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Aims:  The study provides useful information on the temporal population dynamics of the biological control agent, Penicillium frequentans, after its applications against brown rot in orchards. Methods and Results:  Population dynamics of P. frequentans were studied on peach flower and fruit surfaces after different field treatments. Eight experiments were carried out in commercial peach orchards in Spain, over four growing seasons from 2002 to 2005. Six different formulated P. frequentans conidia were applied four to six times from blossom to harvest and P. frequentans population sizes were monitored using conidial numbers and colony forming units (CFU) per flower or fruit. A consistent population of P. frequentans, ranging from 105 to 106 number of conidia or 103 to 104 CFU of P. frequentans per flower or fruit, was obtained. Colonization of peach surfaces by all P. frequentans formulation are similar and it appears to follow a general pattern: (i) higher colonization of fruits at preharvest than on the flowers at bloom; (ii) high populations just after treatments, especially after preharvest treatments; and (iii) a slight decline between treatments, especially in cool and moist springs. The exponential model was the most appropriate for fitting and comparing the P. frequentans dynamic populations on peaches and nectarines over time. The linearization of the P. frequentans population curve was essential to determine dynamic population and for population levels forecast. A positive relationship between number of blossom and preharvest applications, temperature, relative humidity and dynamic of P. frequentans population applied on peaches was studied using a multiple regression model. Conclusions:  Blossom and preharvest applications were the most important spray times for obtaining the highest population of P. frequentans on peach surfaces. Significance and Impact of the Study:  The study provides useful information on dynamic P. frequentans population and its effects on the brown rot biocontrol.

Different treatments based on the biocontrol agent (BCA) Bacillus amyloliquefaciens CPA-8 to control brown rot under field conditions were evaluated as alternative to chemical applications. As part of a well-designed disease program that enables the integration of BCAs into cropping systems, testing of the sensitivity of Monilinia laxa and Monilinia fructicola at different doses of CPA-8 were conducted in stone fruit. CPA-8 dose of 10 7 CFU mL-1 reduced more than 60.0 and 75.5 % of brown rot incidence and severity, respectively. Once in the orchard, different degree of biocontrol activity was obtained depending on the inoculum pressure, which was mainly associated with meteorological conditions. Under drastic disease pressure, neither CPA-8 treatment nor the chemicals controlled the disease at harvest and only the chemical treatment reduced postharvest brown rot incidence. However, when Monilinia spp. incidence was close to the standard levels recorded in the area, treatments based on CPA-8 formulations proved to be efficacious. At harvest, BA3, BA4 treatments (CPA-8 optimised products) and PF+BA3 treatment (CPA-8 combined with Penicillium frequentans) reduced Monilinia spp. incidence compared to the control (54.7-64.1 %) although less than the chemicals (90.6 %). At postharvest, almost all CPA-8-based treatments (except PF+BA3) controlled the pathogen with BA4 treatment being as much effective as the chemicals (50.3 % of disease reduction). Finally, the population dynamics of CPA-8 on treated fruit surface remained after treatment application, at harvest and at postharvest shelf-life (>10 4 CFU cm-2). This study highlights the potential of B. amyloliquefaciens CPA-8 as alternative or complementary strategies to control Monilinia spp.