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three seeded mercury weed

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Monday – November 09, 2009

From: Austin, TX
Region: Southwest
Topic: Invasive Plants
Title: Removing three-seeded mercury in Austin
Answered by: Barbara Medford

QUESTION:
ANSWER:

Well, you may have to learn to like Acalypha phleoides (shrubby copperleaf), or be more aggressive. It is native to this part of the state, and therefore very adapted to the rainfall, climate and soil. Since it is perennial, just pulling it off the root is not going to stop it from coming back up, as you have already pointed out. You can't spray it with herbicide, as it would kill all the other dicots or broad-leaved plants (like the straggler daisy) that you already have. If you buy a spray that is for monocots, or grasses, it won't bother the three-seeded mercury, but it could kill some native grasses that you have been cultivating.

The first thing to do is make sure it never has an opportunity to go to seed. Even though it is a perennial that can come up from the roots, it will also propagate itself by the seeds on those tall bracts. This might be a time to break your rule about never mowing; if you mow it before it can seed, and keep mowing it as it sends up more bracts to try to seed again, you might just wear out the food stored in the roots. Doing this for several weeks when the plant is trying to bloom, and thus set seed, could greatly alleviate your problem.

Beyond that is the somewhat labor-intensive, hands and knees on the ground, method of painting the cut stem with a wide spectrum herbicide. Begin with a small bottle of the herbicide and some disposable sponge brushes. Cut each stalk off near the root and quickly, within five minutes before the stalk starts to heal over to protect the roots, paint the cut edge with the herbicide. Be very careful, spilling this could contaminate the soil and kill the other plants, broad-leaf and grasses, and don't spray, for the same reason. This plant is monoecious, which means it has both male and female flowers on each plant, and each plant can carry on creating more plants with no outside help.

From our Native Plant Image Gallery:

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Ministry of Agriculture, Food and Rural Affairs

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

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).

Various Trade Names Exist
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.

Various Trade Names Exist PARDNER or KORIL + atrazine

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.

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.

FIRSTRATE (High Rate) SENCOR (High Rate) SENCOR (low Rate) BROADSTRIKE DUAL MAGNUM LOROX L (High Rate) DUAL II MAGNUM
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.

FIRSTRATE (High Rate) glyphosate (Roundup Ready Soybeans only) CLEANSWEEP BASAGRAN FORTE

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.

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).

Three-seeded mercury, Acalypha rhomboidea

The information on this website is general information only. The Government of Canada, the website contributors and the organizations that they represent do not offer any warranty or guarantee, nor does it assume any liability for any crop loss, animal loss, health, safety or environmental hazard caused by the use of management practices mentioned in this website.

This website lists a number of brand names of pesticides. It is neither an endorsement of the product nor a suggestion that similar products are ineffective.

Consult each product label before you use a pesticide. The label provides specific information on how to use the product safely, hazards, restrictions on use, compatibility with other products, the effect of environmental conditions etc.

The pesticide product label is a legal document. It is against the law to use the product in any other way.