Pesticides help protect us from diseases carried by insects (like West Nile virus and Lyme disease). Weeds such as poison ivy and poison oak are harmful to people. Other weeds are harmful to livestock. Weeds also attract stinging insects and cause cracking and breaking of concrete, making sidewalks difficult to use and increasing repair costs.
Controlling weeds and insects helps keeps our homes pest-free and our lawns, parks, and other outdoor spaces usable. A recent ban of cosmetic use of pesticides in Canada has led to more expensive road maintenance needs and the degradation of sidewalks and playgrounds as uncontrolled weeds crack and break-up concrete and blacktop. Many weeds also trigger allergic reactions.
In agriculture, pesticides are used to protect crops from damage and diseases. Insects spread diseases and damage fruits and vegetables. When an insect takes a bit out of a plant, the wound is open to infection.
Weeds compete with plants for water, nutrients and sunlight.