In the present study, under controlled conditions, the influence of temperature (10, 15, 20, 25 and 30°C) and leaf wetness duration (6, 12, 24 and 48 hours) was studied on the severity of Alternaria leaf blight of carrot caused by Alternaria dauci. The relative density of lesions was influenced by temperature and leaf wetness duration (P<0.05). The disease was more severe at the temperature of 25°C. Data underwent non-linear regression analysis. The generalized beta function was used for fitting the data on disease severity and temperature, while a logistic function was chosen to represent the effect of leaf wetness duration on the severity of leaf blight. The response surface resulting of the product of the two functions was expressed as ES = 0.004993 * (((x-8)1.13125) * ((36-x)0.53212)) * (0.39219/(1+25.93072 * exp (-0.16704*y))), where: ES represents the estimated severity value (0.1); x, temperature (ºC) and y, leaf wetness duration (hours). This model must be validated under field conditions to be used as a forecasting model for Alternaria leaf blight of carrot.
O gorgulho aquático, Oryzophagus oryzae (Costa Lima), é praga importante nas lavouras de arroz irrigado. Suas larvas, conhecidas por bicheira-da-raiz, danificam o sistema radicular das plantas. A prática do controle biológico desse inseto precisa ser aprimorada. Assim, foi conduzida uma pesquisa objetivando verificar as taxas de mortalidade de O. oryzae, infectados por Beauveria bassiana (Bals.) Vuill. em armadilhas luminosas, instaladas em lavoura de arroz irrigado. Duas armadilhas receberam aparato de contaminação fúngica, com massa de B. bassiana, preparada em arroz autoclavado. Uma terceira armadilha ficou isenta, como testemunha. Insetos capturados de outubro de 2013 a março de 2014 foram mantidos em laboratório para a verificação de mortalidade e infecção fúngica, caracterizada pelo crescimento micelial nas articulações. A mortalidade dos indivíduos artificialmente contaminados foi de 73,1%, enquanto que na testemunha foi de 0,8% (infecção natural). Armadilhas luminosas com aparato de contaminação fúngica foram eficazes no controle biológico de adultos de O. oryzae.
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