Development and validation of a fungicide scoring system for management of late season soybean diseases in Argentina Marcelo Carmona a, * , Francisco Sautua a , Susana Perelman b , Marcela Gally a , Erlei Melo Reis c a Department of Plant Pathology, Faculty of Agronomy, University of Buenos Aires, Av. San Martín 4453, Capital Federal 1417, Argentina b Department of Quantitative Methods and Information Systems, IFEVA/Faculty of Agronomy, University of Buenos Aires/CONICET, Argentina c OR Melhoramento de Sementes Ltda, Passo Fundo, RS, Brazil article info Article history: Received 28 September 2014 Received in revised form 16 January 2015 Accepted 25 January 2015 Available online xxx Keywords: Septoria glycines Cercospora kikuchii Late season soybean diseases Fungicide application timing Scoring system abstract The use of foliar fungicides is a common disease control practice among soybean producers around the world, yet there is still no clear understanding about the timing and opportunity of fungicide applica- tions to manage late season diseases (LSD) in soybean crops. The unnecessary use of fungicides in extended areas increases production costs, risk of resistance and risk of negative environmental impact. The objective of this study was to develop and validate a scoring system to guide the application of fungicides in soybean crops to manage LSDs in Argentina, with special reference to Septoria brown spot and Cercospora leaf blight. To develop the scoring system, a risk matrix with weighted epidemiological risk factors was developed based on previous research data. The scoring system recommends application of foliar fungicides based on the total points accumulated from the risk factors. Scoring greater than 33 indicates a higher probability of obtaining a positive yield response, whereas scoring below 23 indicates no expected response and thus no need for fungicide applications. Intermediate values indicate that the application of fungicides would produce uncertain results thus detailed analysis of risk factors would be required. To validate the scoring system, 19 field trials were carried out over five growing seasons in three Argentinian provinces. The fungicide used in all trials was a mixture of a quinone outside inhibitor and a demethylation inhibitor fungicide. In most cases, the scoring system resulted in appropriate decisions to apply the fungicide within the so-called “window of opportunity”, which lies between the R3 and R5 soybean developmental stages. The greatest yield responses were achieved when the scoring system recommended the fungicide application at R3 or R4 or R5, depending on the obtained sum of points. In all cases, except when the scoring system recommended no application of the fungicide, disease severity values were significantly greater in untreated than in treated plants. Regarding net income, phenology- based applications showed negative margins in cases where the scoring system recommended no ap- plications, demonstrating that in such situations the use of fungicide caused losses rather than yield advantages. In contrast, when the scoring system recommended the application of fungicide regardless of timing (R3, R4 or R5), net margins were always positive and generally provided a higher income. The scoring system presented in this study can be a valuable tool to reduce the number of fungicide appli- cations in soybean crops, especially in seasons when conditions for LSD development are not favorable. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction Late season soybean diseases (LSDs), a combination of various diseases that affect soybean leaves, stems, pods and seeds, cause premature senescence and reduce grain yield and seed quality (Hartman et al., 1999; Wrather et al., 2004; Sweets et al., 2008). In the Pampean Region of Argentina, the main LSDs are Septoria brown spot (Septoria glycines Hemmi), Cercospora leaf blight and purple stain (Cercospora kikuchii T. Matsumoto & Tomoyasu), pod and stem blight (Phomopsis sojae (Lehman) Wehm) and anthrac- nose [Glomerella glycines (Hori) Lehman & Wolf; Colletotrichum truncatum (Schw.) Andrews & WD Moore], with S. glycines and C. kikuchii being the prevalent pathogens (Carmona et al., 2010). * Corresponding author. E-mail address: carmonam@agro.uba.ar (M. Carmona). Contents lists available at ScienceDirect Crop Protection journal homepage: www.elsevier.com/locate/cropro http://dx.doi.org/10.1016/j.cropro.2015.01.019 0261-2194/© 2015 Elsevier Ltd. All rights reserved. Crop Protection xxx (2015) 1e9 Please cite this article in press as: Carmona, M., et al., Development and validation of a fungicide scoring system for management of late season soybean diseases in Argentina, Crop Protection (2015), http://dx.doi.org/10.1016/j.cropro.2015.01.019