NC State Extension Publications


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Trade Name: Pennant Magnum Common Name: S-metolachlor Formulation: 7.62EC

Preemergence control of yellow nutsedge, annual grasses, and certain broadleaf weeds in nursery (field and container) and landscape plantings of many woody and some herbaceous ornamentals. Also used in Christmas tree transplant beds and field plantings.

Amount of Active Ingredient Amount by Formulation
Per Acre 1.2 to 2.5 lb 1.3 to 2.6 pt
Per 1,000 sq. ft. 0.5 to 1 fl oz
**Do not exceed 4.2 pt (4 lb ai/A) per acre per year [or 1.5 fl oz per 1,000 square feet per year]

Major Weeds Controlled

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Most annual grasses, annual sedges, galinsoga, doveweed and black nightshade. Suppression of yellow nutsedge.

Major Weeds Not Controlled

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The following are generally not controlled from seed: dandelion, lambsquarters, bittercress, eclipta, phyllanthus, yellow woodsorrel, wild mustard, Canada thistle, bindweed, bermudagrass, and quackgrass. Purple nutsedge is not controlled. Weak on groundsel and horseweed.

For Best Results

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Apply before weeds emerge or after existing weeds have been removed. To avoid injury to foliage of ornamental plants, treat when plants are dormant or as a directed spray to avoiding contact with young shoots. Use higher rates on organic soils or where nutsedge or a heavy weed infestation is expected. A second application about 2 months after the first treatment will be necessary for suppression of yellow nutsedge. Commonly tank mixed with other herbicides to expand the spectrum of weeds controlled; follow label directions. Tank mixes with some herbicides have been incompatible. Test herbicide mixtures before filling the spray tank.

Cautions and Precautions

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Do not apply over the top when ornamental plants that have tender, young growth or injury and stunting may result. Do not apply more than twice a year. Do not exceed 2.6 pt per application and 4.2 pt per acre per year. Do not use in greenhouses or other enclosed structures. Pennant Magnum can cause temporary foliar burn on some species. Injury to ornamental grasses has been reported.

Residual Activity

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Two to three months of yellow nutsedge suppression, and three to four months of annual grass control can be expected, depending upon the rate, rainfall, and soil type.

Volatility and Leaching Potential

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Relatively nonvolatile. Moderately water soluble but readily adsorbed by soil organic matter. Where soil organic matter approaches 2 percent, leaching is not expected to be significant; however, in sandy soils leaching can occur. Under certain conditions, Pennant Magnum may move off site in surface water. See label for a special surface water protection information.

Symptoms and Mode of Action

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Germinating grasses absorb metolachlor through the shoots just above the seed, whereas dicots absorb it through both shoots and roots. The most common injury symptom is crinkled leaves, in grasses accompanied by unfurled leaves. These symptoms take two to three weeks to develop. When applied to tender, spring growth, contacted foliage can turn water-soaked then brown or black. S-metolachlor inhibits both cell division and enlargement by inhibiting lipid biosythesis. HRAC Group K3; WSSA Group 15.

Additional Information

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Worker Protection Standards REI: 24 hours
PPE: coveralls, chemical resistant gloves, shoes plus socks
Manufacturer: Syngenta EPA Reg. # 100-950


Professor of Weed Science and Extension Specialist
Horticultural Science

Publication date: Feb. 4, 2015

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by NC State University or N.C. A&T State University nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your local N.C. Cooperative Extension county center.

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