When it comes to managing problematic weeds such as waterhemp, we spend a majority of our time thinking about soybeans but, what is the best way to manage waterhemp in other crops such as corn?

When it comes to managing problematic weeds such as waterhemp, we spend a majority of our time thinking about soybeans but, what is the best way to manage waterhemp in other crops such as corn? When it comes to corn, we rely on many of the same herbicide groups we depend on in soybeans, such as Groups 5 and 15 herbicides. However, one advantage to managing weeds in corn is the ability to use HPPD or Group 27 herbicides. Group 27 herbicides are very effective on waterhemp pre-emerge, as well as post-emergence. Targeting weeds when they are less than four inches is the key to success with Group 27 herbicides, as they will begin to struggle once waterhemp plants become greater than four inches. Therefore, an additional effective SOA may be needed to effectively control larger waterhemp plants.

Products such as Acuron® can be used as a one-pass program. Acuron is a premix herbicide that contains two Group 27 herbicides as well as Dual II Magnum® and atrazine. This combination will result in very effective residual and postemergence waterhemp control. Applying 80 oz. of Acuron pre-emerge resulted in 87% control of waterhemp (28 DAT). Applying 40 oz. of Acuron pre-emerge followed by 40 oz. Acuron post-emergence resulted in a 12% increase in control. This increase was due to the fact that waterhemp emerges later than many other summer annuals, so some flushes of waterhemp appeared after the post-emergence application. The pre-emerge application was starting to break, and another layer of residual protection was needed. By split applying Acuron, the post-emergence application effectively controlled the waterhemp that emerged when the pre-emerge began to break, providing both post-emergence and residual activity. There are other one-pass programs, such as Corvus®, however reducing the rate in the pre-emergence application allows a post-emergence application of Capreno®. By applying a Group 27 in the optimum window for waterhemp germination, waterhemp control increased by 34%.

Bicep II Magnum® is a site of action (SOA) Group 5 and 15 herbicide that contains no Group 27 herbicide. Bicep II Magnum + atrazine followed by glyphosate and atrazine resulted in 73% waterhemp control. However, by adding Laudis®, a Group 27 herbicide, in the post-emergence application, waterhemp control increased by 21%. Applied preemerge, Verdict® (SOA 14 & 15), followed by glyphosate and atrazine, was not as effective. By adding Laudis in the post-emergence application, waterhemp control increased by 15%. The waterhemp population is suspected to be resistant to glyphosate. Waterhemp has developed resistance to glyphosate and atrazine in many parts of the mid-west, therefore, post-emergence applications of atrazine and glyphosate can have poor results depending on the waterhemp population susceptibility.

A one-pass system can be an effective program, but not all corn products are designed to be a one-pass system, especially in heavy weed pressure scenarios. Understand when your problematic weeds emerge and target with effective SOAs around this date. Programs with an HPPD in the post-emergence application resulted in a 16.4% increase in control vs. a one-pass program and post-emergence applications with no HPPDs.