Chemical control of dieback and mango malformation in a semiarid region

Abstract

The São Francisco Sub medium Valley is a great mango exporter in Brazil. In this semiarid region, diseases such as dieback and mango malformation have reduced the production of this crop. In this work the effectiveness of different active ingredients (flutriafol, methyl-thiophanate, copper hydroxide and fluxapyroxad mixed with pyraclostrobin) was assessed for the control of these diseases in a mango orchard. Monthly assessments of disease incidence were carried out. There was a difference among treatments for the two diseases studied, with flutriafol as the most effective fungicide against dieback and, for the malformation, the mixture of fluxapyroxad and pyraclostrobin and methyl-thiophanate showed the best results. The mango (Mangifera indica) crop has a great importance in the submedium region of the São Francisco valley in Brazil. In 2021, mango was the most exported fruit considering the financial rank, with a total of US$ 248 million exported (KIST et al., 2022). The semiarid climate of this region is unfavorable to most mango diseases. Nonetheless, dieback and malformation diseases, caused by fungi belonging to Botryosphaeriaceae family and Fusarium genus, respectively, are not affected by this climate. Therefore, this study aimed to assess the effectiveness of four fungicides with different action modes in dieback and malformation control, two most important mango diseases in semiarid regions. The experiment began in July 2019 in a "Tommy Atkins" mango orchard located in the semiarid region of Petrolina, state of Pernambuco, Brazil. The orchard consisted of 10-year-old trees in a spacing of 8 × 6 m. Irrigation system was done by microsprinkler and each plant received 105 and 220 L of water per day in vegetative and flowering stages, respectively. The experiment was carried out in a randomized block design, with five treatments consisting of four fungicides and a control treatment, with eight replicates (blocks) per treatment. Each block had eight mango trees and the four central trees were used as experimental replicates. Treatments consisted of the following fungicides and rates, according to manufacturer recommendation: flutriafol (0.75 mL·L-1 , Tenaz), fluxapyroxad and pyraclostrobin mixture (0.4 mL·L-1 , Orkestra), methyl-thiophanate (0.7 g·L-1 , Cercobin), copper hydroxide (0.25 g·L-1 , Kocide) and the control (trees without any fungicide spray). Fungicide sprays began after first pruning, and were performed every 14 days until fruit set, totalizing 18 sprays. These sprays were conducted by a vertical bar sprayer model Condor 600 M12 (Jacto) using only one side of the bar, and, consequently, a side of the row being sprayed at a time. Each bar contained eight nozzles spacing 0.35 m from each other. The spray tip used was hollow-nozzle, model J4-2 (Jacto), with a flow of 1.64 L·min-1 in a working pressure of 150 lb·pol-2 and a tractor speed of 6.3 km·h-1. The pH from fungicide spray solution was measured using a paper tape (Macherey-Nagel). The solution pH was adjusted to 6.5 for the treatment with copper hydroxide and to 5.0 for the other fungicides using a pH reducer (Redufol),