Plants produce large quantities of seeds, about the size of ground pepper, that are dispersed by wind, flowing water or by adhering to the fur, feathers, or feet of wetland mammals and birds. Many exotic weeds and insects have been brought under control using the approach of biological control. This works by reuniting a pestwhether weed or insect pestwith its ancestral natural enemies. Weed biological control projects have used 350-plus species of insects and pathogens against 133 plant species around the world, with numerous permanent successes. Usually, biological control represents the last, best hope for fighting many of the worst invaders.
Purple loosestrife is a prime example.
Vast stands of loosestrife defy most control efforts. Hand picking works only in the smallest stands when the plant first arrives. In a few cases flooding may kill loosestrife, but many of the worst infestations are in standing water. In addition, flooding can kill already threatened native plants. Burning simply annoys the plant.