Pre-Emergent Herbicides: Setting Up for Effective Weed Control this Spring
When applied at the correct time, pre-emergents can significantly reduce weed pressure, improve turf quality and reduce the need for follow-up post-emergent applications.
Pre-emergent herbicides are one of the most valuable tools available to turf managers. Rather than controlling weeds after they emerge, these products create a barrier in the soil that prevents weed seedlings from establishing.
As resistance issues increase post emergent herbicides are less effective making a pre-emergent plan essential. With a range of products available, understanding the differences in longevity, turf safety and application requirements can help turf managers select the right option for their site.
Common Pre-Emergent Herbicides and How They Work
Although pre-emergent herbicides all aim to stop weed establishment, they do so in very different ways.
Root development
Products such as Barricade®, Stomp Xtra®, and Revere 500® primarily prevent new root development in germinating weeds. Without a functioning root system, seedlings starve and quickly die. These products remain the backbone of many turf weed control programs due to their reliability and long residual activity.
Residual control
Specticle® works differently from many traditional pre-emergent herbicides and provides some of the longest residual control available in turf. In addition to preventing new weed establishment, it can provide activity on very young emerging weeds when applied at the correct timing.
Common Pre-Emergent Herbicides and How They Work
| Product | Active Ingredient | Typical Control Period |
| Propyzamide | 4-6 weeks | |
| S-metolachlor | 6–8 weeks | |
| Dimethenamid-P | 8–12 weeks | |
| Oxadiazon | 8-10 weeks | |
| Pendimethalin | 6-8 weeks | |
| Prodiamine | Up to 6 months (rate dependant) | |
| Indaziflam | Up to 8 months (rate dependant) |
Getting the Timing Right
The most important rule with pre-emergent herbicides is simple, they must be applied before weeds emerge.
For summer weeds, applications are typically made in late winter or early spring before soil temperatures increase.
Summer grass
For winter weeds such as annual winter grass (Poa annua), applications are generally made during late Summer to early Autumn before germination begins.
Winter grass
Longer residual products can provide protection for many months, while shorter residual products may require repeat applications throughout the season. Planning ahead and matching the product to your target weeds is essential for consistent control.
Turfgrass Safety Considerations
Not every pre-emergent herbicide is suitable for every turf species or situation. Some products are better suited to warm-season turf, while others may have restrictions on cool-season species or newly established turf. Always check the product label before application.
It is also important to consider future renovation plans. Depending on the product used, reseeding restrictions can range from a few weeks to several months. Applying a long-residual herbicide before an overseeding or renovation program can lead to establishment issues later in the season.
How to Maximise the Benefits of Pre-Emergent Herbicides
Even the best pre-emergent herbicide will struggle if it is not applied correctly. The following practices will help maximise performance:
1. Apply well before germination
Pre-emergents are preventative products. Once weeds have emerged, control is significantly reduced.
2. Water-In as directed
Many pre-emergent herbicides require irrigation shortly after application to move the active ingredient into the soil profile where weed seeds germinate. Always follow label recommendations for irrigation timing and volume.
3. Avoid soil disturbance
Practices such as coring, deep verticutting or aggressive cultivation can disrupt the herbicide barrier and allow weeds to establish.
4. Match the product to the site
Consider factors such as turf species, target weeds, desired control period and renovation schedules when selecting a product.
5. Rotate herbicide groups
Rotating between different herbicide groups can help reduce the risk of herbicide resistance and support long-term weed control programs.
Successful weed control begins long before weeds appear. By selecting the correct pre-emergent herbicide, applying it at the right time and following best-practice application techniques, turf managers can achieve cleaner surfaces, reduce in-season weed pressure and improve overall turf quality. While every site is different, a well-planned pre-emergent program remains one of the most effective investments in year-round turf management.
Living Turf Technical Services have developed soil temperature and moisture models that define when weed germination will occur for many different weed species. This is valuable in ensuring you get the timing right to get the best control with the longest residual to maximise your return on money spent. Contact your Living Turf Sales Agronomist for advice.