NC State Extension Publications


Trade Name: Lontrel Common Name: clopyralid Formulation: 3 L


Postemergence control of legumes, composites, and other broadleaf weeds in and around Christmas trees, ornamental grasses, and established non-leguminous woody ornamentals in landscape plantings,and field nurseries. Used primarily as a directed spray but may be applied over the top of several conifers and a few other woody ornamental species.

Amount of Active Ingredient Amount by Formulation
3 L
Per Acre 0.09 to .375 lb 4 to 16 oz
Per 1,000 sq. ft. 0.1 to 0.375 oz

Major Weeds Controlled

Many broadleaves in the aster and legume families including clovers, horseweed, ragweed, cocklebur, thistles, locust, kudzu, vetches, and other related species. Also effective on certain other broadleaf species including smartweed.

Major Weeds Not Controlled

Many weeds not in the plant families listed above including lambsquarters, pigweeds, pokeweed, nightshades, mustards, grasses, and sedges.

For Best Results

Apply to actively growing weeds prior to flower development. Annuals should be less than 4 inches high and perennials should be in the rosette stage. Best application time is mid- to late spring or early to mid-autumn. Application to wet foliage may decrease control. Allow 2 hours drying time after application.

Cautions and Precautions

Do not use over the root zones of sensitive legumes such as acacia, mimosa, or red bud. Do not contaminate irrigation water or water used for domestic purposes. Tree injury may occur with the addition of a surfactant or crop oil. Do not exceed 12 pint per acre on blue spruce and do not exceed 2/3 pint per acre on other species. Total number of applications must not exceed 1.33 pints per acre per year. Avoid drift. Do not make aerial applications.

Residual Activity

Clopyralid has a half-life of a few weeks to a few months across a range of soil types. Significant residues are not expected after one year, but some plants (particularly legumes) are very sensitive to the herbicide. Chlopyralid persists in grass clippings and compost. Do not use clippings from treated areas in compost or as mulch.

Volatility and Leaching Potential

Low volatility. Not strongly adsorbed to soil so it has a high leaching potential, but field studies indicate that leaching is limited in mineral soils. Label recommends that this product not be used on very permeable soils (such as sands and loamy sands) with shallow water tables or in areas with sinkholes over limestone bedrock or in areas with severely fractured surfaces.

Symptoms and Mode of Action

Symptoms are similar to those resulting from phenoxy herbicides. Clopyralid is a synthetic auxin. HRAC Group O; WSSA Group 4.

Additional Information

Worker Protection Standards REI: 12 hours
PPE: coveralls, chemical resistant gloves, shoes plus socks, protective eyewear
Manufacturer: Dow AgroSciences EPA Reg. # 62719-305


Professor of Weed Science, Extension Specialist & Department Extension Leader
Horticultural Science

Publication date: June 6, 2016

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