Effective Management of Waterhemp
Introduction
• Adequate control of waterhemp* is a large concern among
farmers in the Midwestern U.S.
Figure 2. Percentage of waterhemp seedbank that remained viable
after being buried for 1, 2, 3, and 4 years in a study near Ames, IA
(Buhler and Hartzler, 2001).
60
% of Original Seedbank
• This update will review some recent advances in waterhemp
management with tips to improve control.
50
40
30
20
10
0
Year 1
1. Understand waterhemp biology
• Waterhemp has an extended germination period relative to
many other common weed species (Figure 1).
• Seed viability declines rapidly with time (Figure 2).
• Waterhemp is very competitive for yield in soybeans.
• Only seeds in the top inch of soil will successfully germinate
and emerge.
• Herbicide resistant populations can spread rapidly, so
cultural control is very important.
Figure 1. Emergence of waterhemp in no-till plots in a study near
Ames, IA (Refsell and Hartzler, 2009).
Year 4
2. Include cultural practices in your
management strategy
Tillage
• Because waterhemp emerges only in shallow soil and the
seedbank is relatively short lived, tillage practices can reduce
waterhemp populations.
• A University of Missouri field study showed a large reduction
in late-season waterhemp density associated with deep or
conventional tillage (Figure 3).
• Tillage may not be a practical method to help manage
waterhemp on farms vulnerable to soil erosion.
500
400
300
200
100
May 1
June 1
July 1
Aug 1
* Some taxonomic references recognize two waterhemp species, tall
waterhemp and common waterhemp. From a management standpoint, the two species are indistinguishable and here are referred to
collectively as waterhemp.
DuPont Pioneer Agronomy Sciences
Late Season Waterhemp Density
(plants/plot)
Density (plants/m2)
Year 3
Figure 3. Effect of tillage on late-season density of pigweed species
(Bradley, 2014).
600
0
April 1
Year 2
10
8
6
4
2
0
Deep Tillage
Conv.
Tillage
Min.
tillage
Minimum
Tillage
No-Till
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Row Spacing and Population
3. Use soil-applied herbicides
• Narrower row spacing can help suppress waterhemp growth.
• Use of a soil residual herbicide applied pre-plant or preemergence, or as a layered residual tankmixed with a postemergence application, can greatly improve waterhemp
management (Bradley 2013).
• Pre-plant or Pre-emergence (before cracking stage):
DuPontTM Enlite®, DuPont Envive®, Zidua®, Fierce®,
Outlook PRO®, Authority® or Valor products®.
• Layered or Post-Emergence Residual (before V3
stage): DuPont Cinch®, Zidua, AnthemTM, Prefix®
• Use of full labeled rates is recommended to improve the
consistency and duration of control. Always read and follow
product label guidelines.
• In a University of Missouri research study, late-season
waterhemp density in no-till soybean production was
significantly reduced with narrower rows (Figure 4).
• Greater soybean plant density can also reduce waterhemp
growth.
• A seeding rate of 160,000 seeds/acre reduced end of season
waterhemp density by 50% compared to a seeding rate of
130,000 seeds/acre (data not shown).
Figure 4. Effect of soybean row spacing and herbicide program on
late-season pigweed density (Bradley, 2014).
Waterhemp density (plants/plot)
30
7.5" row spacing
25
15" row spacing
20
30" row spacing
15
10
Low carrier
volume can
reduce control
as taller weeds
prevent
adequate
herbicide
coverage of
smaller weeds.
5
0
PREfbfbGly+PPO
gly+ppo
PRE
PREfbfbGly+PPO+Residual
gly+ppo+residual
PRE
4. Carefully manage postemergence
herbicide applications
Good to excellent control of waterhemp is possible with the help of
soil applied herbicides.
Bradley, K. 2014. Recommendations for the Management of Resistant Weeds in 2014
and Beyond. Univ. of Missouri Extension.
http://weedscience.missouri.edu/extension/pdf/resistant%20weed%20management%
202014.pdf
Bradley, K. 2013. Waterhemp Management in Soybeans. United Soybean Board.
http://takeactiononweeds.com/wp-content/uploads/2014/01/waterhemp-managementin-soybeans.pdf
• Timing:
• Target applications to 3-6” tall weeds.
• Tankmixes:
• PPO Group 14 (Flexstar®, Ultra Blazer®) herbicides can
improve broadleaf control if applied properly.
• Minimum of 15 GPA (Figure 4).
• Addition of NIS at 1 qt/100 gallons has been shown to
improve consistency of control.
• Spray Pressure:
• Use spray pressure that will assure optimum coverage
while minimizing off-target movement.
• Full labeled rates:
• Improves consistency of control.
Buhler, D.D. and R.G. Hartzler. 2001. Emergence and persistence of seed of
velvetleaf, common waterhemp, woolly cupgrass, and giant foxtail. Weed Science
49:230-235.
Refsell, D.E. and R.G. Hartzler. 2009. Effect of tillage on common waterhemp
(Amaranthus rudis) emergence and vertical distribution of seed in the soil. Weed
Technol. 23:129-133.
Cinch®, Envive® and ®Enlite are registered trademarks of DuPont. All products are trademarks of their manufacturers. The foregoing information is of a general nature and is provided
for informational use only. Please contact your Pioneer sales professional or your herbicide supplier for management suggestions specific to your operation.