Fontes de fosfito e acibenzolar-S-metílico associados a fungicidas para o controle de doen as foliares na cultura da soja Phosphite sources and acibenzolar-S-methyl associated to fungicides on the control of foliar diseases in soybean

O objetivo deste trabalho foi estudar diferentes fontes comerciais de fosfito e acibenzolar-S-metílico (ASM) seguidos de uma aplica o de fungicida no controle do míldio, do oídio e da ferrugem asiática, para reduzir o número de aplica es de fungicidas e aumentar o espectro de controle das doen as da soja. Foram conduzidos dois experimentos na regi o de Ponta Grossa, PR, nas safras 2006/07 e 2007/08. O delineamento experimental utilizado foi de blocos casualizados com quatro repeti es. Os tratamentos foram cinco fontes comerciais de fosfitos de potássio e uma de manganês (450 g P2O5 ha-1) e ASM (12,5 g i.a. ha-1), aplicados nos estádios V7 e R2. Os tratamentos com fosfito e ASM receberam uma aplica o do fungicida piraclostrobina + epoxiconazole (66,5 + 25 g i.a. ha-1) no estádio R3 e foram comparados com uma em R2 e duas aplica es do mesmo fungicida, aplicados em R2 e R5.1, e a testemunha. O uso de fosfito e ASM reduziram significativamente a área abaixo da curva de progresso do míldio e n o tiveram efeito sobre o oídio e a ferrugem asiática. O maior número de aplica es do fungicida aumentou o controle dos patógenos biotróficos sob maior press o das doen as. The goal of this study was to evaluate commercial sources of phosphite and acibenzolar-S-methyl (ASM) followed by one fungicide application on the control of downy mildew, powdery mildew and asian soybean rust, reducing the number of fungicide applications and increasing the control spectrum of these soybean diseases. Two field experiments were carried out in Ponta Grossa, Paraná state, Brazil, during the 2006/07 and 2007/08 growing seasons. The experimental design was of randomized blocks with four replications. Treatments consisted on five sources of potassium phosphite and one of manganese (450 g P2O5 ha-1) and ASM (12.5 g a.i. ha-1) sprayed at the V7 and R2 stages. Phosphite- and ASM-treated plants received one application of the fungicide piraclostrobine + epoxiconazol (66.5 + 25 g i.a. ha-1) at the R3 stage and were compared to plants which received two fungicide applications at the R2 and R5.1 stages, as well as to untreated plants. The use of phosphite and ASM significantly reduced the AUDPC for downy mildew. No effects were observed for powdery mildew and Asian rust. The higher number of fungicide application increased the control of biotrophic fungi under higher disease pressure.