UC IPM: UC Management Guidelines for Rust on Onion and Garlic

UC Pest Management Guidelines

Onion and Garlic

Rust

Pathogen: Puccinia porri

(Reviewed 1/07, updated 1/07)

In this Guideline:

Symptoms
Comments on the disease
Management

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/Acre

R.E.I.+

P.H.I.+

(trade name)

(hours)

(days)

When choosing a pesticide, consider information relating to environmental quality.

AZOXYSTROBIN

(Amistar)

2–4 oz

(Quadris)

6.2–12.3 fl oz

MODE OF ACTION: A QoI (Group 11)¹ fungicide.

COMMENTS: Begin applications before disease development and repeat every 7–14 days up to 3 applications.

MANCOZEB

(Penncozeb) 75DF

2–3 lb

MODE OF ACTION: A QoI (Group 11)¹ fungicide.

COMMENTS: Applied as a protectant and in mixes, or used in rotation with systemic fungicides for disease resistance management.

MANEB 75DF

2–3 lb

MODE OF ACTION: A multi-site contact (Group M3)¹ dithiocarbamate fungicide.

COMMENTS: Applied as a protectant and in mixes, or used in rotation with systemic fungicides for disease resistance management.

TEBUCONAZOLE

(Folicur) 3.6 F

Label rates

see label

MODE OF ACTION: A DMI (Group 3)¹ triazole fungicide.

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 until the harvest may take place. In some cases the R.E.I. exceeds the P.H.I. The longer of these two intervals is the minimum time that must elapse before harvest may take place.
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. For more information, see http://www.frac.info/.

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 Co.
Acknowledgment for contributions to the diseases section:
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara/San Luis Obispo counties
R. E. Voss, Vegetable Crops, UC Davis

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How to Manage Pests

UC Pest Management Guidelines

Onion and Garlic

Rust

Pathogen: Puccinia porri

SYMPTOMS

COMMENTS ON THE DISEASE

MANAGEMENT

PUBLICATION