How to Manage Pests

Pests in Gardens and Landscapes

Citrus blast—Pseudomonas syringae

Bacterial blast infections of citrus occur during cool or wet weather during the winter or spring and usually start as black lesions in the leaf petiole and progress into the leaf axil. Once the petiole is girdled, leaves wither, curl, and eventually drop. Entire twigs may die back. Diseased areas are covered with a reddish brown scab. Infections result in small black spots on the fruit.


Pruning out dead or diseased twigs in spring after the rainy period reduces the spread of bacterial blast. Scheduling fertilization and pruning during spring or early summer prevents excessive new fall growth, which is particularly susceptible to blast infection. Bordeaux sprays applied before the first rain may help prevent bacterial blast.

Black lesions
Black lesions in leaf petiole and axil

Withering leaves
Withering leaves

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