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UC Pest Management Guidelines


Onion scales affected by sour skin turn soft and tan.

Onion and Garlic

Sour Skin

Pathogen: Pseudomonas (Burkholderia) cepacia

(Reviewed 1/07) , updated 1/07) )

In this Guideline:


SYMPTOMS AND SIGNS

Individual leaves affected by sour skin wilt and die back. Internally, leaves develop a soft, watery rot. The fleshy scales associated with infected leaves rot to form a tan-colored slimy ring in the bulb. Adjacent rings may remain healthy. The neck of infected bulbs is soft when pressed.

COMMENTS ON THE DISEASE

Sour skin occurs on both onion and garlic, but usually is only a concern on onion. The pathogen, which survives in the soil, is splashed onto leaves and into the neck of the onion during rain or overhead irrigation. The bacteria gain entrance through wounds and watersoaked tissue. Once in a leaf, bacteria continue to grow down the blade into the bulb. Warm weather favors disease development; optimum temperatures for disease development are over 85°F.

MANAGEMENT

Cultural Control
Switch from sprinkler to furrow irrigation once onions start to bulb (bulbing occurs about the time the bulb is twice the diameter of the neck). Make sure onion tops are well matured before harvesting. Provide for quick drying following topping, especially if temperatures are high.

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Onion and Garlic
UC ANR Publication 3453
Diseases
R. M. Davis, Plant Pathology, UC Davis
B. J. Aegerter, UC Cooperative Extension, San Joaquin County
Acknowledgment for contributions to Diseases:
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara/San Luis Obispo counties
R. E. Voss, Vegetable Crops, UC Davis

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