Levels and times of artificial defoliation on performance of second cycle cassava.

Abstract

The information on behavior of crop linked to defoliation is essential to determine the management of herbivore pests. The aim of this study was to evaluate the performance of cassava as a function of the time and level of defoliation applied in the second cycle of cultivation, that is, after the first year of cultivation in which the crop was naturally submitted to the physiological rest period, caused by low temperatures and pluviometric precipitation typical of the southern Brazilian region. We used a randomized block design in factorial 5 x 5.in which 5 levels of defoliation (0, 25, 50, 75 or 100% of defoliation) were applied at 5 different times of 45, 90, 135, 180, or 225 days after sprouting (DAS) of the stems. The following variables were measured: plant height, stem diameter, number of roots per plant, root mass and amount of starch in the roots. The means were submitted to the F test at 5% of probability and analyzed by the regression test using the Sisvar software. Plant height and diameter were inversely proportional to the degree of defoliation when subjected to treatments, especially when subjected to 100% defoliation at 90 DAS. For the root mass, the more drastic defoliation treatments (100 %), when applied at 132 DAS, led to a low production, whereas only the defoliation levels induced a meaningful reduction in the deposition of starch in roots, showing a linear effect and decreasing according to the increase in defoliation. It can be concluded that defoliation between 90 and 135 DAS at the more drastic levels resulted in a greater root mass loss, regardless of the time of defoliation, caused the greatest losses in the amount of starch, therefore, it is recommended to the producer to control this pest before the 90 days of sprouting of the stems at the beginning of the defoliation.