Managing Late-Emerging Weeds in Soybean

June 23, 2000 Deciding whether a specific weed infestation is worth treating is usually based on a subjective evaluation of the potential impact of the infestation on crop yields. The two main criteria used are 1) the number of weeds present, and 2) the specific weeds present (foxtail, velvetleaf, etc.). Another factor that is just as important, if not more so, is the emergence date of the weed in relation to the crop. Crops and weeds compete for limited resources (light, moisture, nutrients), and plants that initially capture the resources usually will have an advantage over slower developing plants for the entire growing season. Weeds that emerge more than a week after the crop are at a competitive disadvantage with the crop and less likely to have an economic impact. Thus, relative time of emergence needs to be considered when evaluating the potential impact of weeds on crop production.