Pyridine Herbicides

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Pyridine Herbicides (a.k.a. pyridine carboxylic acid herbicides) are a family of herbicides that include:[1]

Persistence in the Environment

Gardeners are warned against pyridine herbicides because they "do not readily break down in compost."[2]

"The active ingredients of most concern are aminopyralid, clopyralid, and picloram. These herbicides eventually break down due to heat, exposure to sunlight, moisture, and microbial action. However, the primary factor in their degradation is aerobic microbial action. Breakdown is particularly slow in manure and compost piles, due to lack of oxygen. These compounds may persist for as long as several years in certain situations."[3]

Aminocyclopyrachlor, marketed as Imprelis, is also named as one of the problematic herbicides in this family. "Ohio State University researchers found that when grass was treated with aminocyclopyrachlor and composted, it degraded by about 60 percent over 200 days, with plenty of the active ingredient remaining to do damage to susceptible crop plants - including beans, cucumbers, and tomatoes."[2]

Plant Injury Symptoms

Plants harmed by pyridine herbicides may show symptoms such as poor seed germination; twisted growth; twisted, cupped, and elongated leaves; misshapen fruit; reduced yields; and death (especially in seedlings in young plants).[3]

Susceptible Plants

Plants that are susceptible to pyridine herbicides include:[3]

Imprelis Recall

Imprelis, made by DuPont with the active ingredient aminocyclopyrachlor, was approved for use in every U.S. state except California and New York in August 2010, but was recalled one year later, on August 4, 2011, "following thousands of complaints that the treatment kills trees."[4]

Articles and resources

Related SourceWatch articles


  1. Classification of Herbicides, Accessed September 24, 2011.
  2. 2.0 2.1 "Imprelis Imperils? Pesticide Residues in Compost are Damaging Plants," Organic Gardening, Vol. 58:6, p. 56.
  3. 3.0 3.1 3.2 Pat Hipkins, Pyridine Herbicide Carryover: Causes and Precautions, Virginia Cooperative Extension, Accessed September 24, 2011.
  4. Jonathan Stempel, "EPA halts sale of DuPont's Imprelis herbicide," Reuters, August 11, 2011, Accessed September 24, 2011.

External resources

External articles