When to Use Post-Emergent Herbicides

Post-emergent herbicides are weed killers that kill existing, mature, and fully grown weeds. (The weeds have already emerged, thus the killer is post-emergent.) While some post-emergent herbicides will not cause damage to surrounding ground cover when applied, others should be applied directly to the weed only. Otherwise, you risk killing all vegetation and not just the weeds. Some post-emergent herbicides are systemic, formulated to work throughout an entire plant all the way down to its root system. Here is some additional valuable information about knowing when to use post-emergent herbicides:

• Side effects. Make sure that you are aware of the ramifications of applying a post-emergent herbicide broadly since some groundcover, flowering vegetation, and other plants are susceptible to damage.
• Directions. Read the directions and cautions listed on the product label before using a post-emergent herbicide and protect frail and susceptible plants before using it.
• Wind. Since chemicals can drift on a breezy day, make sure that you use a post-emergent herbicide only on days where you anticipate little or no wind. Otherwise, chemicals will drift into neighboring yards or into plants that will be damaged by the herbicide.
• Brush. If you've resistant weeds, consider using a paint brush to brush the post-emergent herbicide directly onto the plant, its leaves and stalk, and at the surface level. That way, the herbicide will travel the length of the plant, including into the root system far below the ground surface.
• Grains. While you can purchase granular formulas of post-emergent herbicides, liquid forms are the preferred delivery method, since the liquid can slide down the stalk of established weeds and infiltrate the root system.

You could forego the need to ever use a post-emergent herbicide if you use a pre-emergent chemical effectively. But, since many of us sometimes miss the window of opportunity presented us in the pre-spring season to effectively apply a pre-emergent herbicide, keeping a supply of post-emergent chemical on hand will help control the weed population into late summer and early fall.