Understanding Herbicide Types
Pre-Emergent and Post-Emergent Herbicides
There are two different types of herbicide... pre-emergent and post-emergent. Like their names infer, pre-emergent herbicides kill the plant before it emerges and post-ermergent herbicides kill the plant after it has already emerged.Table of Contents
- Pre-Emergent Herbicide
- Post-Emergent Herbicide
- Dual Pre-Emergent and Post-Emergent Herbicide
A pre-emergent herbicide is meant to be a preventative treatment for weeds, stopping them before they emerge. They create a barrier in the top couple inches of soil, preventing and killing them weeds from growing above the soil as they germinate.
Pre-Emergents and Grass Seeding
Pre-emergent herbicides are non-selective when it comes to what seeds they prevent from germinating, with the exception of a few unique cases such as Tenacity. Therefore, follow the label rate to determine how long you want pre-emergent protection and make sure that you are past that protection time-window when seeding.
Ex. If you use pre-emergent at the 4 month rate, you must wait 4 months after applying to put down grass seed.
The above is the seeding time-window table for Barricade DG Pro.
A post-emergent herbicide is used to kill weeds after they have already emerged. This can be done via either a broadcast (granular) or blanket (liquid) application, if the weeds in the lawn are dense enough, or on a one-by-one basis via spot spraying. Post-emergent herbicides are mixed with a surfactant in order to increase their efficacy.
Surfactant is mixed with liquid herbicides when doing post-emergent applications to increase their efficacy. They break the surface-tension of the liquid on the plant in order to have an even-coating on the leaf tissue, rather than have the liquid bead up and slide off of the surface. It makes the liquid apply more like a paint than water.
Surfactants are not used with pre-emergent applications, as the pre-emergent application is meant to go down to the soil level. In that case, you want the liquid to bead up and slide off of the plant to the soil. That is also why pre-emergent’s typically need to be watered in so they get washed off the plant and go down to the soil level.
Dual Pre-Emergent and Post-Emergent Herbicide
There are some products, such as Tenacity, which have both pre-emergent and post-emergent properties.