Mercury, Three-seeded
(Acalypha rhomboidea Raf.)

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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 spurge family. Three-seeded mercury has become a serious weed in agricultural fields where group 2 herbicides (e.g., Pinnacle, Pursuit etc.) have been repeatedly used. This weed can cause serious crop losses in cereal, corn and soybean fields.

Life Cycle

Annual, reproducing only by seed.

Distinguishing Characteristics

In the seedling stage this weed is often confused with redroot and green pigweed. It is distinguished from pigweed species by its glossy bronze-green leaf colour, leaf margins with irregular, rounded teeth and clusters of greenish flowers at each axil. In addition Three-seeded mercury has round cotyledons, whereas green and redroot pigweed has very long and slender cotyledons.

Three-seeded Mercury Pictures
Each thumbnail image links to a larger image

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Herbicide Control in Field Corn

Pre-Emergent Control in Corn

A pre-emergent herbicide containing the active ingredient atrazine will provide very good control of three-seeded mercury (Table 1).

 

Table 1. Three-seeded mercury control in corn using various pre-emergent herbicides.

Active Ingredient	Trade Name	% Control - Sikkema	% Control - Swanton
dicamba/atrazine	MARKSMAN	99	--
mesotrione	CALLISTO	97	--
atrazine	Various Trade Names Exist	97	98
dicamba	BANVEL II	14	--

Post-Emergent Control in Corn

Again, products containing the active ingredient atrazine as well as Distinct, PeakPlus and Summit provide effective control of emerged three-seeded mercury (Table 2). Pardner or Koril (applied alone) and Banvel II do not control three-seeded mercury.

 

Table 2. Three-seeded mercury control in corn using various post-emergent herbicides.

Active Ingredient	Trade Name	% Control
atrazine	Various Trade Names Exist	99
dicamba/atrazine	MARKSMAN	99
diflufenzopyr/dicamba	DISTINCT	99
atrazine/2,4-D	SHOTGUN	99
bromoxynil + atrazine	PARDNER or KORIL + atrazine	99
primisulfuron-methyl/dicamba	SUMMIT	99
prosulfuron + dicamba	PEAKPLUS	83
dicamba	BANVEL II	71
mesotrione	CALLISTO	0

Source:

Dr. Peter Sikkema and Dr. Clarence Swanton, University of Guelph.

Number of Trials:

Table 1 is based on 4 field trials in Ontario, 2 conducted by Dr. Peter Sikkema and 2 conducted by Dr. Clarence Swanton.

Table 2 is based on 3 field trials in Ontario conducted by Peter Sikkema.

Herbicide Rates:

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

Weed Stage:

Three-seeded mercury had not emerged at the time of any pre-emergent applications and was in between the cotyledon to 8 leaf stage 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.

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Herbicide Control in Soybeans

Pre-emergent Control in Soybean

If growing no-till soybeans, a pre-plant glyphosate burndown should control any emerged seedlings. FirstRate or the high rate of Sencor should provide excellent residual control of three-seeded mercury. Broadstrike Dual Magnum has proven to be inconsistent as it has offered excellent control in some trials, while performing poorly in others.

 

Table 1. Three seeded mercury control in soybean using various pre-emergent herbicides.

Active Ingredient	Trade Name (Rate)	% Control (Sikkema)	% Control (Swanton)
cloransulam-methyl	FIRSTRATE (High Rate)	99	--
metribuzin	SENCOR (High Rate)	98	--
metribuzin	SENCOR (low Rate)	88	75
flumetsulam/s-metolachlor/benoxacor	BROADSTRIKE DUAL MAGNUM	92	57
linuron	LOROX L (High Rate)	71	53
flufenacet/metribuzin	AXIOM	64	--
imazethapyr	PURSUIT	58	--
dimethenamid	FRONTIER	14	--
s-metolachlor/benoxacor	DUAL II MAGNUM	13	--

Post-emergent Control in Soybean

Control of three-seeded mercury has been fairly inconsistent with many of the post-emergent herbicides. FirstRate and Classic would appear to be the best option for post-emergent control of this weed.

Table 2. Three seeded mercury control in soybean using various post-emergent herbicides.

Active Ingredient	Trade Name (Rate)	% Control (Sikkema)	% Control (Swanton)
cloransulam-methyl	FIRSTRATE (High Rate)	93	--
chlorimuron-ethyl	CLASSIC	93	--
fomesafen	REFLEX	83	55
glyphosate	glyphosate (Roundup Ready Soybeans only)	73	80
imazethapyr	PURSUIT	78	42
thifensulfuron-methyl	PINNACLE	78	13
imazthapyr + bentazon	CLEANSWEEP	75	--
acifluorfen	BLAZER	68	19
bentazon	BASAGRAN FORTE	53	9

Source:

Dr. Peter Sikkema and Dr. Clarence Swanton, University of Guelph.

Number of Trials:

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

Table 2 is based on a summary of 6 field trials in Ontario, 4 conducted by Dr. Peter Sikkema and 2 conducted by Dr. Clarence Swanton.

Herbicide Rates:

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

Weed Stage:

Three-seeded mercury had not emerged at the time of all pre-emergent applications and was at the cotyledon to 8 leaf stage for 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.

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Herbicide Control in Winter Wheat

Not a very common weed in winter cereals due to its emergence being in the spring when many winter cereals are beginning to fill in and "shade out" many annual species. A limited number of products have been tested, of which MCPA and 2,4-D appear to offer adequate control (Table 1).

Table 1. Three-seeded mercury control in winter wheat with various post-emergent herbicides.

Active Ingredient	Trade Name (application timing)	% Control
2,4-D Amine	Numerous Products Exist	85
MCPA Amine	Numerous Products Exist	83
mecoprop	MECOPROP or COMPITOX	71
dicamba	BANVEL II	70
bromoxynil	PARDNER or KORIL	13

Source:

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

Number of Trials:

Tables 1 is based on a summary of 1 field trial in winter wheat.

Herbicide Rates:

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

Weed Stage:

Three-seeded mercury was at the cotyledon to 8 leaf stage at the time of application.

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.

 

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