When is it Too Cold to Spray Weeds in Wheat and Canola Crops?Thu, 01 Dec 2011 08:48:27 CST
With the recent rains and mild temperatures during the fall, the wheat and canola crops are well established in many parts of the state, according to Joe Armstrong, Small Grains Weed Science Extension Specialist. As well, many winter weeds, such as henbit, mustard, and the winter grasses, are also off to a good start. As we move into December, the question "How cold is too cold for herbicide applications?" is often asked.
Though there is not a perfect answer to this question, the most important thing when using any postemergence herbicide, regardless of the time of year, is that weeds must be actively growing for the herbicide to work at its best. Active growth of the crop also helps to minimize any crop injury that may occur after herbicide application. During the fall and winter, the growth rate of most weeds will become slower as the temperature gets colder.
However, despite their reduced growth, these weeds will still be susceptible to herbicide applications. A good rule of thumb for herbicide applications during the fall and winter is to wait for two or three consecutive days with high temperatures in the 50s and apply when the daily air temperature is near its peak. Along with slower weed growth, the activity of the herbicide will also be slower in colder temperatures. Though the herbicide will be working, it will take longer for the weeds to show injury symptoms than in warmer conditions.
While there is no guarantee as to how well a herbicide will work in cold temperatures, there are two important things to remember that will maximize weed control: always use the full rate of the herbicide and include any recommended surfactants or other additives. Following these suggestions will help the herbicide work to its full potential, even if the environmental conditions may not be optimal.
Our thanks to Joe Armstrong for providing this article on spraying weeds. This article was sent out as part of the OSU Department of Plant and Soil Sciences Extension News.
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