![]() When the temperature is below 40☏ for an extended time after burndown herbicide application, weed control will most likely be reduced, specifically for a systemic burndown herbicide such as glyphosate. ![]() Herbicides applied in the fall will NOT provide control of summer annual weeds such as common waterhemp or palmer amaranth because they do not emerge until May. When the temperature is below 60☏, absorption of herbicides such as glyphosate and translocation of herbicides such as 2,4-D are lower compared with applications at higher temperature therefore, they act slowly. Herbicides can be applied at temperatures of 40☏ to 60☏, but weeds may be killed slowly. The i deal temperature for applying most post-emergence herbicides is between 65☏ and 85☏ however, that window is not always practical with other fall practices. The likelihood of reduced weed control due to cool temperatures will vary depending on the target weed, herbicide, and rate of application. With seasonally low air temperatures at this time, growers have asked about how temperature will affect the efficacy of fall burndown herbicide applications. Effect of Temperature on Herbicide EfficacyĬorn and soybean harvests were late this year due to rains in September and October and fall burndown applications were delayed in much of the state. Marestail can emerge in the fall and in the spring however, most marestail in Nebraska is fall emerging and more effectively controlled in the fall when it's in a seedling stage. Tank-mixing a residual herbicide with a burndown product will improve marestail control because the residual activity will control marestail emerging after herbicide application. A recent survey reported that more than 2 million acres in Nebraska is infested with herbicide-resistant marestail. Most marestail in Nebraska is resistant to glyphosate and the ALS group of herbicides (Classic®, Permit®, Pursuit®, and Raptor®) and is challenging to control with only a glyphosate burndown program. ![]() Marestail is a significant problem weed in Nebraska. For example, if you see a lot of marestail, a fall herbicide application is needed. That's why field scouting is important before you decide about herbicide application. Herbicide timing to achieve the most effective control varies according to the weed species present. (For more information see Identification of Winter Annual Weeds, Nebraska Extension EC 304.)įall herbicide application is not needed in each field. Identification of winter annual weeds is important to select the proper herbicide for effective management. The most common winter weeds in Nebraska are marestail, henbit, field pennycress, prickly lettuce, shepherd’s-purse, downy brome, tansy mustard, and dandelion. As fall temperatures will continue to drop, it is important for growers to decide as soon as possible about applying herbicides this fall. Recently we received several phone calls about control of winter annual weeds in the fall and how temperature and frost might affect herbicide efficacy. ![]()
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