Control of native undesirable species from Rio Grande do Sul natural pastures

Abstract

The preservation of natural pastures is important to Rio Grande do Sul because, in addition to its economic value, it has ecological implications. Inadequate or poor management of native pasture can cause an increase in frequency of undesirable native species. Undesirable species can decrease production from pastures, through competition with desirable forage species, or by directly affecting livestock production through reduced intake, or even through toxic effects. Undesirable species, from the animal production point of view, most frequently found in Rio Grande do Sul, are caraguatá (Eryngium horridum Malme), carque- ja (Baccharis trimera Less.), chirca (Eupatorium buniifolium Hook.), mio-mio (Baccharis coridifolia DC.) and alecrim (Vernonia nudiflora Less.). Some strategies to control these species include mechanical control, by mowing or dragging iron shanks; chemi- cal control, by herbicides; biological control, by grazing, as well as other management strategies (e.g., fertilization) that could favor native pasture in intraspecific competition. Some of these interventions influence vegetation dynamics, such as grazing and burning. Obviously, the efficacy of all these methods depends on morphological and phenological characteristics, which vary among species. Therefore, it is important to implement the management strategy during the right utilization period. Experiences show that interaction between methods can promote greater efficiency upon species control. The aim of this review is to aggregate the information about undesirable native plants in Rio Grande do Sul and methods for their control.