Irrigation and fungicide application on disease occurrence and yield of early and late sown sunflower/Irrigacao e aplicacao de fungicidas na ocorrencia de doencas e na produuvidade do girassol em periodos de safra e safrinha

The objective of this study was to evaluate the effect of irrigation and fungicide application on the occurrence of diseases and cypsela yield of two genotypes of sunflower. The experiments were carried out in Santa Maria-RS, during the regular season in 2007 and the late season, in 2008. Plants were sown on 04/09/2007 and 21/01/2008, in a completely randomized design, with four replicates. A 2 x 6 factorial scheme was used, with the sunflower genotypes Aguara 03 and Helio 358 and six fungicide application schemes, which were determined by the FAST forecasting system, as follows: FAST 16, FAST 22 and FAST 28, without irrigation, FAST 16 IRR under irrigated condition, in addition to irrigated control (CONTROL IRR) and control (CONTROL). Disease progress was analyzed based on weekly observations of the severity of the symptoms. It was verified that irrigation increases sunflower cypsela yield in the regular season, provided that weather conditions are not favorable for the occurrence of alternaria and septoria leaf blights or that fungicides are applied. In the late season, under irrigated condition, fungicide application is necessary to control alternaria and septoria leaf blights. Key words: Helianthus annuus L. Alternaria helianthi Septoria helianthi disease forecast sowing date Objetivou-se, neste trabalho, avaliar o efeito da irrigacao e da aplicacao de fungicidas na ocorrencia de doencas e na produtividade de cipselas de dois genotipos de girassol. Os experimentos foram conduzidos em Santa Maria, RS, nos periodos de safra de 2007 e safrinha de 2008. As semeaduras foram realizadas em 04/09/2007 e 21/01/2008, sendo utilizado o delineamento inteiramente casualizado, com quatro repeticoes. Foi utilizado um esquema fatorial 2 x 6, constituido pelos genotipos de girassol Aguara 03 e Helio 358 e seis esquemas de aplicacao de fungicida, determinados em funcao do sistema de previsao FAST, os quais foram: FAST 16, FAST 22 e FAST 28, sem irrigacao, FAST 16 IRR, em condicao irrigada, alem das testemunhas irrigada (TEST IRR) e nao irrigada (TEST). O progresso da doenca foi analisado com base nas observacoes semanais da severidade dos sintomas da doenca. Verificou-se que a irrigacao aumenta a produtividade de cipselas de girassol no cultivo de safra desde que as condicoes meteorologicas nao sejam favoraveis para a ocorrencia de mancha de alternaria e septoria ou que se apliquem fungicidas. Na safrinha em condicao irrigada, a aplicacao de fungicidas e necessaria para