NC State Extension Publications

Problem

Herbicide injury from ALS inhibitors including imidazolinones (such as imazapic, imazapyr and several others) and sulfonylureas (including sulfosulfuron, metsulfuron, sulmetron, and others).

Symptoms

  • Yellow shoot tips and die-back.
  • Yellow, pink or purple veins.
  • Shorter internodes.
  • “Bottle brushing” roots.
  • In woody plants, ALS inhibitors may cause:
    • foliar cupping.
    • deformed foliage.
    • witches brooms.
    • general die-bac.
Image causes malformed new growth, yellowed and reddish foliage

Image herbicide injury to dogwood.

T. Bilderback  CC BY-NC-ND - 2.0

witches broom of new, stunted shoots on japanese maple stem

Japanese maple damaged by root uptake of imazapyr.

J. Neal  CC BY-NC-SA - 4.0

Knockout rose chlorosis caused by imazapyr spray drift.

Knockout rose chlorosis caused by imazapyr spray drift, two weeks after application.

B. Lassiter  CC BY-NC-SA - 4.0

Reddish pigmentation of main veins on strawberry.

Reddish pigmentation of main veins on strawberry caused by imazapyr spray drift, five days after treatment.

B. Lassiter  CC BY-NC-SA - 4.0

Chinese elm, non-treated.

Chinese elm, non-treated.

J. Neal  CC BY-NC-SA - 4.0

Chinese elm: imazapyr, soil applied.

Chinese elm: imazapyr, soil applied.

J. Neal  CC BY-NC-SA - 4.0

Chinese elm: imazapic, soil applied.

Chinese elm: imazapic, soil applied.

J. Neal  CC BY-NC-SA - 4.0

Cryptomeria, non-treated.

Cryptomeria, non-treated.

J. Neal  CC BY-NC-SA - 4.0

Cryptomeria: imazapyr, soil applied, four weeks after treatment.

Cryptomeria: imazapyr, soil applied, four weeks after treatment.

B. Lassiter  CC BY-NC-SA - 4.0

Cryptomeria: imazapyr, soil applied, four months after treatment

Cryptomeria: imazapyr, soil applied, four months after treatment.

J. Neal  CC BY-NC-SA - 4.0

Cryptomeria: imazapic, soil applied, four weeks after treatment.

Cryptomeria: imazapic, soil applied, four weeks after treatment.

B. Lassiter  CC BY-NC-SA - 4.0

Cryptomeria: imazapic, soil applied, four months after treatment

Cryptomeria: imazapic, soil applied, four months after treatment.

J. Neal  CC BY-NC-SA - 4.0

Crape myrtle, non-treated.

Crape myrtle, non-treated.

J. Neal  CC BY-NC-SA - 4.0

Crape myrtle: imazapic, soil applied, stunted chlorotic foliage.

Crape myrtle: imazapic, soil applied, stunted chlorotic foliage.

J. Neal  CC BY-NC-SA - 4.0

Crape myrtle: imazapyr, soil applied, stunted with new growth.

Crape myrtle: imazapyr, soil applied, stunted with new growth witches broom.

J. Neal  CC BY-NC-SA - 4.0

Crape myrtle: imazapyr, soil applied, stunted with new growth.

Crape myrtle: imazapyr, soil applied, stunted with new growth witches broom.

J. Neal  CC BY-NC-SA - 4.0

Arborvitae, non-treated.

Arborvitae, non-treated.

J. Neal  CC BY-NC-SA - 4.0

Arborvitae: imazapic, soil applied, plant severely stunted.

Arborvitae: imazapic, soil applied, plant severely stunted, chlorotic and necrotic growing points.

J. Neal  CC BY-NC-SA - 4.0

Arborvitae: imazapic spray drift; tip necrosis.

Arborvitae: imazapic spray drift; tip necrosis, stunted and chlorotic growing points, new needles curled back.

J. Neal  CC BY-NC-SA - 4.0

Imazapic spray drift on loropetalum.

Imazapic spray drift on loropetalum. Initial symptoms about two weeks after treatment include stunted and chloratic new growth. Treated foliage on the left, non-treated on the right. Over time tip necrosis, witches broom, and dieback develop.

J. Neal  CC BY-NC-SA - 4.0

Imazapic spray drift on loropetalum, six months after treatment.

Imazapic spray drift on loropetalum, six months after treatment.

J. Neal  CC BY-NC-SA - 4.0

Imazapic spray drift on hydrangea, about 2 weeks after treatment

Imazapic spray drift on hydrangea, about two weeks after treatment. Initial symptoms include stunting and chlorotic new growth. Treated foliage on the left, non-treated on the right.

J. Neal  CC BY-NC-SA - 4.0

proliferation of stunted, yellowed sprouts on a stem.

Imazapyr root uptake injury to Nellie R Stevens Holly. Applied as a mixture of glyphosate + imazapyr to weeds around the plant.

J. Neal  CC BY-NC-SA - 4.0

Plant Entry and Symptom Expression

Foliar and soil absorbed and translocated. Some ALS herbicides have long residual and may affect nearby plants via root uptake or crops planted into previously treated soils. Selected ALS members provide very broad spectrum control while others are quite narrow. Growth cessation within a week of application, followed by chlorosis of the growing points, then tip necrosis, followed by a general decline and death over a period of 3 to 4 weeks. ALS-resistant crops are widely used.

Similar Problems

ALS inhibitor injury may be confused with symptoms from:

  • Glyphosate.
  • Desiccation – loss of cell turgor pressure; salt accumulation.
  • General root decline due to poor soil conditions or soil diseases.
  • In woody plants, witches brooms and deformed or cupped foliage may resemble glyphosate drift or auxin herbicide injury.

Herbicide Mode of Action Category

WSSA – 2
HRAC – B

Useful Resources

North Carolina Agricultural Chemicals Manual

Southern Region Small Fruit Consortium

Southeastern US Vegetable Crop Handbook

Wolfpack Weeds

Weed Management in Nurseries, Landscapes & Christmas Trees Information Portal

Herbicide Handbook, Weed Science Society of America

Applied Weed Science: Including the Ecology and Management of Invasive Plants (3rd Edition), Merrill Ross & Carol Lembi, pages 166, 172-173, 175, 242, 246-248

Authors

Prof. Emeritus, Cobleskill College
Horticultural Science
Professor of Weed Science, Extension Specialist & Department Extension Leader
Horticultural Science
Assistant Professor
Horticultural Science

Publication date: Dec. 14, 2015

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