Agriculture: Small Grains Pest Management Guidelines

Bacterial Blights

  • Bacterial leaf blight of wheat: Pseudomonas syringae pv. syringae
  • Bacterial leaf streak and black chaff: Xanthomonas campestris pv. translucens
  • Halo blight of oats: Pseudomonas syringae pv. coronafaciens
  • Stripe blight: Pseudomonas syringae pv. striafaciens
  • Symptoms and Signs

    Bacterial blights first appear as small, water-soaked spots. The lesions expand into spots, blotches, or streaks with a characteristic appearance. Bacterial leaf streak affects barley and wheat, occasionally oats. Lesions become brown streaks along leaf veins. Droplets or a shiny film forms on the streaks under damp conditions, leaving yellowish granules or scales upon drying. Black chaff is a blackening of glumes caused by the leaf streak pathogen when wet weather occurs during heading. Bacterial leaf blight affects wheat. Lesions develop into light tan spots, blotches, or streaks. Halo blight affects oats. Light tan spots characterized by a pale green margin (halo) may grow together to form blotches. Heavy infections kill leaves. Stripe blight affects oats. Light tan spots do not have a pale margin, and usually enlarge to form stripes. Heavy infections kill leaves.

    Comments on the Disease

    Blights seldom cause significant damage in California because they develop only during wet weather. These bacteria survive on crop residue, volunteer grains and wild grasses, and grain seed.


    Use clean seed, practice crop rotation, avoid overhead irrigation if blight becomes a problem, and eliminate crop residue.

    Text Updated: 02/07