Effects on plant density and seeds production of Centaurea spp. after herbicide application

BECKER GUILLERMO; FRANZESE JORGELINA; GONZALEZ SOFÍA

Rosario

Congreso; IX International Rangeland Congress; 2011

Introduction Centaurea spp. are annual exotic herbs that invade disturbed sites (eg. road berms, removed soil, etc). These plants are scarcely consumed by wild or domestic animals, and they strongly compete with valuable grassland species. Although these species have a low total cover (2-3 %) in our study site, they are mainly established in sectors of high productive potential (i.e. valleys), causing a resource limitation for livestock grazing. Centaurea spp. produce abundant seeds that germinate in early autumn, and the plants form rosettes that flower in spring. The aim of this work was to study the effect of herbicides on Centaurea spp. density and seed production. Material and Methods We studied the effects of a herbicide combination (180 cc/ha of piclorán + 8 g/ha of metsulfuron + 50 cc of helping) on the number of seed heads/plant (n=20), seeds/seed head (n=20) and density of Centaurea plants. The study was carried out at a ranch in Collon Cura in Neuquén Province, Argentina (40º 05´-40º 20´ S; 70º 40´-70º 30´ W). Herbicide applications were both aerial and terrestrial (H). Non-treated sectors were used as Control (C, n=10). In March 2010, we cut all plants within 0.2 m2 sectors in each site. The samples were processed in laboratory. We collected seeds and we determined their weight (n=1000) and germination percentage. T test or Mann-Whitney were used to compare data. Results Density (plants/m²) was similar in both treatments (27.6 in H and 25.8 in C, p> 0.05). Nevertheless, the seed heads/m², and the seeds/m² were 130% and 147% lower in H than in C (p <0.05). Seeds/seed head, 1000 seeds weight and germination were similar in both treatments (p> 0.05; Table 1). Conclusions Herbicides affected negatively the seeds production of Centaurea., mainly due to the reduction in the seed heads number/plant. Nevertheless, the quality of the seeds (weight and germination power) and plant density was not affected, for which we conclude that Centaurea maintains a high potential for invasion in the field.