Uso de fosfito de potássio combinado com fungicida no controle da ferrugem da folha do trigo

Abstract

There are numerous diseases that attack the wheat crop, leaf rust caused by the fungus Puccinia triticina Eriks, one of the most common among them, and is present in almost all the regions producing the cereal in the country. One of the alternatives for the control of plant diseases is the use of potassium phosphite. Studies have shown that the single application or in combination with fungicide can reduce the severity and incidence of diseases caused by fungi in cultivated plants. Thus, this work had the objective of evaluating the effect of potassium phosphite combined with fungicide in the control of wheat leaf rust. The experiment was carried out in the experimental area of the Federal University of Pampa - Campus Itaqui, following the randomized block design, with five treatments and four replications. For the execution of this work was used the cultivar of wheat JADEÍTE 11, cultivar moderately resistant to the rust of the wheat leaf. The treatments consisted of Yantra® (Potassium Phosphite 0.6 l ha-¹) and Nativo® (Trifloxystrobin Tebuconazole 0.6 l ha-¹) and control, T1-control (no application), T2-two fungicide applications, T3 - two applications of phosphite, T4 - one application of fungicide and one application of phosphite and T5 - one application of phosphite and one application of fungicide. Two applications were made, the first at the flowering stage (65 days after sowing) and the second at 15 days after the first application. The evaluations began shortly after the first application, and occurred weekly evaluating the severity of the disease in ten whole plants and ten leaves flags per plot. For the evaluation of severity, the diagrammatic scale of COBB modified by Barcelos (1892) for wheat rust was used. From the severity data the area under the disease progress curve (AACPD) was determined. The data were submitted to analysis of variance by the F test and the means grouped by the Scott & Knott test at 5% probability using the Sisvar Statistical Program. The treatments T2 (Fungicide + Fungicide) followed by treatment T4 (Fungicide + Phosphite) showed the lowest severity of wheat leaf rust, with reductions of 27.78% and 15.42%, respectively, in relation to T1 (control without application). Regarding the productivity parameters, the treatments T2 and T4 also presented the highest values of productivity, hectoliter weight, thousand grain weight and number of grains per spike. The increase in productivity was 54.88% for the T2 treatment and 50.52% for the T4 in relation to the control. According to the results obtained, we can observe that the order of application of the products will influence the severity of the disease and in crop productivity. Although T4 (F + FOS), when compared to T2 (F + F), showed less efficiency in the control of leaf rust severity, in the productivity variables there was no statistical difference between the treatments. Therefore, when applied after the fungicide, potassium phosphite reduces the severity of leaf rust and maintains productivity levels. This allows the replacement of a second fungicide application with a potassium phosphite application.