Pacific Northwest Plant Disease Management Handbook

Garlic (Allium sativum)-Botrytis Leaf Blight

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Latest revision: 
March 2024

See:

Garlic (Allium sativum) - Neck Rot (Gray Mold)

Cause Botrytis squamosa, a fungus that is a problem only late in the season under high humidity, excessive rain, or irrigation. Does not occur in central or eastern Oregon.

Symptoms A small circular to elliptical, grayish=white leaf spot develops and later becomes brownish and dry.

Cultural control

  • Rotate with non-host crops.
  • Destroy nearby onion or garlic cull piles.

Chemical control At the leaf blight stage, the disease can be checked by applying a fungicide; however, that will not control the neck rot and bulb rot stages of the disease.

  • Bonide Fung-onil is available for home gardens. H
  • Bravo Ultrex (Group M5) at 0.9 to 1.8 lb/A on 7- to 10-day intervals. Do not apply within 7 days of harvest. 12-hr reentry.
  • Carboxamide (Group 7) formulations are registered for use. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action.
    • Endura at 6.8 oz/A on 7- to 14-day intervals. Preharvest interval is 7 days. 12-hr reentry.
    • Fontelis at 16 to 24 fl oz/A on 7- to 14-day intervals. Preharvest interval is 3 days. 12-hr reentry.
  • Dithane F-45 Rainshield (Group M3) at 2.4 quarts/A on 7-day intervals. Do not apply to exposed bulbs. Preharvest interval is 7 days. 24-hr reentry.
  • Scala SC (Group 9) at 9 or 18 fl oz/A on 7- to 14-day intervals for great-headed garlic. When applying alone, do not make more than two (2) consecutive applications of Scala SC without alternating to an equal number of applications of a fungicide from a non-Group 9. Do not apply within 7 days of harvest. 12-hr reentry.
  • 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.
    • Quadris Flowable at 9 to 15.5 fl oz/A. May be applied the day of harvest. 4-hr reentry.
  • Trilogy at 0.5% to 1%. Not labeled for use in Oregon. Do not use above 90°F or when plants are under heat or moisture stress. Do not use when foliage is wet as good coverage is essential. Poor control as a stand-alone product. 4-hr reentry. O
  • Premixed fungicides are available for use. Do not make more than one (1) application of any 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. Preharvest interval is 7 days. 24-hr reentry.
    • Dexter Xcel (Group M3 + 11 +3) at 56 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.
    • Inspire Super (Group 3 + 9) at 16 to 20 fl oz/A on 7- to 10-day intervals with no more than two (2) sequential applications. Preharvest interval is 7 days for bulb onions; 14 days for green onions. 12-hr reentry.
    • Luna Tranquility (Group 7 + 9) at 16 to 27 fl oz/A on 7- to 14-day intervals. Do not make more than two (2) applications before alternating to a fungicide in different FRAC groups (non-Group 7 and non-Group 9). Preharvest interval is 7 days. 12-hr reentry.
    • Merivon Xemium (Group 7 + 11) at 8 to 11 fl oz/A on 7- to 14-day intervals; not registered for use in Washington. Do not make more than two (2) applications before alternating to a fungicide in different FRAC groups (non-Group 7 and non-Group 11). Preharvest interval is 7 days. 12-hr reentry.
    • Pristine (Group 7 + 11) at 14.5 to 18.5 oz/A. Preharvest interval is 7 days. 12-hr reentry.
    • Quilt Xcel (Group 3 + 11) at 17.5 to 26 fl oz/A. May be applied the day of harvest for green onion types; 14 day preharvest interval for dry bulb onions. 12-hr reentry.
    • Switch 62.5 WG (Group 12 + 9) at 11 to 14 oz/A on 7- to 10-day intervals. Do not apply within 7 days of harvest. 12-hr reentry.

Biological control

  • Stargus at 2 to 4 quarts/A plus a nonionic surfactant on 7- to 10-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
  • Prestop on 3- to 6- week intervals. 4-hr reentry. O
  • Romeo at 0.23 to 0.91 lb/A on 7- to 10-day intervals starting prior to infection. Preharvest interval is 0 days. 4-hr reentry. O
  • Serenade Opti (BM02) at 14 to 20 oz/A on 7- to 10-day intervals. Applications can be made up to and the day of harvest. 4-hr reentry. O

Pscheidt, J.W., and Ocamb, C.M. (Senior Eds.). 2024 Pacific Northwest Plant Disease Management Handbook.
© Oregon State University.

Use pesticides safely!

  • Wear protective clothing and safety devices as recommended on the label. Bathe or shower after each use.
  • Read the pesticide label—even if you’ve used the pesticide before. Follow closely the instructions on the label (and any other directions you have).
  • Be cautious when you apply pesticides. Know your legal responsibility as a pesticide applicator. You may be liable for injury or damage resulting from pesticide use.

Trade-name products and services are mentioned as illustrations only. This does not mean that the participating Extension Services endorse these products and services or that they intend to discriminate against products and services not mentioned.

H - Home garden packaging commonly available.     O - Acceptable in organic production.