Agronomy Talk

XTENDFLEX® SYSTEM - WATERHEMP CONTROL

Herbicide and Weed Management Briefs

Published on Friday, November 5, 2021

 

The XtendFlex® system allows farmers to utilize an approved dicamba formulation as well as Liberty® and glyphosate. Beck’s Practical Farm Research (PFR)® data shows that using multiple effective SOAs in the pre-emerge resulted in fewer waterhemp for the post-emergence application to control. What is the relationship between the pre-emerge application and post-emergence application? If more money is spent on the pre-emerge application, can less be spent on the postemergence application? In 2021, the Beck’s PFR team set out to determine how the pre-emergence application impacted the post-emergence application and, conversely, how the post-emergence application impacted the pre-emergence application in the XtendFlex system. This study was designed to evaluate various programs in the XtendFlex system that target heavy, medium, and low waterhemp pressure.

 

 

 

WATERHEMP CONTROL

SOA Groups 5, 14, and 15 provide very effective control of small-seeded broadleaf weeds like waterhemp. While Group 2 herbicides are very effective on large-seeded broadleaf weeds like cocklebur and morningglory; however, many waterhemp populations are resistant to this SOA group. Averaged across the various post-emergence applications, Fierce® MTZ provided the greatest waterhemp control. Authority® Elite, which includes two SOAs, also provided effective waterhemp control. When we utilized more effective SOAs in the pre-emerge with herbicides like Fierce MTZ or Authority Elite, waterhemp control never fell below 93%. Therefore, our decision in the post-emergence application was not as critical because the pre-emerge application was so successful.

 

HERBICIDES WITH TWO SOAs

When evaluating other herbicides with two SOAs, Boundary® was effective. However, residual control from metribuzin is rate-dependent and may not last as long as the Group 14 and 15s in Fierce MTZ and Authority Elite. Valor® XLT is a two SOA herbicide, but there was a good chance the waterhemp population showed some resistance due to the Group 2 component. Though Valor XLT and Boundary were less effective compared to Fierce MTZ and Authority Elite, we still had a clean program if the right post-emergence application was selected. When a post-emergence application included an in-season residual like Warrant®, control never fell below 90% when Valor XLT or Boundary was used in the pre-emergence application. Verdict®, another herbicide with two SOAs, never resulted in greater than 79% control. This can be explained by the lower residual levels within 5 oz. of Verdict. Therefore, a successful and timely post-emergence application is critical, and a second application may be needed.

 

 

ENGENIA® OR XTENDIMAX® IN THE PRE-EMERGENCE APPLICATION

Products like Engenia® and XtendiMax® have soil activity, but soil activity is not long-term residual. Therefore, Engenia or XtendiMax should be paired with an approved residual herbicide. One advantage to pairing Engenia or XtendiMax with a residual herbicide is to improve burndown activity. Many pre-emerge residual herbicides have little to no burndown activity. In the study below, the plots were clean-tilled, so only Engenia soil activity was evaluated. Once again, utilizing a pre-emerge herbicide with two or three SOAs resulted in the greatest control when paired with Engenia. If two SOAs were utilized in addition to Engenia, waterhemp control never fell below 88%. When only one SOA was utilized in the pre-emerge, the use of an in-season residual became crucial. Though Engenia has soil activity, utilizing Engenia only in the pre-emerge resulted in poor control across all the various post-emergence applications. The use of an in-season residual like Warrant® did increase control, however, it was not enough to overcome not utilizing a residual in the preemergence application.

 

WHAT IS THE BEST POST-EMERGENCE APPLICATION IN THE XTENDFLEX® SYSTEM? WE CAN MAKE ANY OF THESE HERBICIDES WORK IF WE UTILIZE THE PROPER PRE-EMERGE HERBICIDE.

Averaged across the ten pre-emerge herbicides, Warrant® increased waterhemp control by 4% when added to Liberty, 6% when added to Liberty + glyphosate, and 4% when added to Engenia + glyphosate. In-season residuals are crucial for long-term waterhemp success even when a three SOA herbicide program was utilized. However, putting the Power in the Pre™ provides more flexibility in the post-emergence application.

 

CONCLUSION:

Utilizing three effective SOAs (like Fierce® MTZ) never resulted in less than 93% waterhemp control. Therefore, we had more flexibility in the post-emergence application. Products that provide moderate waterhemp control like Boundary® and Valor® XLT are still effective if the proper post-emergence application is utilized. When an inseason residual was utilized along with at least 2 SOAs in the pre-emergence application, waterhemp control never fell below 90%. However, when no in-season residual was utilized, Boundary and Valor XLT waterhemp control fell to 85%. Engenia did provide soil activity but should be paired with an approved two or three SOA pre-emerge herbicide. When Engenia was tank-mixed with a two or three SOA herbicide, waterhemp control never fell below 88%, regardless of the post-emergence program selected. Averaged across the ten pre-emerge herbicides, Warrant® increased waterhemp control by 4% when added to Liberty, 6% when added to Liberty + glyphosate, and 4% when added to Engenia + glyphosate.

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