What factors could cause dandelions and clovers to grow in a garden sprayed with

[SmileyFace]

pesticide? Don't need a detailed answer. Just list some points if there are any. Thanks.
I meant herbicides...

[pissy_old_lady]

adjoining land with weeds
pesticide for other specific plants
sprayed incorrectly (in the rain)
needs continuing maintenance (over due)

[Lar]

depends on the pesticide used... insecticides kill insects..herbicides kill vegetation both are pesticides. If you sprayed for insects the weeds would not be effected...if you mean you used an herbicide and the weeds came up, you probably used a grass killer and these two weds are broad leafed weeds.