Pre emergent vs Post emergent: Which Herbicide Should I Use?

Weeds can plague even the most immaculately maintained lawn. Getting rid of these unsightly plants requires considerable effort, good timing, and, most crucially, proper application. While you may have access to various herbicides, deciding between pre emergent vs post emergent herbicides can be challenging if you lack adequate knowledge.

Go for pre-emergents to control weeds yet to emerge from the soil. Apply them from August to November to prevent winter/fall weeds. Apply post-emergents to get rid of growing or established weeds. Use post emergence in early to late spring.

What Are Pre-Emergent Herbicides?

Pre-emergent weed killers help control weeds by eliminating them before they are visible. By enveloping seeds in a protective layer, these weed killers eliminate the plant’s seeds before they can germinate and grow. The product is applied to the seedlings to prevent them from developing roots.

Usually, weeds begin to grow when the soil temperature hits anything between 55 and 60 degrees. However, pre-emergent herbicides should only be utilized when temperatures are below 60 degrees. 

Depending on your preference, the weedkiller can be used either as a spray or in granular form. Whichever way you decide to use the herbicide doesn’t matter as they work comparably.

Although pre-emergent herbicides are effective, sometimes they may not work as expected. This scenario may come to play due to photodegradation, type of soil, and water availability.

Pre-emergents rely heavily on rainfall. These weed killers need to be watered in arid regions to enhance their efficacy and ensure that the herbicides reach the turf’s soil. When adequately hydrated, pre-emergents will be effective for over eight weeks. Artrazine is an example of a pre emergence that can be used to control Bahiagrass.

What Month Should I Apply Pre-emergent Herbicides?

Pre-emergent herbicides are most effective when sprayed during the beginning of spring, late summer, or early fall. To prevent goosegrass, Crabgrass, and foxtails in summer, ensure you spray the herbicides between 15th February and 1st March.

To control deadnettle, henbit, and chickweed in winter, spray pre-emergents in late September and early October. Another indicator of when to start spraying pre-emergents is when forsythia begins to bloom in the spring. If weeds have already started to grow, abort the mission since the herbicide will be ineffective.

What Are Post-emergent Herbicides?

Post-emergents are herbicides used to control weeds that have already begun to grow. These herbicides target either the weed’s leaves or systemic roots. The weed killers typically inhibit the plant’s capacity to produce food via photosynthesis or impede the plant’s root growth. Other post-emergent weed killers cause the weed to develop rapidly and die.

Post-emergent weed killers can be administered as granules or spray, although using spray applicators may effectively kill particular weeds, including clover and dandelions. While post-emergent weed killers are most effective in weed-infested areas, these herbicides must be used carefully to prevent spray spread or contact with other plants.

Even if post-emergence herbicides successfully eliminate weeds that have sprung, they cannot manage new generations if the weeds have been permitted to produce seeds. This may cause the weed cycle to persist and the seed bank to grow.

What Month Should I Apply Post-emergent Herbicide?

Apply post-emergents during spring or between the end of summer and early fall. Throughout spring, frequent post-emergence herbicide applications are required. To prevent weeds from developing the following year, ensure you spray the post-emergent one last time in late autumn.

Is Pre-emergent or Post-emergent Herbicide Better?

Pre-emergent herbicides are used for preventative weed control, whereas post-emergents target weeds that have already grown.

Although you could argue that the pre-emergence strategy is superior since it prevents the weeds from growing, each herbicide performs different functions at different times, employing distinct methods.

Directly comparing pre emergent vs post emergent herbicides may be incorrect since each herbicide performs its tasks effectively.

Can I Apply Pre and Post-emergent Herbicides at the Same Time?

You cannot use pre-and post-emergent simultaneously. Herbicides are categorized as pre-or post-emergent based on whether they target subterranean weed seeds or emerging weeds. Due to their distinct modes of operation, it is uncommon for both to be effective simultaneously.

Early in the spring, a pre-emergent herbicide should be used before weeds have sprouted. Then, in late spring, use a post-emergence herbicide to kill weeds that have emerged or turned green. If weeds are already established in your yard, you’ve missed the pre-emergent window and must now employ post-emergent.

Pre-emergence herbicides are watered into the soil and destroy weeds before they sprout. Post-emergence herbicides are administered to weeds after they have sprouted and dried. When one herbicide is used, the other type should not be utilized.

Utilize a powerful post-emergent to clean weed-infested yards first and a pre-emergent to prevent the return of the weeds once you have overpowered them. This technique is effective and will save you time and money.

Spraying pre-emergent and post-emergent simultaneously increases effort and expense for little gain.

Is Roundup a Pre-emergent or Post-emergent Herbicide?

Roundup is a systemic post-emergent weed killer that kills annual and perennial unwanted plants. The most prevalent upsides of Round up are its control of both perennial and annual weeds and low toxicity to mammals.

This post-emergent herbicide’s greatest downside is that even minimal spray drift can severely harm some ornamentals.


Can your sprinklers be used to apply herbicides?

Using sprinklers to apply liquid weed killers may appear straightforward, but it could be disastrous. These chemicals can affect the components of your irrigation equipment. Limit your application of the herbicides to a sprayer to avoid unforeseen disasters.

Do you need to incorporate the services of a lawn mower to apply pesticides?

You don’t need a lawn mower to spray herbicides. As long as you are set with your protective gear and there are no children around, you can spray the pre-emergent or post-emergent weed killer by yourself. However, contact a professional if you doubt you can successfully pull it off.

Final Thoughts

Pre emergent vs post emergent, which herbicide should you pick? Go for pre-emergents to control weeds yet to emerge from the soil. Apply them from August to November to prevent winter/fall weeds. Use pre-emergents in mid-March to suppress summer/spring weeds.

Apply post-emergents to get rid of growing or established weeds. The ideal time to apply these herbicides is early to late spring, when most weeds are young and actively growing.

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