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How to Manage Pests

UC Pest Management Guidelines


Onion and Garlic

Rust

Pathogen: Puccinia porri

(Reviewed 1/07, updated 6/08)

In this Guideline:


SYMPTOMS AND SIGNS

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.

MANAGEMENT

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/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. AZOXYSTROBIN
  (Amistar) 2–4 oz 4 0
  (Quadris) 6.2–12.3 fl oz 4 0
  MODE OF ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Begin applications before disease development and repeat every 7–14 days up to 3 applications.
 
B. MANCOZEB
  (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.
   
C. MANEB 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.
 
D. TEBUCONAZOLE*
  (Folicur) 3.6 F Label rates 12 see label
  MODE OF ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Use allowed under a Section 18; check with your County Agricultural Commissioner.
 
+ Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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 (for more information, see http://www.frac.info/). 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.

[Precautions]

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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