University of California
Herbicide Symptoms

Photosystem I (PSI) Electron Diverter

HRAC Group: D

WSSA Group: 22

PSI Electron Diverters are primarily nontranslocated herbicides that are light activated. These are relatively nonselective chemicals used to control all existing vegetation and as preharvest desiccants. PSI Electron Diverters belong to bipyridylium chemistry. These herbicides accept electrons from photosystem I (PSI) and reduce to form an herbicide radical. This radical then reduces other molecules to form extremely reactive and dangerous molecules that readily destroy membrane lipids, chlorophyll, and disintegrated cell membranes allowing cytoplasm to leak, which leads to rapid leaf wilting and desiccation.

Injury symptoms: Injury symptoms can occur within 1 to 2 hours after application, appearing first as water-soaked foliage, which is followed by browning (necrosis) of the tissue. Symptoms will appear most quickly with bright, sunny, and warm conditions at application. Drift injury will appear as speckling or necrotic spots on leaf tissue.

Chemistry Group and Common Names of PSI Electron Diverters
Used in the United States

ChemistryCommon Name
Bipyridylium Diquat
  Paraquat
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