Extension Logo
Extension Logo
University of Minnesota Extension
https://extension.umn.edu

Extension is expanding its online education and resources while in-person events and classes are canceled.

Managing waterhemp with layered residual herbicides

Got waterhemp? Layer residual herbicides to maintain control

Waterhemp is increasingly difficult to manage, as it’s becoming more widespread and herbicide-resistant populations are expanding, including multiple-resistant populations.

In addition, it has a long emergence pattern and frequently outlasts control of an early preemergence herbicide application.

One strategy is to layer residual herbicides which helps control glyphosate-resistant waterhemp by extending the duration of seedling control. In fact, research has shown this strategy can provide season-long control for Minnesota soybean.

Research: Layering herbicides for waterhemp control in soybean

 | 

Study findings

In July, weed control evaluations clearly showed an advantage of the two-pass system over single applications of residual herbicides (Figure 2). Figure 2 below shows a comparison of weed control in soybean with a single preemergence application of Outlook (left) and layered applications of Outlook on May 5 and June 8 (right). Photos taken July 14.

weed control in soybean
Single preemergence application of Outlook
weed control in soybean
Layered applications of Outlook on May 5 and June 8

Extended control

The season-long control of the layered or preemergence application followed by a postemergence application (PRE/POST) persisted through the end of the season, while control in the PRE-only treatments continued to diminish (Table 1). By the end of September, waterhemp control was 90 to 95 percent in the two-pass system, compared to 62 to 81 percent in the single PRE application system.

Increased yield

Yields reflected the weed control results with a 10 bushel average difference between the layered and single PRE applications. The yield range of the layered herbicide treatments was 46 to 51 bushels per acre, while the PRE-only treatments ranged from 32 to 43 bushels per acre.

While waterhemp is a challenging weed to manage, this trial demonstrates that layering effective residual herbicides is a strategy that could provide season-long control in Minnesota.

View the full report

Table 1 shows yields after a residual herbicide was applied either PRE only (after planting, on May 5, 2015) or layered PRE/POST (May 15 and June 8, 2015) in Rochester in 2015. Notes:

  • All PRE treatments included 4 fluid ounces of Pursuit per acre.

  • Waterhemp density on June 8 was 51 per square feet in Pursuit check.

  • The Pursuit weedy check yield was 14 bushels per acre.

Table 1: Common waterhemp control and soybean yield with residual herbicides

Herbicide Rate Application time 5/27/15 6/10/15 6/26/15 7/8/15 9/29/15 Yield
Dual II Magnum 1.5 pints per acre PRE 99% control 96% control 91% control 85% control 81% control 43 bushels per acre
Dual II Magnum 1.5 pints / 1.0 pints per acre PRE / POST 99% control 98% control 96% control 97% control 95% control 49 bushels per acre
Outlook 18 fluid ounces per acre PRE 99% control 96% control 85% control 73% control 71% control 40 bushels per acre
Outlook 14 fluid ounces / 10 fluid ounces per acre PRE / POST 99% control 98% control 97% control 97% control 94% control 51 bushels per acre
Warrant 1.6 quarts per acre PRE 99% control 91% control 82% control 69% control 62% control 32 bushels per acre
Warrant 1.6 quarts / 1.6 quarts per acre PRE / POST 98% control 95% control 95% control 94% control 90% control 46 bushels per acre
Least significant difference (LSD) p=0.10 -- -- 1% control 1% control 5% control 7% control 7% control 4 bushels per acre

Lisa Behnken, Extension educator; Fritz Breitenbach, former Extension integrated pest management specialist; Jeff Gunsolus, Extension weed scientist and Phyllis Bongard, Extension communications specialist

Reviewed in 2018

Share this page:

© 2020 Regents of the University of Minnesota. All rights reserved. The University of Minnesota is an equal opportunity educator and employer.