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Hannah Mathers, Ohio State University Extension, Horticulture and Crop Science |
Postemergent herbicides generally perform best at warmer air temperatures. The major effect of temperature is on rate of uptake of the herbicide. High temperatures favor rapid uptake, and generally favorable weed control can be obtained if the temperature is high at the time of application.
Not only does temperature affect herbicide uptake but temperature can also have a pronounced effect on dissipation or losses of herbicide from soils through volatilization and degradation (Fritz and Smith, 1975). Treflan for example, evaporates readily and vaporizes rapidly at high temperatures. The volatilization losses of Treflan can be reduced by cultural practices such as physical incorporation into the soil. Generally, the quicker a volatile herbicide is incorporated into the soil after application the better.
The volatility of herbicides also influences their extent of application in established nursery stock. Casoron, as an example, is so volatile at soil temperatures above 50F, that its use is limited to late fall, winter, and early spring applications.