How to Manage Pests
UC Pest Management Guidelines
Onion and Garlic
Pathogen: Puccinia porri
(Reviewed 1/07, updated 6/08, pesticides updated 6/16)
In this Guideline:
Rust is primarily a disease of garlic, although onion, leeks, shallots, and wild species of Allium are hosts. Small, reddish to dull orange oval-shaped pustules develop on leaf blades. Reddish airborne urediospores are copiously produced within the lesions. Later in the growing season, the lesions may appear dark because black teliospores develop within the pustules. Heavily infected leaves turn yellow and may collapse prematurely. When infection is severe, bulb size and quality are reduced.
COMMENTS ON THE DISEASE
Rust is a sporadic disease that generally causes little or no economic damage. Since 1998, however, rust has caused severe damage in some garlic-growing areas. Apparently, the disease only damages onions when they are planted next to a heavily infected garlic field. The fungus probably overwinters on garlic and volunteer Allium crops.
Rotate away from Allium crops for 2 to 3 years and destroy volunteer Allium plants during this period. Fungicides may be warranted if more than a few pustules develop on plants.
UC IPM Pest Management Guidelines: Onion and Garlic
R. M. Davis, Plant Pathology, UC Davis
Acknowledgment for contributions to Diseases:F. F. Laemmlen, UC Cooperative Extension, Santa Barbara and San Luis Obispo counties
R. E. Voss, Vegetable Crops, UC Davis