ABSTRACT
The expansion of crops and improved pastures into eastern Colombia’s well-drained, lowland savannas has been limited by edaphic and biotic factors. Most soils in this area have excellent physical characteristics but poor chemical properties, i.e., low pH (4 to 5), available phosphorous, organic matter content, and cation exchange capacity due to about 80% aluminum saturation (Cochrane et al. 1985). A major initiative of the Centro Internacional de Agricultura Tropical (CIAT) in conjunction with the Instituto Colombiano Agropecuario (ICA) has been to develop drought-resistant, high yielding grass and legume forages selected for these soil conditions. Brachiaria decumbens Staph cv. Basilisk is the most widely planted pasture grass on the Colombian savanna. This grass’ high susceptibility to spittlebugs (Homoptera; Cercopidae) has resulted in the importation of more tolerant species such as B. humidicola (Rendle) Schweick. In addition, the grass Andropogon gayanus Kunth was released in Colombia as cultivar “Carimagua 1” (1980) and is being widely adopted by ranchers. A. gayanus grows well in poor soils and resists spittlebugs (Ferrufino and Lapointe 1989). These three species are the major forage grasses introduced to the Colombian savanna. A. gayanus has been particularly successful when associated with the legume Stylosanthes capitata Vog. cv. Capica, released in 1983. Since commercialization, the only major arthropod pests of A. gayanus have been leaf-cutting ants. A. gayanus is particularly susceptible to ant predation when first established, due to its small seed size. Regrowth does not occur if leaf-cutting ants harvest the germinating plants, resulting in poor, patchy establishment with subsequent weediness.
