Updated September 23, 2020:
Experiment 1: Effectiveness of weed control programs for management of multiple-resistant waterhemp in LibertyLink GT27 soybean
LibertyLink GT27 ‘CZ 2360’ soybean were planted in 30 inch rows. Following planting, 15 different PRE herbicide treatments were applied. Waterhemp control was monitored throughout the season. Liberty + glyphosate and Liberty alone were applied when the majority of the PRE treatments needed a POST herbicide application for waterhemp control. Waterhemp control is still currently being monitored.
Initial results and observations:
• There was significant variation in the initial control and the length of residual activity for the different soil-applied herbicides.
• At the time of the POST application, only Dimetric Charged, Authority MTZ, Zidua, Dual II Magnum, Warrant, Outlook, Alite + Zidua, Fierce, Authority Edge, and Fierce MTZ provided 90% or greater waterhemp control.
• Metribuzin alone was the least effective (60%). Waterhemp control with Alite, Valor and Spartan were similar, ranging from 80-88%.
• After the POST Liberty + glyphosate or Liberty alone application all treatments provided greater than 90% waterhemp control, with the exception of the PRE metribuzin. Exhibiting the importance of having a good residual herbicide in the PRE treatment.
Experiment 2: Effectiveness of weed control programs for management of multiple-resistant waterhemp in Enlist E3 soybean
Pioneer 25T09E soybean were planted in 30 inch rows. Following planting, PRE treatments of Valor were applied on half of the study. Approximately 56 DAP, POST treatments of Enlist Duo, Liberty, Enlist One + Liberty, and Roundup were applied. Waterhemp control continues to be monitored throughout the season.
Initial results and observations:
• Treatments with Valor PRE averaged ~65% control of waterhemp at the time of POST.
• Waterhemp control was greatest with Enlist Duo and Enlist One + Liberty 14 d after the EPOS timing. Control with Liberty only averaged 78%. High populations of waterhemp that limited Liberty coverage and dry temperatures resulted in lower than normal control with Liberty.
• Starting with a PRE herbicide application helped late season waterhemp control with Liberty. However, this year the inclusion of the choline salt of 2,4-D in Enlist One or Enlist Duo helped improve control.
• The addition of Dual II Magnum, Outlook, or Warrant with POST treatments did not reduced waterhemp control and we will continue to monitor waterhemp for end of season control.
• Waterhemp can be effectively controlled in Enlist E3 soybean, the option of including 2,4-D or 2,4-D + Liberty in the POST application is an added benefit.
Experiment 3: Waterhemp control in XtendFlex soybean
XtendFlex soybean were in 30-inch rows. Preemergence applications of Valor were made to 11 of the 20 treatments immediately after planting. Postemergence applications were made on August 12. EPOS applications were made on August 6 and LPOS applications were made on August 25. All treatments were compared with an untreated control. Soybean injury and waterhemp control were evaluated throughout the season. Additionally, waterhemp will be counted 21 DAT from two 0.25 m2 quadrats per plot. Additional weed counts and biomass harvests will take place from two 0.25 m2 quadrats per plot at peak biomass.
Initial results and observations:
• Valor PRE caused some initial soybean injury and provided between 80-100% waterhemp control at the time of POST application, 49 DAP.
• Glyphosate EPOS provided the no control of waterhemp, demonstrating the importance for effective sites of action to be used POST.
• At 21 days after EPOS, applications of XtendiMax + glyphosate and Liberty + glyphosate provided 95-98% control of waterhemp while applications of Liberty alone provided 84-90% control of waterhemp.
• This year, applications of Liberty + XtendiMax did not result in reduced control in the time period after application. In 2019, waterhemp control was slightly reduced shortly after application, demonstrating a potential antagonistic response.
• Greenhouse studies and non-crop field studies are being evaluated for potential interactions in the XtendFlex chemical system.