Stress on plants can affect the performance of all herbicides. Stress can be from cold, hot, dry or saturated, insect feeding or poor fertility.
C3 plants such as canola and wheat start to reduce metabolic activity at temperatures greater than 28°C and are pretty much disabled at 35°C. Performance for the following canola system herbicides will drop off at the given temperatures:
Glyphosate — 30°C Reference
Glufosinate — Hot temperatures can actually improve Liberty efficacy, given that hot days are also usually sunny. Humidity makes efficacy even better, Bayer says. While bronzing of canola leaves may occur, the crop will recover and the benefit is better efficacy on weeds.
Clearfield system products — 28°C Reference
NDSU provides a helpful article on herbicide applications in hot dry conditions.