Onion (Allium cepa)-Rust

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Cause Puccinia allii, a fungus. Rust is occasionally a problem in organic fields, home gardens, and on onion grown for seed. This fungus may overwinter on volunteer garlic and onions, or on wild hosts. Once rust appears on farm, cropping Alliums year around can lead to serious losses. It becomes critically important to remove production for at least part of the year,

Symptoms The uredinial stage attacks leaves and seed stalks. Light yellow to orange or reddish, powdery pustules develop. As pustules enlarge, the leaves or seed stalks become girdled. Affected tissues at and above the girdling turn yellow and die prematurely, thus reducing seed yield.

Cultural control

  • Rotate out of Allium crops for 2 to 3 years and destroy all volunteers and Allium weeds.
  • Avoid consecutive plantings of onion or garlic.
  • Plow under infected plant residues.

Chemical control

  • Aprovia Top (Group 7 + 3) at 10.5 fl oz/A on 7- to 14-day intervals. Apply no more than two (2) sequential applications alternating with another fungicide with a different mode of action. Preharvest interval is 7 days. 12-hr reentry.
  • Badge SC (Group M1) at 0.75 to 2.75 pints/A on 7- to 10-day intervals. Preharvest interval is 0 days. 24-hr reentry for greenhouse use; 48-hr reentry for all other applications.
  • Demethylation-inhibiting (DMI) Fungicides (Group 3) are labeled for use.
    • Tebustar 3.6L at 4 to 6 fl oz/A on 10- to 14-day intervals. Preharvest interval is 7 days. 12-hr reentry.
    • Tebuzol 3.6L at 4 to 6 fl oz/A on 10- to 14-day intervals. Preharvest interval is 7 days. 12-hr reentry.
  • Miravis Prime (Group 7 + 12) at 10.3 to 11.4 fl oz/A on 7-day intervals. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action. Preharvest interval is 7 days. 12-hr reentry.
  • OSO 5% SC (Group 19) at 3.75 to 13 fl oz/A on 7- to 14-day intervals. Can be applied the day of harvest. 4-hr reentry. O
  • Strobilurin fungicides (Group 11) are labeled for use. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
    • Dexter Max (Group M3 + 11) at 3.2 lb/A on 7-day intervals for dry bulb onion. Do not apply to exposed bulbs. Pre-harvest interval is 7 days. 24-hr reentry.
    • Dexter Xcel (Group M3 + 11 + 3) at 48 to 72 fl oz/A on 7- to 10-day intervals for dry bulb onion. Do not apply to exposed bulbs. Preharvest interval is 7 days. 24-hr reentry.
    • Quadris Flowable at 6 to 12 fl oz/A on 7- to 14-day intervals. May be applied the day of harvest. 4-hr reentry.

Biological control Efficacy in Oregon unknown.

  • Double Nickel LC at 0.5 to to 4.5 pints /A on 3- to 10-day intervals. Can be applied the day of harvest. 4-hr reentry. O

Reference Koike, S.T., Gladders, P., and Paulus, A.O. 2007. Vegetable Diseases: A Color Handbook. St. Paul. MN: APS Press.