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
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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).

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.

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.

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.

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).

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.