Condições para ocorrência da seca dos ponteiros laterais em clone de Eucalyptus urophylla x E. grandis

Abstract

The Dried out of Side Tips (DST) in Eucalyptus (Pseudoplagiostoma eucalypti Cheew., M.J. Wingf. & Crous) is a disease that affects the productivity of forest plantations in Brazil. Due to little knowledge about the epidemic, the study deepens, in two chapters, the understanding of the disease in relation to the environmental conditions of the affected areas. In the first article, it was evaluated, for the period of three and a half years, as conditions of humidity, temperature and exclusion, as well as the severity of the disease, in such a way as to age and periods with greater intensity of DST. The experiment was performed in areas undergoing disease outbreaks, where the clone of E. grandis x E. urophylla had been planted, with 3 x 2-meter spacing. The experimental outline had 12 treatments, regarding the eucalyptus resprouting ages, which allowed analyzing the occurrence of DST for different ages and times of the year. The severity of the disease was calculated as from the weighted mean and the monthly in-field assessments, varying from zero to three (minimum and maximum disease infection). The values of severity were used for calculating the disease growth rate. The meteorological data were organized into graphs and the monthly rainfall values compared by the Mann-Kendall (statistical) test. The test showed there was a significant upward trend of rainfall from the first to the second year and from the latter to the third year. The curve of the progress of the disease also shows the difference among the years assessed, besides showing that the disease manifests with greater severity from the third to the sixth month of age, June-October being the months with the greatest incidence of DST. Therefore, the recommendation is to test planting clones susceptible to the disease in October and/or November as a strategy for obtaining plants with a smaller incidence of DST, since larger-sized plants would be able to bear the pathogen in the critical months. In the second article, this study aimed to evaluate the severity of the disease and the environmental conditions that affect it. Thus, from the environmental data of four weather stations, the following conditions were verified concomitantly: relative humidity above 85%, maximum temperature below 28ºC, rainfall in the range of 1-10 mm and leaf wetting time at 24 h, indicating favorable times (June to October), unfavorable (January to March), and transitory (April, November and December) to the disease. In humid months and when the temperature is not limiting, the occurrence of one or more days with all the variables favorable to the pathogen intensifies the disease. The temperature above 28º C, from October, is one of the reasons that makes the severity of the disease reduce in November and return in June. The map generated based on the severity and environmental conditions reveals greater disease risk in the following areas: Barcelona and Taquari, BA and smaller in Pedro Canário, ES.