All pre emergent herbicides have to be applied before the weeds come up. Look at it this way, suppose you are washing dishes. Do you squirt soap in the sink before you fill it with water or do you squirt soap in the water before you start washing dishes or do you squirt soap on the sponge? It doesn't really matter a whole lot, you just have to use the soap when you're washing them, but soap is no help when you rinse them.

@@carlherrnstein9544 thanks it is just the incorporation part I have problems with so the chemical doesnt get the seed your growing

@@tomnapier681 It depends on the crop you are planting and the herbicide you use. I'v only used pendimethaln as a pre emergent herbicide, prowl is a common brand but there are other generic brands. Pendimethaln is a selective herbicide, Google search "prowl h2o herbicide label" you can read the entire list of crops that prowl is labeled for and the weeds it controls. Keep in mind that there are many different brands of pendimethaln that are basically generic brands and work exactly the same. There are also many other chemicals that are pre emergent herbicides an they come in different forms (granules that are broadcast(treflan and preen), liquids that are sprayed(pendimethaln)

@@tomnapier681 They are selective herbicides that generally don't injury your crops. You have to choose the herbicide based on the crop you have planted. Pendimethaln is very effective an safe for the environment, but kills some crops like pumpkins. Treflan works well if it is incorporated in the surface of the ground(it's a granule) if it's not worked in it doesn't work. Preen is another granule pre emergent herbicide. Often it's necessary to apply a pre emergent and a post emergent herbicide to clean up what the pre emergent didn't prevent, sometimes mechanical cultivation is still needed. Read the label of any herbicide you use.

@@carlherrnstein9544 seems different countries have different chemicals never seen granular treflan only liquid to spray on and incorporate Never heard of Preen here its a washing product