Red leaf blotch (RLB) of almond, caused by Polystigma amygdalinum, is an important foliar disease of this nut tree in the Mediterranean basin and Middle East regions. In recent years, the incidence of this disease has increased in Spain, corresponding to increases in the area of newly planted orchards and the use of susceptible cultivars. In 2009, an experimental orchard including 21 almond cultivars was planted at Les Borges Blanques, Lleida, in northeastern Spain. No fungicide treatments were applied during the 10-year experimental period (2009 to 2018) in order to allow natural disease development. Cultivar susceptibility to RLB was assessed each year, from 2011 to 2018, through visual observations of symptoms in naturally infected trees. The experimental results led us to classify the cultivars into five susceptibility groups. The most susceptible were Tarraco, Guara, Tuono, Marinada, Desmayo Largueta, and Soleta, whereas Mardía was the most tolerant. The annual incidence of disease was positively correlated with accumulated rainfall in spring, and especially in April, while it was negatively correlated with high spring and summer temperatures, especially in May. These findings could be used to improve disease management strategies by identifying the most susceptible cultivars and improving the timing of fungicide application.

Red leaf blotch (RLB) disease of almond, caused by Polystigma amygdalinum, is an important foliar disease in most production regions of the Mediterranean basin and the Middle East because severe infections may cause a premature defoliation of the tree. Some key aspects on the epidemiology of P. amygdalinum were studied in multiyear trials in two almond-growing regions in Spain, which included the seasonal development of perithecia and production and germination of ascospores along with the disease incubation and plant infectivity periods. Our results showed that primary inoculum was available in extended periods (January to August). Significant differences in ascospore amounts among regions, higher in the southern Andalusia and lower in the northern Catalonia, and years of study were detected. The factors geographical location, sampling period, and evaluation year were found significant on the development of P. amygdalinum perithecia. Variable ascospore germination rates were observed from April to July: >15% but rarely exceeding 30%. The RLB infectivity period in Catalonia extended from March to mid-June, whereas in Andalusia it was from March to May. The incubation period was mainly in a range of 5 to 10 weeks in Catalonia. The environmental conditions of October to January influence the available ascospore amounts in the next season. RLB infection occurs in spring to summer when mean temperatures are in the range 10 to 20°C. These results represent the first step in developing a prediction model of the disease that might serve as a tool for the control of RLB.

Pecan trees form a symbiotic relationship with ectomycorrhizal fungi (ECM), which actively provide nutrition to the roots and protect them from phytopathogens. Although these trees originated in the southern United States and northern Mexico, information on their root colonization by ECM is insufficient in terms of a representative number of samples, both in these regions and worldwide. Therefore, the objectives of this study were to determine the percentage of ectomycorrhizal colonization (ECM) of pecan trees of different ages in conventional and organic agronomic orchards and to identify ectomycorrhizal sporocarps, both morphologically and molecularly. The rhizospheric soil properties and the ECM percentages were analyzed for 14 Western variety pecan tree orchards between 3 and 48 years of age and grouped according to the agronomic management method. DNA extraction, internal transcribed spacer amplification, and sequencing were conducted on the fungal macroforms. The ECM colonization percentage fluctuated between 31.44 and 59.89%. Soils with low phosphorus content showed higher ECM colonization. The ECM concentrations were relatively homogeneous in relation to the ages of the trees, and organic matter content did not affect the percentage of ECM colonization. The highest ECM percentages occurred with the sandy clay crumb texture soil, with an average of 55% ECM, followed by sandy clay loam soils with 49.5%. The Pisolithus arenarius and Pisolithus tinctorius fungi were molecularly identified from sporocarps associated with pecan trees. This is the first study that reports Pisolithus arenarius as being associated with this tree.

BACKGROUND: Almond blossom blight, caused by Monilinia spp., is a notable fungal disease associated with intensified crop management practices. In this study, we aimed to investigate the epidemiology of Monilinia spp. on almonds in two orchards in the Ebro Valley, with a focus on (i) primary inoculum sources through sampling of affected mummified fruiting structures from trees and the ground before blooming; (ii) secondary inoculum sources postblooming; and (iii) disease dynamics throughout the season in relation to meteorological data. RESULTS: Monilinia laxa was the primary species affecting almonds in the Ebro Valley. Furthermore, early‐stage mummified fruiting structures frequently adhered to branches (3.8 log conidia/mummified fruiting structure), whereas late‐stage mummified fruiting structures were predominantly found on the ground. Additionally, cankers present before blooming (6.0 × 10 ² and 1.4 × 10 ³ conidia/canker) served as primary inoculum sources. Inoculum incidence and concentration were significantly higher in late‐stage fruits (50–100%, 8.5 × 10 ³ –2.5 × 10 ⁵ conidia/plant organ) than those in flowers (20–30%, 2.0–4.0 × 10 ³ conidia/plant organ) or those in postblooming cankers (1.0 × 10 ² –1.8 × 10 ³ conidia/canker). Infection dynamics of blossom blight in both orchards peaked during the last third of April under favorable meteorological conditions, specifically within the 10 days preceding the assessments. Significant correlations were found between infections progression and meteorological parameters, including temperature, relative humidity, rainfall and leaf wetness. CONCLUSION: These findings provide critical insights into sustainable disease management practices and the optimal timing of protective measures against blossom blight. © 2025 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.