Over-application of pesticides may result in the accumulation of residues in the soil. These residues may be directly toxic to grass growth. Over-application of pesticides will often result in pest resistance to the applied chemical. Naturally occurring mutations may create super insects or weeds that will be almost impossible for you to control with pesticides in the future. Pest Management Many pests attack lawns.
Weeds are simply plants growing in the wrong place.
In the case of your lawn a weed is any plant that is not the variety of grass that was originally seeded to produce your lawn. There are over 30 weeds common to lawns in the Pacific Northwest. Most of these weeds can be easily eliminated from your lawn. Besides using pesticides, there are management options that discourage competition from weeds. Chemicals applied to lawns that kill weeds are called herbicides.