Waterhemp, Common
(Amaranthus Rudis L.)

Return to Problem Weed Index Page

Table of Contents

1. History
2. Life Cycle
3. Distinguishing Characteristics
4. Control in Corn
5. Control in Soybeans
6. Control in Winter Wheat

History

A member of the pigweed familly, but not native to Ontario. Common waterhemp was first detected in Lambton County in 2002. Tall waterhemp (Amaranthus turbriculatus), a close relative has been in documented in Ontario since the late 1800's and can be found mainly along waterways and beaches.

Life Cycle

Annual, with both male and female plants. Female plants will produce seed for reproduction.

Distinguishing Characteristics

Often confused with red-root or green pigweed at early stages of growth. It is distinguished by its narrow leaves, wavy leaf margins and near hairless leaves and stems with a "smooth to the touch" feel. At maturity, waterhemp is considerable taller than other pigweeds ranging anywhere from 1.5-2.5 m (4.5'-7.5') in height. It will be very tall and narrow in appearance with stem colours ranging from green to red/purple.

Common Waterhemp Pictures
Each thumbnail image links to a larger image

| Top of Page |

---

Herbicide Control in Field Corn

Pre-Emergent Control in Corn

Waterhemp emerges over a long period of time in the spring. A number of soil applied residual herbicides will provide good early season control (Table 1). Certain waterhemp populations in Ontario are resistant to triazine (i.e. atrazine) and group II (i.e. Peak Plus, Summit etc.) herbicides.

Table 1. Waterhemp control in corn using various pre-emergent herbicides.

Active Ingredient	Trade Name	% Control
isoxaflutole/atrazine	CONVERGE	99
s-metolachlor/benoxacor/atrazine	PRIMEXTRA II MAGNUM	99
mesotrione	CALLISTO	98
dicamba/atrazine	MARKSMAN	86
pendimethalin	PROWL	81
dicamba	BANVEL II	72
atrazine	Various Trade Names Exist	0

Post-Emergent Control in Corn

A number of post-emergent herbicides will provide good control of waterhemp (Table 2).

Table 2. Waterhemp control in corn using various post-emergent herbicides.

Active Ingredient	Trade Name	% Control
mesotrione + atrazine	CALLISTO + atrazine	97
dicamba	BANVEL II	95
dicamba/atrazine	MARKSMAN	94
diflufenzopyr/dicamba	DISTINCT	92
atrazine/2,4-D	SHOTGUN	90
mesotrione	CALLISTO	86
bromoxynil + atrazine	PARDNER or KORIL + atrazine	80
primisulfuron-methyl/dicamba	SUMMIT	69
prosulfuron + dicamba	PEAKPLUS	64
atrazine	Various Trade Names Exist	0

Source:

Dr. Peter Sikkema, Ridgetown College, University of Guelph.

Number of Trials:

Tables 1 and 2 are based on a summary of 1 field trial in corn.

Herbicide Rates:

Rates used in this trial are listed in OMAF Publication 75 - Guide to Weed Control.

Weed Stage:

Waterhemp had not emerged at the time of any pre-emergent applications and was in between the 2-14 leaf stage (1-15 cm.) at the time of all post-emergent applications.

What has been your experience?

We want your feedback. Let us know what you have experienced with these or other products, as well as any other effective management strategies.

---

Herbicide Control in Soybeans

Pre-emergent Control in Soybean

Waterhemp emerges over a long period of time and therefore a soil applied residual herbicide will establish early season control, and a post-emergent herbicide may be applied later if needed. Of the soil applied herbicides, products containing the active ingredients of s-metholachor/benoxacor (i.e. DUAL II MAGNUM, BOUNDARY, BROADSTRIKE DUAL MAGNUM), dimethenamid (i.e. FRONTIER) and linuron (i.e. LOROX L) will provide good control of waterhemp (Table 1). It is important to note that waterhemp populations exist in Ontario which are resistant to triazine (i.e. SENCOR) and group II (i.e. Pursuit, First Rate, Pinnacle, Classic etc). herbicides.

Table 1. Waterhemp control in soybean using various pre-emergent herbicides.

Active Ingredient	Trade Name (Rate)	% Control
s-metolachlor/benoxacor + metribuzin	BOUNDARY (High Rate)	97
s-metolachlor/benoxacor	DUAL II MAGNUM	91
linuron	LOROX L (High Rate)	86
flumetsulam/s-metolachlor/benoxacor	BROADSTRIKE DUAL MAGNUM	85
dimethenamid	FRONTIER	83
flufenacet/metribuzin	AXIOM	79
metribuzin	SENCOR (High Rate)	48
imazethapyr + metribuzin	CONQUEST	14
cloransulam-methyl	FIRSTRATE (High Rate)	11
imazethapyr	PURSUIT	0

Source:

Dr. Peter Sikkema, University of Guelph.

Number of Trials:

Table 1 is based on a summary of 1 field trial in no-till soybean.

Herbicide Rates:

Rates used in this trial are listed in OMAF Publication 75 - Guide to Weed Control.

Weed Stage:

Waterhemp had not emerged at the time of all pre-emergent applications.

What has been your experience?

We want your feedback. Let us know what you have experienced with these or other products, as well as any other effective management strategies.

---

Herbicide Control in Winter Wheat

As of 2004, Waterhemp has not been found in any Winter Wheat fields in Ontario. Field studies in corn have shown that the active ingredients of bromoxynil and 2,4-D have good activity on waterhemp. Therefore products like Pardner or Koril, Buctril M, Badge or Mextrol and 2,4-D would be logical herbicides to apply should an infestation occur.

What has been your experience?

We want your feedback. Let us know what you have experienced with these or other products, as well as any other effective management strategies.

| Return to Problem Weed Index Page |

| Top of Page |