Environmentally friendly treatment alternatives to Bordeaux mixture for controlling bacterial apical necrosis (BAN) of mango.

Abstract

Bacterial apical necrosis (BAN), caused by the bacterium Pseudomonas syringae pv. syringae (Pss), is currently the most limiting disease affecting the mango crop in the Mediterranean area. The copper-based compound Bordeaux mixture (BM) is considered to be the conventional treatment against BAN, but it does not act as a bactericide. Alternative experimental treatments to BM that are compatible with organic farming were tested for their ability to control BAN disease. Field trials were conducted over six seasons in different mango orchards with natural infestation of Pss. The experimental treatments included applications of Silicon gel (a commercial formulation of aqueous potassium silicate), dicalcium phosphate, Kaolinite, and Ulmasud B (bentonite, powder); BMwas applied as the conventional treatment. During the first two seasons (small-scale trial, 2002–2004), all these experimental compounds were applied in order to select those treatments providing the greatest reduction of BAN symptoms. In the next three seasons (2005–2008), a semi-commercial scale trial was carried out with the best-performing treatments, resulting in the selection of Silicon gel. Finally, Silicon gel was tested in a commercial scale trial during the last season (2008–2009). Trees treated with Silicon gel showed significantly fewer necrotic buds and leaves, reaching disease levels very similar to those using the conventional treatment with BM. However, minor differences in P. syringae-like population levels were observed, as has been described in previous studies. The possible mode of action of the Silicon gel is discussed. Currently, the Silicon gel compound is undergoing the registration process for its commercial use in mango management in Spain.