Critical Weed-Free Period & Weed at the Right Time
Times weeding
Enter the sowing date and the crop's critical window to get the period start, end and duration— so you weed at the right time and protect yield.
Critical weed-free period
Next: schedule weeding / herbicide so the crop is clean from Jun 21, 2026 through Jul 16, 2026; one or two well-timed passes in this window protect most of the yield.
The exact window depends on crop, variety, spacing and weed pressure — treat these DAP figures as a planning guide and adjust to local recommendations.
Critical weed-free period — key facts
- Window dates
- sowing date + start/end days
- Typical window
- ≈ 20–45 days after sowing
- Before window
- weeds cost little if cleared
- After window
- canopy shades late weeds out
- Goal
- clean field through the window
- Varies with
- crop, spacing, season, pressure
- Pays off most
- one well-timed weeding
- Privacy
- Runs in your browser; nothing uploaded
Weed when it counts, skip when it doesn't
Not every weed costs you yield. Every crop has a critical window — often roughly 20 to 45 days after sowing — when it is most vulnerable to competition for light, water and nutrients. Weeds before that window do little harm if cleared by its start, and weeds after it arrive too late to matter once the canopy closes. Keeping the field clean through this one window captures nearly the full yield benefit for the least labour and chemical.
This tool turns your sowing date and the crop's critical-period days into the window start, end and duration, so you can schedule weeding or a residual herbicide precisely. Aim to enter the window clean and hold it clean to the end date. Pair it with the Herbicide Plant-Back, Weed Yield Loss and Spray Schedule tools for a complete weed-management plan.
Time your weeding
Get the exact window dates from sowing.
Protect the yield
Stay clean through the vulnerable stage.
Save labour
Skip weeding that comes too late to help.
Plan one pass
A well-timed weeding captures most gain.
Frequently Asked Questions
What is the critical weed-free period?+
The critical weed-free period (CWFP) is the window in a crop's growth — often something like 20–45 days after sowing — when it must be kept free of weeds to protect yield. Weeds present before this window do little harm, and weeds emerging after it compete too late to matter much, but weeds during it cause the biggest yield loss.
How is the window calculated?+
From the sowing date plus the start and end days of the critical period. If sowing is 1 June and the crop's window is 20–45 days, the period runs from about 21 June to 16 July, a 25-day weed-free window. The tool gives the start date, end date and duration so you can schedule weeding.
Why does timing matter so much?+
Weeds compete with the crop for light, water and nutrients, but a crop is most vulnerable during a specific growth stage. Controlling weeds only within the critical period delivers nearly the full yield benefit for the least effort — weeding outside it wastes labour and chemicals for little extra return.
What happens to weeds before the window?+
Weeds that emerge before the critical period generally cause little yield loss as long as they are removed by the start of the window, because the crop is small and not yet limited by competition. The key is to enter the critical period clean — one early control pass usually achieves that.
What about weeds after the window?+
Weeds emerging after the critical period end usually compete too late to reduce yield much, since the crop canopy has closed and shades them out. They may still cause harvest problems or seed the field for next year, but their effect on this crop's yield is small.
Does the window differ by crop?+
Yes — every crop and even variety has its own critical period, varying with spacing, vigour, season and weed pressure. Wide-row, slow-canopy crops have longer windows; vigorous, quick-canopy crops have shorter ones. Use the figures from local research or extension guidance for your crop and enter them here.
How do I use the result in the field?+
Aim to have the field clean by the period start and keep it weed-free through to the period end — that is when one or two well-timed weedings or a residual herbicide pays off most. After the end date, the crop's canopy largely suppresses new weeds, so further weeding is usually optional.
Can I just weed once?+
Often a single, well-timed weeding within the critical period captures most of the yield benefit, and a residual herbicide applied early can hold the field clean through the whole window. The right number depends on weed pressure and crop, but timing matters more than frequency.
Are the figures precise?+
They are accurate for the window you enter, but the real critical period shifts with weed density, species, weather and crop vigour, so treat it as a guide. Scout the field, keep it clean through the window, and adjust the dates if the crop or weed pressure differs from expectation.