Crabgrass Prevention and Timing

Applying crabgrass preventative in spring is critical because crabgrass is an aggressive annual weed that can quickly dominate thin or stressed turf areas. Even with good cultural practices—like proper mowing, fertilization, and irrigation—crabgrass can still invade because its seeds are abundant and germinate under favorable conditions.

Why is Crabgrass Preventative Important?

• Crabgrass germinates early and grows fast: Once established, it competes for water, nutrients, and sunlight, weakening desirable turf.
• Preemergence herbicides stop the problem before it starts: Products like Prodiamine and Dithiopyr (Dimension) prevent seeds from germinating by inhibiting cell division.
• Timing is everything: These herbicides only work on germinating seeds, so they must be applied before crabgrass emerges.

How to Apply Crabgrass Preventative Effectively

1. Choose the right product. Prodiamine and Dithiopyr are the industry standards for season-long control. Dithiopyr also offers early post-emergent activity if crabgrass has just sprouted.  
   
   
2. Apply the correct rate. Rates vary by region, turf density, and whether you use a split application. Warmer climates or weaker turf often require higher rates.
   
   
3. Apply at the right time. Application timing is based on soil temperature or by using the GDD tracker for accuracy (https://gddtracker.msu.edu/). Crabgrass germinates when soil temps reach 55–60°F for 7–10 days.
   
   Example Timing:
   Northern IL/IN/IA: Late March-early April
   Southern WI: Mid-late April
   Central/Southern IL/IN" Mid-Late March (consider split applications with second application in mid-May)
   
   
4. Water. Herbicides must be activated by rainfall or irrigation before germination.

PRO TIP: Pair preemergence with strong cultural practices (proper mowing height, fertilization, overseeding) for best long-term results.