2, 4-D and Dicamba Effects on Soybean Nodulation and Yield.

Soybean is extremely sensitive to auxin type herbicides, with injury symptoms evident in shoot growth when applied at extremely low rates. Soybean varieties now have been developed which are resistant to either 2, 4-D or dicamba but not both. In the future these resistant varieties will be planted in fields next to non-resistant types. Due to this close proximity, there may be more drift or tank contamination problems onto non-target soybeans. Herbicides containing 2, 4-D or dicamba mimic auxin, a plant growth hormone, which has been shown to reduce nodulation in soybeans. We hypothesized that soybean nodulation would be reduced when treated with simulated drift rates of 2, 4-D or dicamba. This field study examined the effect of 2, 4-D and dicamba applied at different timings on soybean nodulation and yield. In addition, foliar nitrogen was applied at two different times after herbicide applications, as a rescue treatment, to determine if herbicide effects could be minimized.