Pest Control Prevent: -damage to food and animals -spread of diseases How? -using poisonous chemicals How? -insecticides -herbicides		Large pest populations are a major concern to humans because of their negative effects. Therefore humans try to control and even eliminate pest populations. Large animal pests such as deer and pigeons are usually not difficult to control. They can often be stopped by fences or simply frightened away. Because insect pests are so small and numerous, they are more difficult to control. Poisonous chemicals, called insecticides, are often used to kill unwanted insects. Similar poisons, called herbicides, are used to control difficult plant pests.