Pesticides and fertilizers can be placed into two categories:  Soil activated and foliar activated (or a combination of both)

Soil Activated
The active ingredient or nutrient works best if applied to the soil.  In many cases, avoiding contact with the plant is highly advantageous.  There has been much research completed about the advantages of targeting the soil surface for products like pre emergent herbicides.

Foliar Activated
The active ingredient or nutrient works best if applied to the plant itself.  These are active ingredients or nutrients that the target is to absorb the chemistry into the plant for maximum effectiveness.  An example of this weed killers that are transported within a plant for maximum effectiveness.  Liquids are typically very effective with these applications, although granule technology is making significant progress.

Future Contact: 

The residual activity of liquids and Granules have their respective advantages and limitations in terms of control beyond the 24 to 48 hours application.

In addition to providing initial control of leaf and stem pests, liquids have residues that remain in the thatch providing control of which inhabitants for some time.  The length of this residual activity is, however, generally shorter than that of granules.  The reasons for the longer residual with granules are:  they are protected from light which may break down the insecticide leaches off granules over a period of time which usually exceeds the length of residual activity from liquids.

Irrigation – Rain:
Control materials vary widely in water solubility and capacity for adsorption to organic matter.  Water, as rain or irrigation, does not completely circumvent adsorption, but it does accomplish as much movement in the target zone as possible.

“Generally, granular materials should be applied when grass blades are dry so the particles bounce off the grass blades and sift deeply into the turf.  While the urgency to irrigate is not as immediate as for liquid materials, it should be done as soon as possible”.

Reference these excerpts from:
“Destructive Turf Insects, second edition” by Dr. Harry D. Niemczyk and Dr. David J. Shetler