Grouped by How or When They Work 

Pesticides can also be classified according to how or when they work. Some groups that describe how or when pesticides work are:

  • Contact pesticides generally control a pest as a result of direct contact. Insects are killed when sprayed directly or when they crawl across surfaces treated with a residual contact insecticide. Weed foliage is killed when enough surface area is covered with a contact herbicide.


  • Systemic pesticides are pesticides which are absorbed by plants or animals and move to untreated tissues. Systemic or translocated herbicides move within the plant to untreated areas of leaves, stems or roots. They may kill weeds with only partial spray coverage. Systemic insecticides or fungicides move throughout treated plants and kill certain insects or fungi. Some systemic insecticides are applied to animals and move through the animal to control pests such as warble grubs, lice, or fleas. Some pesticides only move in one direction within the plant, either up or down. Knowing what direction the pesticide moves will help guide your decisions. For example some insecticides only move upwards in plants. If applied to the root zone, it will travel throughout the plant, but if applied to the leaves it will not move throughout the plant. Some pesticides are considered locally systemic. These will only move a short distance in a plant from the point of contact.