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.


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.

Common name Amount per acre REI‡ PHI‡
(Example trade name)   (hours) (days)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
When choosing a pesticide, consider its usefulness in an IPM program by reviewing the pesticide's properties, efficacy, application timing, and information relating to resistance management, honey bees (PDF), and environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
  (Quadris) 6–12 fl oz 4 0
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Begin applications before disease development and repeat every 7 to 14 days up to three applications.
  (Penncozeb 75DF) 2–3 lb 24 7
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
  COMMENTS: Applied as a protectant and in mixes, or used in rotation with systemic fungicides for disease resistance management.
  (Orius 3.6F) Label rates 12 See label
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode-of-action group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode-of-action group number; for fungicides with other group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode-of-action group number.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Onion and Garlic
UC ANR Publication 3453


R. M. Davis, Plant Pathology, UC Davis
B. J. Aegerter, UC Cooperative Extension, San Joaquin County
T. Turini, UC Cooperative Extension, Fresno County
A. Ferry-Abee, UC Cooperative Extension, Tulare and Kings counties

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

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