Pre-emergence herbicides are another tool to improve weed control over mulch alone. Most pre-emergence herbicides do not control existing weeds. Therefore, the application timing is essential in ensuring that the herbicide is in place before weed germination. Late winter or early spring applications control summer-annual weeds such as large crabgrass and prostrate spurge.
» First and foremost, they give you a much needed “head-start” on keeping the weeds under control. Just about the time it gets too hot for most people, and the thought of spending hours and hours in the garden, most weeds are just hitting the peak of their growing season.
» Weeds you pre-emergently control do not have the opportunity to produce seed. Therefore, if you apply pre-emergents annually, the weed population will decrease with each passing year.
» Pre-emergence herbicides usually last a few months. Most post-emergence herbicides do not have a residual effect, which means they do not control weed germination after the application. This will result in more frequent herbicide applications if you rely solely on post-emergence control.
» When they are applied correctly and in accordance with the label, pre-emergence herbicides pose less risk of “non-target” plant damage than post-emergence herbicides.
» Pre-emergence herbicides often are available in granular form, which reduce the risk of drift spray.
» Pre-emergents control weeds during germination, so no unsightly dead foliage appears after the weeds die.