Response of Eucalyptus (Eucalyptus urograndis) Plants at Different Doses of Glyphosate

The aim of this study was to evaluate the response of eucalyptus plants submitted to the application of glyphosate increasing rates. The doses 0.0, 3.6, 7.2, 18, 36, 72 and 180 g ha-1 of acid equivalent (ae) of glyphosate were applied on plants. At 7, 15, 22, 29, 36 and 42 days after application (DAA) was determined leaves relative chlorophyll content and quantum efficiency of photosystem II. At 22 and 42 DAA plant height and stem diameter were measured. At 42 DAA were determined the leaves dry mass, stem dry mass and foliar area. The height, diameter, leaves and stem dry masses and foliar area were converted to percentages, whereas the controls as 100%. These variables were fitted to the model described by Gauss equation. The data chlorophyll content and quantum efficiency of photosystem II were submitted to mean comparison, and when they differed, we performed the Tukey test at 5% probability. All the features presented here showed some hormetic effect promoted by reduced rates of glyphosate and the increments observed in these characteristics (when compared to control) ranged between 5.92 and 33.18% at 42 DAA. From average curve with height, diameter, leaves dry mass, stem dry mass and foliar area can be concluded that the increase averaged 12% on application of 16 g a.e. of glyphosate ha-1. For leaves chlorophyll content significant differences were observed only at 29 DAA, while for quantum efficiency of photosystem II significant differences were found only at 7 DAA.