Pre-Seed Cold Temperature Guidance

Written by: Patty Soloducha - Technical Sales Agronomist North/Central Sask

Successful herbicide performance depends heavily on environmental conditions, especially temperature. Cool nights, frost events, and plant stress can all influence how effectively weeds absorb and respond to herbicide applications. Understanding when to spray — and when to wait — can significantly improve weed control and reduce the risk of poor performance or regrowth.

Ideal Application Conditions

Best case: 

• 1–2 warm, sunny days with temps ≥ 8-10°C
• Nighttime lows ≥ 4°C before application
• Helps improve control of larger or tougher weeds

Minimum Temperature Guidelines

• If temperatures drop below 0 to −3°C: 
  • Wait until air temperature reaches ≥10°C
  • Spray after at least 2 hours at this temperature
  • Ensures weeds return to active growth
• Stop spraying if: 
  • Temps are forecast to fall ≤ 8°C
  • End applications at least 2 hours before the temperature drop

After a Hard Frost (Below −3°C)

• Assess weed damage before spraying: 
  • Look for water‑soaked or blackened leaves
• Wait 24–48 hours before resuming applications
• If >40% leaf damage, follow Canola Council guidance: 
  • Wait until new green growth appears
• Spray only on a warm rebound day

Product Performance Considerations

• Some active ingredients are more temperature sensitive. Cold, drought, or heat stress can: 
  • Harden weeds
  • Reduce control or suppression
  • Increase chance of regrowth

GO / CAUTION 

GO (Generally):

• Overnight low > −3°C
• Weeds look healthy
• Daytime temps warming to ≥8–10°C
• Spray during warming conditions

CAUTION:

• Repeated near‑freezing nights
• Slower symptom development
• Systemic products may take longer to show results

Simple Decision Matrix

Overnight Low ABOVE −3°C — proceed if ALL apply:

• No frost on leaves; foliage dry
• No visible frost injury
• Day will warm to ≥8°C (ideal 8–10°C+) for several hours post‑spray

Overnight Low BELOW −3°C — delay & reassess:

• Wait 24–48+ hours
• Confirm ≥60% green tissue and new growth
• Spray only on a warm rebound day
• Avoid if another hard frost is forecast

Temperature plays a critical role in herbicide effectiveness. Spraying during warm, stable conditions improves weed uptake, enhances control, and reduces risk. After frost events or periods of cold stress, patience is often the best management tool. Waiting for weeds to recover and resume active growth can make the difference between effective control and costly regrowth later in the season.