for the UTC was 2.0- to 1.5-fold higher than for copper treatments. At harvest, 30% of fruits from the UTC trees showed citrus canker symptoms. Conversely, only 3.3–9.8% of the fruits from the copper treatments were symptomatic. Moreover, using 40 mL/m3 without adjusting the amount of metallic copper diminished disease control efficiency on leaves. Reduction of spray costs and water needs amounted to 40 and 73%, respectively. In addition to keeping effectiveness of disease control and being more environmentally friendly, the adaptation of the spray volumes and copper rates to the TRV may contribute to reducing production costs.