Pre-Emergent & Post-Emergent Best Practices for Fall
Fall is one of the most important seasons for weed control, yet many homeowners focus only on spring applications. The truth is that some of the most problematic lawn weeds germinate, grow, and establish themselves in the fall. A proactive fall weed control plan can dramatically reduce weed pressure next spring and help your lawn enter winter stronger and healthier.
The key is knowing when to apply a pre-emergent herbicide versus a post-emergent herbicide. While both products fight weeds, they work in completely different ways. Understanding the difference can help you build an effective lawn care program no matter where you live.
Pre-Emergent vs. Post-Emergent
A pre-emergent herbicide prevents weeds before they emerge from the soil. Once applied and watered in, it creates a barrier that stops newly germinated weed seedlings from becoming established. Pre-emergents do not kill existing weeds. Instead, they prevent future weeds from growing. Fall pre-emergents are especially useful for preventing winter annual weeds such as Poa annua (annual bluegrass), Chickweed, Henbit, Shepherd's purse and Speedwell. If these weeds are a problem in your lawn every spring, there's a good chance they began germinating the previous fall. Learn more about pre-emergents.
A post-emergent herbicide is designed to kill weeds that are already growing and visible in the lawn. These products are absorbed through the leaves and move throughout the plant to control the weed. Common weeds controlled by post-emergent herbicides include dandelions, clover, plantain, chickweed, wild violet, ground ivy and thistle. Products such as weed & feeds, like Surge® Weed & Feed 16-0-9, use post-emergent herbicides to control actively growing broadleaf weeds while also providing nutrients to the lawn. Learn more about post-emergents.
Fall Weed Control for Cool-Season Lawns
If you're trying to prevent winter annual weeds like poa annua and chickweed, apply a pre-emergent in late summer through early fall before weed seeds germinate. The ideal time to apply is right before soil temperatures drop below 70 degrees Farenheit consistently. A fall application of a product such as Barricade® helps prevent weeds from becoming established during the cooler months. Use a fall pre-emergent if poa annua is a recurring problem, you have a history of winter annual weeds, you are not planning to overseed, or you want fewer weeds next spring.
Many cool-season homeowners overseed in the fall. Because pre-emergent herbicides prevent seed germination, most traditional pre-emergents can interfere with new grass seed establishment. If you're planning a fall renovation or overseeding project, carefully read product labels and build your weed control plan around your seeding schedule. Learn more: "Can I Apply Pre-Emergent and Seed at the Same Time?".
Fall is often the best time of year to control established broadleaf weeds. As temperatures cool, weeds begin storing nutrients in their roots for winter survival. When a post-emergent herbicide is applied during this period, the weed pulls the herbicide deeper into the root system, frequently resulting in better long-term control than spring applications. A fall post-emergent application can significantly reduce spring weed populations.
Fall Weed Control for Warm-Season Lawns
Fall pre-emergent applications are critically important for warm-season lawns. As bermuda and other warm-season grasses enter dormancy, winter weeds begin germinating and can quickly take over thin turf. For many southern homeowners, fall is actually the most important pre-emergent application of the year. Use a fall pre-emergent is your bermuda lawn fills with winter weeds every year, you battle poa annua, you want cleaner turf during winter dormancy, or you want fewer weeds competing with spring green-up.
A fall post-emergent application can also be highly effective in warm-season lawns if weeds are actively growing. Apply before extended cold temperatures arrive and while weeds are still metabolically active.
Should You Apply Both?
If you currently have weeds growing and want to prevent additional weeds from emerging, use a post-emergent to control existing weeds and follow with a compatible pre-emergent application to prevent future weeds.
If your lawn currently has very few weeds, focus on a pre-emergent application and continue proper mowing and fertilization practices.
If dandelions, clover, and other broadleaf weeds are widespread, prioritize post-emergent control first and then evaluate whether a fall pre-emergent fits into your lawn care program.
Always follow label instructions regarding application timing and intervals.
Fall Weed Control Mistakes to Avoid
- Applying pre-emergent too late. Once weeds have germinated, pre-emergents cannot control them.
- Applying post-emerent to dormant weeds. Post-emergent herbicides work best when weeds are actively growing.
- Forgetting about fall weed control. Many homeowners wait until spring to address weeds. By then, many winter annual weeds have already become established.
- Using pre-emergent before overseeding. Traditional pre-emergents may prevent desirable grass seed from germinating.
The Best Fall Weed Control Strategy
For most homeowners, the ideal approach is:
- Identify existing weeds.
- Use a post-emergent herbicide if weeds are actively growing.
- Apply a fall pre-emergent to prevent winter annual weeds.
- Fertilize according to your grass type and region.
- Continue proper mowing practices until growth stops.
Use pre-emergents to stop weeds before they germinate. Use post-emergents to eliminate weeds that are already growing. Whether you have a cool-season lawn in Ohio or a warm-season lawn in Georgia, fall weed control can dramatically improve lawn performance next year.
