NC State Extension Publications

Problem

Herbicide injury caused from metribuzin, a photosystem II (PS II) inhibitor.

Symptoms

  • Older leaf interveinal and marginal chlorosis.
  • Older leaf margin curl.
  • Older leaf necrosis followed by dieback.
  • Mottled or interveinal chlorosis develops after necrotic tissues have dropped.
  • Necrosis of young, tender stems exposed to the spray.
  • No root injury.
Metribuzin drift on Knockout rose five days after treatment.

Metribuzin drift on Knockout rose five days after treatment.

B. Lassiter  CC BY-NC-SA - 4.0

Metribuzin on grape five days after treatment.

Metribuzin on grape five days after treatment.

B. Lassiter  CC BY-NC-SA - 4.0

Grape foliage, 14 days after treatment.

Grape foliage, 14 days after treatment.

B. Lassister  CC BY-NC-SA - 4.0

Metribuzin drift on peach foliage five days after treatment.

Metribuzin drift on peach foliage five days after treatment.

J. Neal  CC BY-NC-SA - 4.0

Metribuzin on strawberry five days after treatment.

Metribuzin on strawberry five days after treatment.

J. Neal  CC BY-NC-SA - 4.0

Metribuzin on acorn squash five days after treatment.

Metribuzin on acorn squash five days after treatment.

J. Neal  CC BY-NC-SA - 4.0

Plant Entry and Symptom Expression

Foliar or root assimilated and translocated up the plant. PS II inhibitor injury symptoms from as-triazines first appear as interveinal chlorosis on older leaves within about seven days of application. Sensitive plants receiving high doses will develop necrotic stems. New leaves forming after exposure may develop interveinal or mottled chlorosis.

Similar Problems

PS II inhibitor injury may be confused with:

  • Urea and other PS II inhibitors such as s-triazines.
  • Fast acting, contact herbicides such as paraquat.
  • Chlorosis of growing points caused by ALS inhibitors such as halosulfuron – differentiated by general chlorosis of new growth rather than interveinal chlorosis caused by PS II inhibitors.
  • Mottled chlorosis between leaf veins may resemble damage from foliar nematodes or micronutrient deficiencies.
  • Ozone may cause interveinal chlorosis, bleaching, and necrosis.

Herbicide Mode of Action Category

WSSA – 5
HRAC – C1

Authors

Professor Emeritus
Cobleskill Univ.
Professor of Weed Science, Extension Specialist & Department Extension Leader
Horticultural Science
Assistant Professor
Horticultural Science
Extension Associate, Horticulture
Horticultural Science

Publication date: Dec. 11, 2015

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