Evaluation of foliage-applied fertilizers and fungicides for controlling soybean late season diseases during two growing seasons in Tucumán, Argentina

DE LISI, V.; GONZALEZ, V.; REZNIKOV, S.; STEGMAYER, C.A.; HENRIQUEZ, D.D.; DEVANI, M.R.; PLOPER, L.D.

Durban

Congreso; World Soybean Research Conference IX (WSRC IX); 2013

Protein Research Foundation

Diseases are among the biotic factors that reduce soybean yield in the province of Tucumán, located in northwestern Argentina (NWA). Continued monocropping and no-tillage systems, practices widely used at present in soybean production, have been related with the escalation of many of the disease problems that have occurred in recent years, including the ‘late season disease complex’, a combination of various diseases that affect stems, leaves, pods, and seeds, causing a premature senescence and lowering yield and seed quality. The main diseases included in this complex are brown spot (Septoria glycines), Cercospora blight and leaf spot (Cercospora kikuchii), and target spot (Corynespora cassiicola). Foliage-applied fungicides are recommended for managing this group of diseases. Fungicides combined with foliar fertilizers have become frequently used in soybean production in NWA. In addition to improving crop nutrition, microelements such as K, Zn, and others, act as elicitors activating plant defense mechanisms, whereas fungicides can prevent or cure fungal infections. Furthermore, biological fertilizers contribute to sustainable production due to their low environmental impact. To evaluate the use of foliage-applied fungicides and fertilizers in the control of late season diseases, field trials were conducted during the 2010-2011 and 2011-2012 growing seasons at Puesto del Medio, Tucumán, Argentina. Treatments were arranged in a randomized complete block design with four replications. Plots consisted of four 6-m rows, spaced 0.5 m apart (12 m2). The same maturity group VIII cultivar was used during both seasons. The following treatments were evaluated: an untreated control, a commercial fungicide (a strobilurin + trizol mixture) applied at R3 growth stage, and three foliar fertilizers (a mixture of cytokinin, gibberellic acid, and indole-3-butyric acid + CaB; potassium phosphite; and zinc phosphite), applied at different moments (R1, R3 or R1+R3) with or without fungicide. Treatments were evaluated in terms of brown spot and Cercospora blight and leaf spot severity. Yield (kg/ha) and seed size (1,000 seed weight) were also determined. In the 2010-2011 growing season, environmental conditions were favorable for both crop growth and disease development. None of the treatments differed significantly from the untreated control in Cercospora blight severity, but most of the treatments with fertilizers and fungicides showed less brown spot severity than the untreated control. No additional benefits in disease control were observed when adding fertilizers to the fungicide. However, the addition of potassium phosphite to the fungicide at R3 increased yield significantly. In the 2011-2012 season, environmental conditions were very unfavorable for crop growth. Three fertilizer treatments decreased Cercospora blight severity significantly, and nearly all of them reduced brown spot severity in comparison with the untreated control, but there were no differences with the treatment that only included the fungicide. Only the fungicide treatment led to significantly higher yields than those of the untreated control.