By Rodrigo Werle
Because of excessive and constant rainfall, many growers in eastern Nebraska were not able to make pre-emergent herbicide treatments in soybean fields this season. Now weeds are taking big advantage of that. The lack of pre-emergent herbicides along with late crop planting, warm temperatures, and plenty of soil moisture are providing the perfect conditions for weeds to thrive (Figures 1-2).
Figure 1. Commercial soybean field infested with weeds near Mead.
Figure 2. Commercial soybean field infested with velvetleaf, common waterhemp, and foxtail plants.
According to data from UNL Weed Scientist Stevan Knezevic and his colleagues (Figure 3), yield losses due to competition are already occurring and will be aggravated if growers don't eliminate these undesired plants from their fields in the near future. Therefore, weed control should be on the top priority of growers "to-do" list.
Postemergence herbicides, such as glyphosate in Roundup Ready soybeans (Group 9), ALS-inhibitors (Group 2), PPO inhibitors (Group 14), and Liberty (Group 10) in Liberty Link soybeans, are now the main options for weed control. In fields where glyphosate resistance is a problem, rescue herbicides, such as Cobra and Flextar (Group 14), should be included at this point in tank-mixes. These rescue herbicides should preferably be applied to weeds smaller than 4 inches tall. In fields where Roundup Ready volunteer corn is present, ACCase-inhibitors (Group 1), such as Select Max and Post Plus, should also be considered.
Figure 3. Influence of weed removal timing and row spacing on soybean yield loss. Researchers found yield loss increased by about 2% for each leaf stage that weeds were not controlled.
Keep in mind that the use of multiple effective herbicides will result in effective weed control and assist growers on the fight against herbicide-resistant weeds.
Source: unl.edu