Pre-emergent herbicides are a valuable tool in preventing the growth of various weed types before they emerge from the soil. These herbicides work by forming a chemical barrier on the soil surface, inhibiting seed germination. Understanding which weeds can be controlled by pre-emergent herbicides helps in effectively managing your lawn or garden.
What Weeds Do Pre-emergent Herbicides Control?
Pre-emergent herbicides are effective against a range of annual grassy and broadleaf weeds. They are particularly useful for controlling weeds like crabgrass, foxtail, and chickweed. These herbicides are applied before the weeds germinate, usually in early spring or fall, depending on the weed type.
Common Weeds Controlled by Pre-emergent Herbicides
- Crabgrass: A notorious summer annual grass that thrives in warm conditions. Pre-emergents are typically applied in early spring before soil temperatures reach 55°F.
- Foxtail: Another annual grass that can invade lawns and gardens, often controlled with spring applications of pre-emergents.
- Chickweed: A winter annual broadleaf weed that can be controlled by applying pre-emergents in the fall.
- Poa annua (Annual Bluegrass): This cool-season annual grass is best controlled with fall applications of pre-emergent herbicides.
- Henbit: A common broadleaf weed that emerges in the fall and is controlled by fall pre-emergent applications.
How Do Pre-emergent Herbicides Work?
Pre-emergent herbicides work by creating a barrier in the soil that affects the early stages of weed seed germination. They do not kill existing weeds but prevent new ones from growing. For optimal results, these herbicides need to be applied before the weed seeds germinate and should be watered in to activate the chemical barrier.
When to Apply Pre-emergent Herbicides?
Timing is crucial for the effectiveness of pre-emergent herbicides. Application should be done before weed seeds germinate:
- Spring Application: Generally, apply when soil temperatures consistently reach 50°F to 55°F. This is typically when forsythia blooms.
- Fall Application: For winter annuals, apply when soil temperatures drop below 70°F in late summer or early fall.
Types of Pre-emergent Herbicides
There are several types of pre-emergent herbicides available, each with different active ingredients targeting specific weeds. Here’s a comparison of some popular options:
| Feature | Prodiamine (Barricade) | Dithiopyr (Dimension) | Pendimethalin (Pre-M) |
|---|---|---|---|
| Price | $$ | $$ | $$ |
| Weed Control | Crabgrass, Poa annua | Crabgrass, foxtail | Crabgrass, chickweed |
| Application | Spring/Fall | Spring/Fall | Spring |
| Duration | Up to 6 months | Up to 4 months | Up to 3 months |
How to Apply Pre-emergent Herbicides
- Preparation: Clear the area of debris and mow the lawn if necessary.
- Application: Use a spreader for even distribution.
- Watering: Lightly water the area after application to activate the herbicide.
People Also Ask
How Long Do Pre-emergent Herbicides Last?
Pre-emergent herbicides typically last between 3 to 6 months, depending on the product and environmental conditions. Factors like heavy rain or frequent irrigation can reduce their effectiveness.
Can Pre-emergent Herbicides Harm My Lawn?
When used as directed, pre-emergent herbicides are safe for established lawns. However, they can prevent grass seed germination if applied before seeding. Always follow label instructions to avoid damage.
Are There Organic Pre-emergent Herbicides?
Yes, corn gluten meal is an organic option that can act as a pre-emergent herbicide. It is less effective than chemical options but can suppress some weed growth.
Do Pre-emergent Herbicides Control Perennial Weeds?
Pre-emergent herbicides are not effective against perennial weeds, as they primarily target germinating seeds. For perennials, post-emergent herbicides or mechanical removal may be necessary.
Can I Apply Pre-emergent Herbicides in the Rain?
Light rain can help activate pre-emergent herbicides, but heavy rain may wash them away, reducing effectiveness. It’s best to apply them when moderate rain is expected or water them in lightly.
Conclusion
Pre-emergent herbicides are a proactive approach to weed management, effectively controlling a variety of annual weeds before they emerge. By understanding the types of weeds they control and the correct application timing, you can maintain a healthy, weed-free lawn or garden. For more guidance on lawn care, consider exploring related topics such as post-emergent herbicides and lawn maintenance tips.