Degradation generally refers to weed infestation, which in turn can be facilitated by pests or deteriorating soil conditions. The proliferation of weeds can be a symptom of soil exhaustion or compaction, but not always. Pastures with numerous termite mounds appear to be in poor condition. The infestation of volunteer plants can thus be a consequence of soil depletion and compaction, overgrazing, underutilization, or insufficient weeding. Weed infestation is a sure sign of poor pasture management.
Weeds originate from seeds dropped by birds, other animals, and the wind, and from imported seed.
Stump resprouting in relatively new pastures can also quickly shade out grass. Weeds can take over relatively fertile pasture if they are not checked. Overstocking or understocking can also favour the emergence of unwanted plants in pastures. Dozens of unwanted plants arise in pastures in Amazonia. The composition of weedy communities varies markedly within an area and between different parts of the Amazon.