How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Initial symptoms of bacterial leafspot are small, water-soaked spots that are visible from both sides of the leaf. The lesions usually are limited by leaf veins and thus have an angular, square, or rectangular appearance. These water-soaked lesions rapidly turn brown and with aging may dry out and become papery and tan. Lesions tend to be relatively small (less than 0.25 inch in diameter) and restricted to leaves. On greenhouse transplants, bacterial blight lesions may develop extensively on the foliage. However, in the field the disease usually is found only on the older leaves that are protected by the plant canopy, except where sprinkler irrigation is used. Under favorable conditions (free moisture), bacterial blight lesions may coalesce and cause considerable blighting of the foliage.

COMMENTS ON THE DISEASE

Pseudomonas syringae pv. apii is a seedborne bacterium. Once introduced into transplant greenhouses, the pathogen can rapidly spread via splashing water. Disease development is favored by warm, moist conditions. Infected transplants carry the pathogen into production fields. In the field, widespread or severe symptoms generally do not develop unless the crop is sprinkler irrigated or subjected to a light frost during the production cycle. The pathogen survives in undecomposed celery residue.

MANAGEMENT

Cultural Control
Use seed that has been indexed free of Pseudomonas syringae pv. apii. Hot water seed treatment (122°F for 25 minutes) will significantly reduce seedborne inoculum, but may reduce seed germination. Using seed that is at least 2 years old can significantly reduce the incidence of this disease.

Disinfect transplant trays because bacteria may survive on dirty trays. In the greenhouse, lower the water pressure from overhead sprinklers because high pressures favor entry of the pathogen into celery leaves. In the field avoid sprinkler irrigation. Excessive application of nitrogen fertilizers appears to favor disease development.

Organically Acceptable Methods
Cultural controls and copper sprays are acceptable for use on organically grown produce.

Treatment Decision
Only copper compounds are registered for use against this pathogen; however, copper has not been very effective.

PUBLICATION

UC IPM Pest Management Guidelines: Celery
UC ANR Publication 3439
Diseases
S. T. Koike, UC Cooperative Extension, Monterey County
R. M. Davis, Plant Pathology, UC Davis
T. A. Turini, UC Cooperative Extension, Imperial County
Acknowledgment for contributions to Diseases:
R. L. Gilbertson, Plant Pathology, UC Davis
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara County

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