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How Does a Pre-Emergent Actually Work?

When it comes to weed control there two types of products: pre-emergents and post-emergents. Pre-emergents affect weeds before they emerge from the seed, while post-emergents affect weeds that have already emerged from the soil. Both are used in lawn care, as there is no one solution to eliminate all weeds. In another article, you can learn more about post-emergents. In this article, you will learn how pre-emergents work.

Two of the pre-emergents Weed Xtinguishers utilizes for your turf grass applications belong to the triazine and alkalyzine herbicide groups of Group 5 and Group 29 herbicides, respectively. There are multiple herbicide categories, and we use these two specific herbicides for different reasons that we will go into further. What is important to know is that both pre-emergents target a specific function of the plant rendering it inactive.

Group 5 herbicides have a mechanism that singles out the D-1 protein of the photosystem II in chloroplast thylakoid membranes. The pre-emergent molecule binds to the QB-binding niche preventing the plant’s ability to transfer electrons from the QA which is normally the function of the D-1 protein. This electron transfer is essential in the production of the sugary energy molecule that plants create from photosynthesis known as ATP, or adenosine triphosphate. Chloroplast thylakoid membranes are where plants create energy from sunlight. Essentially, Group 5 herbicides create a build-up of sunlight energy in the chlorophyll by removing the ability to transfer this energy into a sugar causing free radical ions to wreak havoc on chlorophyll and cell walls.

Chloroplast II

On the other hand, there is the Group 29 pre-emergent that can be used. This chemical attacks a separate ability of the plant, its ability to create new cells, also known as a cellulose inhibitor. There are two different ways to inhibit cellulose production in plant cells. The first prevents the ability to make cellulose completely while the other prevents cellulose from creating cell walls. Without cellulose, a plant cannot make rigid cell walls allowing for growth. Cellulose is to plants what bones are to humans. Alkalyzine chemicals work by inhibiting all biosynthesis of cellulose. This is done by targeting the Cellulose Synthaze A proteins (CESA) and slowing the rate of microtubule colocalization of this protein to a near standstill. This means any seeds in the soil are incapable of creating new growth cells.

Thankfully, the two aforementioned pre-emergents were designed for use in warm season turf grasses. This means at the standard applicable mix rate these chemicals will target certain plants and keep your turf grasses safe and healthy.

The molecules of the pre-emergent organically bind themselves to the particles of soil prohibiting germination of seeds or their ability to grow. This is done by a particular mechanism of action dependent on the formulation of the chemical being used. According to WSSA, the Weed Science Society of America, there are 30 different classifications of mechanisms of action in herbicides available to the United States. Twenty-nine of them are attached to a particular mechanism of action and the thirtieth is for those that are not classified. If you would like to see all of the mechanisms of action, please follow this link:

The science behind pre-emergents has truly revolutionized lawn care. Whether it’s inhibiting photosynthesis or preventing the generation of new cells, they work below the surface to make sure that weeds never see the light of day. Pre-emergents are the unsung heroes in weed control.

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