Mode of action- The way a pesticide acts on a pest. often group pesticides into classes based on their mode of action 

Residual insecticides provide control for hours, days, weeks, or even longer after application. They are desirable when a pest poses a constant threat, yet the pesticide will present little risk to people or the environment. 

Nonresidual insecticides are effective only at the time of application or for a short time afterward. They are effective only if the pest is active in the treatment area at the time of application. useful in situations where the pest is unlikely to return or where people and pets might be exposed. 

Contact insecticide kills insects that come into contact with it. This might be when an insecticide is sprayed directly on insects or when insects walk on a surface ( e.g., leaf, house foundation) that has been treated with a residual insecticide. 

Stomach poison is effective only if an insect swallows it, as when an insect feeds on a treated plant or eats poisoned bait. 

Systemic insecticide is a special kind of stomach poison that is absorbed by and spreads throughout a treated plant or animal; an insect is killed when it feeds on any part of the plant or animal. 

Contact herbicide kills plant tissue in the immediate vicinity of where it was absorbed into the top growth to which it is applied; it controls annual and biennial weeds and any type of weed seedling. 

Systemic herbicide will kill established perennials because it is absorbed at the point of contact and then moves throughout the entire plant so that it reaches and kills the underground structures.