Feed supplies for livestock in French Guiana are dependent on grasslands in which weed development can lead to the destruction of forage species. Classical weed control is poorly sustainable. A study of the factors responsible for infestation has shown that it is not the environment that is responsible for the problem, but farmer practices, which affect the forage structure. An explanatory model of pasture invasion dynamics is currently being tested. The degree to which research results have been taken into account by farmers has still to be investigated in the field.