How to Manage Pests

Pests in Gardens and Landscapes

Bacterial blight—Pseudomonas syringae

Bacterial blight damage varies depending on the host plant and strain of Pseudomonas syringae involved. On some species, such as California bay and English laurel, injury is normally confined to leaves, causing a leaf blight. Leaf blights cause small black angular spots; large, irregular, brown spots form on leaves. Blossom and tip dieback, vein blackening, leaf spots, or stem cankers are common symptoms on oleander, pine, and poplar. On flowering fruit trees, brown to black lesions on the flowers, fruits, and stems form; branch cankers and brown streaks in the wood may also occur. On other hosts, elongated lesions may appear on twigs and infected tissue may ooze during wet weather. Trees may have gum deposits. Bacterial blight is promoted by prolonged rainy springs. Symptoms may be more extensive in wetter areas.

Identification | Life cycle

Solutions

Prune branches showing dieback and severe blight. Space plants to provide good air circulation. Prune during the dry season when infection is less likely to occur. Do not wet foliage with overhead irrigation; do not overfertilize. Small plants can be protected to some degree by keeping them covered by plastic (or moved under plastic). Plant resistant species if available. If the disease is systemic or cankers appear on the trunk, the tree will probably die and should be removed. If the disease is confined to leaves, damage is not usually serious and trees normally recover. Sprays do not give reliable control.

Pseudomona sp. on lilac
Pseudomonas sp. on lilac
Gumming on almond branch
Gumming on almond branch
Apple blossoms and shoots
Apple blossoms and shoots killed by blight

 

 

 


Statewide IPM Program, Agriculture and Natural Resources, University of California
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