Afídeos vetores de vírus em trigo e cevada em Guarapuava - PR: monitoramento, manejo de inseticidas e análise econômica associada ao controle químico

Abstract

Understanding the behavior of aphid pest in winter cereals is an important strategy associated with the insecticide management. The aim of this study was to evaluate the key aphid species and their parasitoids in barley and wheat, and to evaluate the agronomic and economic efficiency of the different insecticide uses to control aphids. The aphid and parasitoids monitoring and the evaluation of the use of insecticides were conducted in Guarapuava-PR during the winter seasion in 2011 and 2012. Aphids were weekly sampled with yellow trays, and they were counted and classified to the species level. Curves were fitted with the total aphids (aphids/tray/week), and these were compared with climate variables during the collection period. Mummified aphids were collected, and after emergence, the parasitoids were identified at genus or species level. The experimental design to evaluate the protective effect of different insecticide management strategies was a completely randomized block design in a split plot arrangement with four replications. The main plots received insecticide managements (T1: seed treatment (ST) + insecticide applied in shoot at 15 days interval; T2: just ST; T3: insecticide applied in the shoot, when the population reached the control level (CL); and T4: no insecticide), and in the subplot different cultivars of barley and wheat. In the 2012, it was included one more treatment in the main plot (T5: TS + insecticide applied in shoot when it reached the CL) and in the subplot (one more cultivar of barley and wheat). Aphid species sampled in both years were: Rhopalosiphum padi (81.3%) Metopolophium dirhodum (12.2%), Sitobion avenae (4.2%), Rhopalosiphum maidis (1.0%), Sipha flava (0.9%), Schizaphis graminum (0.3%) and Sipha maydis (0.2%). The parasitoids collected were: Diaeretiella rapae, Aphelinus spp. Aphidius spp. and Lysiphlebus testaceipes. There were differences in the management of insecticides for disease index in both years, while the yield damage and other variables was influenced by year and aphid population. Significant economic differences between treatments were also observed. It was concluded that the ST with insecticide is an excellent tool for controlling aphids in years with low aphid population pressure, while in years with high populations, the application of insecticide in the shoot is also necessary.