Field susceptibility of almond cultivars to the four most common aerial fungal diseases in southern Spain

From 2004 to 2012, the incidence and severity of the four most common almond aerial diseases were evaluated in ten experimental fields in the main almond-growing areas of Andalusia, southern Spain. The studied experimental fields were representative of the different geographic locations, agronomic characteristics and farming systems in Andalusia. A total of 14 early-flowering and 26 late-flowering cultivars (cvs.) currently grown in the new almond plantings of Andalusia and the Mediterranean basin were evaluated. The incidences of red leaf blotch (RLB), shot hole (SH), blossom blight (BB), and leaf curl (LC), which were caused by Polystigma amygdalinum, Thyrostroma carpophilum, Monilia laxa and Taphrina deformans, respectively, were monitored in each field and year. RLB was the most prevalent disease, although its severity varied markedly among fields and years. BB caused the higher outbreaks, but this was only the case when rainfall coincided with flowering, and fungicide treatments were not applied. The early-flowering cvs. were more affected than the late-flowering cvs. by BB, although most of the early-flowering cvs. were less susceptible than the reference cv. Marcona to BB. However, 'Marcona' was less susceptible than most of the early-flowering cvs. to RLB. Among the late-flowering cvs., the reference cv. Guara was susceptible to the four monitored diseases. The responses of the cvs. to the diseases varied markedly among fields and years, with significant differences among cvs. for all diseases. This work represents the first study to evaluate a broad range of almond cvs. infected with the main almond foliar diseases in natural field conditions, making an important contribution to the understanding of varietal susceptibility of almonds to four significant foliar diseases. Moreover, this study highlights the need to consider cultivar resistance in the development and selection of plant material for new almond plantings and in integrated pest management.