While the registration of 2,4-D and dicamba products for over-the-top use in resistant-varieties has improved waterhemp control for many farmers, weed scientists warned that these herbicides would eventually select for resistant waterhemp populations. Bayer recently reported the discovery of two likely dicamba-resistant waterhemp populations in Iowa, which warrants a discussion on best management practices to slow the evolution of resistant waterhemp populations.
The particulars
On Friday, September 1, Bayer released an external communication reporting that suspected dicamba-resistant waterhemp populations were sampled in Scott County in 2021 and Marshall County in 2022. After extensive screening the company states they are likely resistant to dicamba but will continue testing to positively confirm the resistance. This is the first case of plant growth regulator (HG 4) resistant waterhemp in Iowa, though other states have already documented HG 4 resistance in their own waterhemp populations. HG 4-resistant waterhemp were documented by university researchers in Nebraska in 2009, Illinois in 2016, and Missouri in 2018.
This discovery is not a cause for panic, but it is an important reality check for farmers who rely heavily on HG 4 herbicides or any other individual herbicide group for waterhemp control. Waterhemp is known for its ability to quickly adapt to herbicide management tactics; Iowa State University has already officially documented resistance to five HGs in Iowa waterhemp populations
Source: iastate.edu
Categories: Iowa, Crops