NC State Extension Publications

Problem

Herbicide injury by Synthetic Auxins (SA) including 2,4-D, mecoprop, amniopyralid, clopyralid, dicamba, triclopyr and others. Crop injury may result from misapplication, spray drift, vapor drift, contamination (spray tank, measuring containers, fertilizer, etc.), and carryover in soil, mulch, hay, etc.

Symptoms

  • Acts only on broadleaf plants.
  • Epinastic twisting and downward curving of fully turgid (not wilted) stems and petioles.
  • Malformed leaves may be curled, cupped, strap-shaped or twisted.
  • Chlorosis on new growth progressing to older tissue as plant senesces.
tip necrosis caused by root uptake of aminocyclopyrachlor

aminocyclopyrachlor injury to cryptomeria from root uptake.

J. Neal  CC BY-NC - 4.0

tip chlorosis and necrosis

aminopyralid spray drift injury to cryptomeria 21 days after treatment.

B. Lassiter  CC BY-NC - 4.0

Clopyralid carryover to tomato.

Clopyralid carryover to tomato.

K. Jennings  CC BY-NC-SA - 4.0

Clopyralid carryover to bell pepper.

Clopyralid carrover to bell pepper.

K. Jennings  CC BY-NC - 4.0

Clopyralid carryover to bell pepper.

Clopyralid carrover to bell pepper.

K. Jennings  CC BY-NC - 4.0

treated plant on right is yellowed with tip dieback

Aminocyclopyrachlor injures conifers from root uptake. The arborvitae on the right was exposed via root uptake. Photo take 4 months after treatment.

J. Neal  CC BY-NC-SA - 4.0

Triclopyr spray drift on rose one day after treatment.

Triclopyr spray drift on rose one day after treatment.

B. Lassiter  CC BY-NC-SA - 4.0

Tricolpyr spray drift on rose 21 days after treatment.

Tricolpyr spray drift on rose 21 days after treatment.

J. Neal  CC BY-NC-SA - 4.0

2,4-D spray drift on rose three days after treatment.

2,4-D spray drift on rose three days after treatment.

B. Lassiter  CC BY-NC-SA - 4.0

2,4-D spray drift on rose 21 days after treatment.

2,4-D spray drift on rose 21 days after treatment.

J. Neal  CC BY-NC-SA - 4.0

2,4-D + MCPP + Dicamba spray drift on rose five days after treat

2,4-D + MCPP + Dicamba spray drift on rose five days after treatment.

J. Neal  CC BY-NC-SA - 4.0

2,4-D ester vapor drift on rose, about four weeks after exposure

2,4-D ester vapor drift on rose, about four weeks after exposure.

J. Neal  CC BY-NC-SA - 4.0

Clopyralid spray drift on rose 14 days after treatment.

Clopyralid spray drift on rose 14 days after treatment.

B. Lassiter  CC BY-NC-SA - 4.0

2,4-D spray drift on willow oak three days after treatment.

2,4-D spray drift on willow oak three days after treatment.

J. Neal  CC BY-NC-SA - 4.0

2,4-D ester volatility injury to willow oak one day after treatm

2,4-D ester volatility injury to willow oak one day after treatment.

J. Neal  CC BY-NC-SA - 4.0

Plant Entry and Symptom Expression

Foliar applied and translocated throughout the plant. Symptoms of injury will be visible on new growth stems, petioles and then leaves within 48 hours of exposure; followed by chlorosis in about 7-10 days concluding with growth cessation of shoots and roots in about four weeks. Foliar absorption may occur through vapor drift if the ester formulation is applied. Root absorption is also possible in porous soils. Certain synthetic auxin herbicides, such as aminopyralid and aminocyclopyraclor, are more persistent in the soil and are more likely to be absorbed by root uptake than other SA herbicides.

Likely ways crops could be exposed to damaging levels of auxinic herbicides:

Vapor drift

Spray drift

Soil residual / carry-over

2,4-D amine

H

2,4-D ester

H

H

aminocyclopyraclor

H

H

aminopyralid

H

H

dicamba

H

M

picloram

H

H

triclopyr amine

H

triclopyr ester

M

H

Key (likelihood of exposure): H = high, M = moderate, L = low

Similar Problems

Synthetic auxin injury may be confused with symptoms from:

  • Desiccation – loss of cell turgor pressure; salt accumulation.
  • Diflufenzopyr (Distinct) – auxin transport inhibitor; buildup of IAA.
  • Acetolactate synthase (ALS) inhibitors such as imazapic (Cadre, Plateau, and others) and imazapyr (Arsenal, Chopper, and others) also cause cupped foliage but ALS-treated plants lack curled or twisted growth.
  • Certain aphids and other piercing/sucking insects can induce cupped and curled foliage. Such insect injury is distinguished from SA herbicide injury by the presence of the pest and lack of systemic symptoms on other plant parts.

Herbicide Mode of Action Category

WSSA – 4
HRAC – O

Authors

Retired Professor, SUNY Cobleskill
Professor of Weed Science and Extension Specialist
Horticultural Science
Assistant Professor
Horticultural Science

Publication date: July 13, 2015

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