Preemergent herbicides are a type of herbicide that is applied to soil before weeds have a chance to germinate. These herbicides work by forming a barrier in the soil that prevents weed seeds from sprouting and growing.
The active ingredient in preemergent herbicides typically targets enzymes that are essential for plant growth. When a weed seed attempts to germinate and grow, it takes up the herbicide from the soil, which then interferes with the plant’s ability to produce necessary proteins and enzymes for growth. This causes the weed seed to die before it can emerge from the soil and establish itself.
Preemergent herbicides are particularly effective against annual weeds, which complete their life cycle within a single growing season and rely on seeds to reproduce. By preventing these weeds from germinating, preemergent herbicides can significantly reduce the number of weeds that appear in each area.
It is important to note that preemergent herbicides must be applied before weed seeds have a chance to germinate, which typically means they are applied in early spring before soil temperatures rise and trigger seed germination. Preemergent herbicides have residual effects that last for several weeks to several months in the soil. The goal of the residual is to create a barrier that extends through the germination season of a particular target weed. The most common use of preemergent herbicide is to prevent summer crab grass. This weed germinates in April and begin to appear above ground May-September. Timing the application of a preemergent before germination which also resides in the soil through August is important to maintaining a crabgrass free lawn.
The fallacy of preemergent is that they prevent all weeds from germinating. Depending on the type of grass you have, professionals have 3-4 product options to choose from. Each product has a similar list of weeds they prevent, with a few caveats, but some weeds can overcome this protection and germinate despite a properly applied preemergent barrier.
Fescue lawns become challenging as the preemergent barrier needs to be worn off prior to aerating and overseeding the lawn. This leaves the lawn susceptible to weed invasion in the fall. In the fall, Poa Annua germinates in all grass types and begins to show up in late winter and early spring. Given this cycle, it has become one of the more difficult weeds to prevent. Even though preemergent herbicide can target this weed, the timing of the application is required in the fall, which eliminates the homeowner’s opportunity to perform an important aeration and overseeding.
Although they are not perfect, preemergent herbicide is an effective preventative solution to weed control. Used appropriately in concert with post emergent herbicides, lawns can be maintained weed free, while reducing the stress on the grass plant and the environment. At GrassRoots, we believe prevention is the best approach to a beautiful lawn!
