Short- and long-term effects of weed control on pastures infested with Pteridium arachnoideum and an attempt to regenerate abandoned pastures in South Ecuador

Pteridium spp. (bracken) is one of the most persistent weeds worldwide. This communication reports for the first time, experiments to control the aggressive neotropical fern, Pteridium arachnoideum. In South Ecuador, where former pastures are overgrown by P. arachnoideum, 13 different control measures were repeated six times over a time period of 23 months: cutting of the fronds, various herbicides, covering with plastic sheeting and alternating combinations thereof. Subsequently, the pasture grass Setaria sphacelata was planted. Growth of P. arachnoideum and later the grass was monitored monthly using the variables cover and height of vegetation. Pteridium arachnoideum frond biomass was determined at the end of the treatments. None of the treatments resulted in a complete eradication of the weed. The efficacy of the treatments differed considerably, but the subsequently planted grass balanced out these differences, suppressing the fern to a cover of <40%. Thus, in spite of the high resistance of P. arachnoideum to any kind of control, regeneration of abandoned pastures is possible, using a two-step strategy: (i) depleting the reserves in the rhizomes by repeated killing of the leaves and (ii) subsequent suppression by a highly competitive pasture grass. For practical weed management, three consecutive treatments with the herbicide mixture of picloram and metsulfuron methyl, or four consecutive cuts of the fronds, are recommended at intervals of four months to achieve maximum control.