Problems Associated with Pest ControlThe two main types of pest control are biological control and chemical control, and there are different types, each of which is associated with problems. Chemical pesticides can be divided into three categories: insecticides, herbicides and fungicides. Each of them fights different types of pests: insects, weeds and pathogenic fungi. There are three types of pesticides that work in different ways to eliminate pests and increase crop yield. Contact pesticides are sprayed directly on crops. They are absorbed by insects through stigmas, which are gas exchange pores, and are absorbed by weeds and fungi through their surfaces. The pests are poisoned and therefore cannot compete with or destroy cultivated plants. Contact pesticides are relatively inexpensive, but their effects are short-lived and they must be applied regularly. This method is not completely effective; However, because spraying crops does not guarantee that every pest is poisoned and killed, plants may still be destroyed. Systemic pesticides are also sprayed on crops, but act differently to come into contact with the pesticides. They are absorbed by the crop and transported around the plant. Sap-sucking insects such as aphids will feed on the plant, absorb the pesticide and be killed. Weeds will also absorb the pesticide and it will kill all of its plant tissues, including underground roots. This type of pest control is very effective because it is not necessary to spray every insect, and it is also selective, so the cultivated plant will not be damaged nor will other insects that pose no threat. Residual pesticides are sprayed on the ground or soil. collect the seeds before planting them. They remain active in the soil by killing fungal pores, insect eggs and larvae, and weed seedlings. These are effective in the sense that many pests do not become a problem, but once the plant has grown, any insect eggs laid on the plant will not necessarily be killed unless the plants are sprayed with another guy.