Pre‑emergent herbicides prevent annual weed seeds from germinating. Timing is critical for success, but proper selection and application techniques are just as important. According to the University of Kentucky’s turf care calendar, pre‑emergent products should be applied by mid‑April in central Kentucky publications.ca.uky.edu. A second application in late May may be necessary for grasses like goosegrass and foxtails publications.ca.uky.edu. Crabgrass, goosegrass and foxtail seeds begin sprouting when soil temperatures reach 55–60 °F muhlenberg.ca.uky.edu, so keep an eye on soil thermometers or phenological cues like forsythia bloom. The following tips will maximize your results:
- Know your weeds: Crabgrass, goosegrass and foxtails germinate when soil temperatures reach 55–60 °F. Pre‑emergent herbicides create a barrier that prevents these seeds from sprouting.
- Apply before seeds germinate: In Louisville, aim to apply pre‑emergent in late March or early April when forsythia bushes bloom (a natural indicator). For northern suburbs, apply by April 15 publications.ca.uky.edu.
- Split applications: A second application 6–8 weeks later helps extend control through summer publications.ca.uky.edu. Avoid pre‑emergent herbicides if you plan to overseed, as they inhibit grass seed germination.
- Avoid weed & feed: Spring “weed & feed” combinations can encourage disease and weed problems publications.ca.uky.edu. Instead, fertilize in fall and apply pre‑emergent separately.
- Water in: After applying granular pre‑emergent, lightly irrigate (about ½ inch) to activate the product and create a uniform barrier.
Choosing and Applying Products
- Active ingredients: Common pre‑emergent herbicides for home lawns include dithiopyr, prodiamine and pendimethalin. Each has a different window of residual activity. Read the label for proper rate, and never exceed the maximum annual amount.
- Calibrate your spreader: Measure your lawn area and calibrate the spreader to deliver the correct amount of product. Too little won’t control weeds; too much can harm turf and nearby ornamentals.
- Overlap carefully: When applying pre‑emergent, walk at a steady pace and slightly overlap passes to avoid gaps where weeds can emerge. Sweep excess granules off sidewalks and driveways to prevent runoff.
- Timing adjustments: Because Louisville’s climate can vary from year to year, base your timing on soil temperature and weather patterns rather than the calendar alone. Use a soil thermometer or ask your local extension office for current readings.
Special Considerations
- Avoid seeding windows: Pre‑emergent herbicides inhibit all seeds, including desirable grass seed. If you plan to seed or overseed, skip pre‑emergent and rely on cultural practices and spot treatments to manage weeds until the new turf is established.
- Combine with other practices: Pre‑emergent herbicides prevent new weeds but do not affect existing weeds. Combine applications with proper mowing, fertilization and overseeding to thicken turf and reduce weed pressure. For more weed control strategies, see our Preventing Weeds in Louisville Lawns article.
- Environmental stewardship: Rainfall or irrigation activates pre‑emergents, but heavy rain soon after application can dilute or wash the barrier away. Avoid applying before forecasted downpours. Sweep or blow granules off hard surfaces to prevent contamination of storm drains and waterways.
Proper timing and application ensure your Louisville lawn stays free of annual weeds. For precision treatments, consult Rise Pest Pros for professional lawn care services.
