Pacific Northwest 1998 An Online Guide to Plant Disease Control

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OSU Extension Office
 
Garlic (Allium sativum) -- Rust
 
Cause: Puccinia allii on garlic, leeks, shallots, onion and wild Allium species. This fungus has caused major epidemics in California and some losses in Arizona. California isolates did not infect leek, shallot or elephant garlic. However, P. allii in Europe is extremely damaging on leek.

This fungus may overwinter on dead plant material, in soil, or on wild hosts. When seed cloves collected from rust-infected garlic plants were planted in studies by the University of California, none of the plants that grew from these cloves developed rust. The rust is autoecious and same-season reinfection by urediospores is common. Severe losses are reported when excessive rain, fog, or irrigation are present. Highest infection rates occur at cool temperatures (50-59° F) and 100% relative humidity. Temperatures below 50° F and above 75° F inhibit the disease. No resistant garlic lines have been identified.

Symptoms: Initial symptoms include small white to yellow flecks and spots. The spots enlarge and become oval to elongate or diamond shaped and take on an orange cast as uredia develop. Later in the season, black oval to elongate telia develop. These telia may or may not break through the epidermis. Telia of a related species, P. asparagi, found occasionally on onion, tend to be dark brown rather than black. Heavily infected plants have an orange cast, outer leaves may yellow and wither prematurely, and bulb size may be reduced.

A garlic field infected with rust.

Close-up of rust infections on garlic.

 
Cultural control:
  1. Rotate out of Allium crops for 2-3 years and destroy all volunteers and Allium weeds.
  2. Use clean seed.
  3. Plants stressed by too much or too little water and too much nitrogen are more susceptible to damage from this rust.
Chemical control:
  1. Dithane F-45 Rainshield at 2.4 quarts/A on 7-day intervals. Do not apply to exposed bulbs. Do not apply within 7 days of harvest. 24-hr reentry.
  2. Folicur 3.6F at 4 to 6 fl oz/A on 10- to 14-day intervals. Do not apply within 7 days of harvest. 12-hr reentry.
  3. Manex at 1.6 to 2.4 quarts/A on 7-day intervals. Do not apply to exposed bulbs. Do not apply within 7 days of harvest. 24-hr reentry.
  4. Orius 3.6F at 4 to 6 fl oz/A on 10- to 14-day intervals. Do not apply within 7 days of harvest. 12-hr reentry.
  5. Quadris at 6 to 12 fl oz/A on 7- to 14-day intervals. Do not apply more than one (1) foliar application of Quadris or other Group 11 fungicide before alternating with a different mode of action. May be applied the day of harvest. 4-hr reentry.
References:
  1. Richardson, M. J. 1990. An annotated lost of seed-borne diseases. Fourth Ed. ISTA, Zurich, Switzerland.
  2. Schwartz, H. F. and S. K. Mohan. 1995. Compendium of Onion and Garlic Diseases. St. Paul. MN: APS Press.
Content edited by: John Greisbach and Cynthia M. Ocamb on January 1, 2009
 
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