Diseases By Crop
(Fact Sheets)
Photo Gallery
News Articles/ Disease Alerts
Diagnostic Keys
Virus Weed Hosts/ Rotation Lists
Resistant Varieties
Glossary of Plant Pathology Terms
Vegetable Guidelines
Vegetable IPM Links
Other Vegetable Links
Cornell Plant Disease Clinic


Iris Yellow Spot Virus of Onion

Prepared by Christy Hoepting, Cornell Cooperative Extension Vegetable Program



Iris Yellow Spot Virus (IYSV) is an emerging devastating disease of onion worldwide

• IYSV is a topovirus like Tomato Spot Wilt Virus

• vectored solely by onion thrips

• first detected in seed onion crop in Idaho, 1989

• internationally, IYSV occurs in:
• Israel           • Netherlands(iris)
• Brazil          • Slovania
• Australia

• in the United States, IYSV occurs in:
• Colorado     • California
• New Mexico• Oregon
• Nevada        • Washington
• Utah            • Idaho
• Arizona       • Georgia

Geographic Distribution of IYSV in United States, 2004



• onion seed and bulb
•  crops including
•  volunteers
• other Allium species
•  (e.g. garlic, leek)
• iris
• weeds (i.e. redroot
•  pigweed)

• reduction in yield of large bulb size
•  classes, especially in sweet and red
•  varieties
• reduced seed yield and quality
• delayed crop maturity


Onion Seed Crops

Classic IYSV symptoms: straw-colored dry, tan spindle- or diamond shaped lesions with distinct green centers (or islands) with yellow or tan borders Green islands with yellow centers
IYSV lesions with yellow centers and “double” borders IYS lesions are not diamond-shaped IYSV lesions are coalescing
another variation of IYSV lesions extended IYSV lesions IYSV lesions cause scapes to lodge


Onion Bulb Crops

IYSV lesions on onion leaves (not as distinct as they are on scapes

Less diagnostic IYSV lesions on onion leaves

IYSV-infected transplant seedling
Bulb crop starting to lodge Above-ground symptoms are similar to Fusarium basal rot (insert), but roots are healthy in IYSV-infected plants IYSV lesion on bulb

Scouting for IYSV

• scout fields where transplants were imported from states where IYSV occurs, especially red and sweet varieties

• scout adjacent seed crops and take a close look at volunteer onions, because IYSV lesions tend to be more diagnostic on scapes

•within fields, focus scouting on field edges, stressed areas and in thinner stands

• if you suspect IYSV, contact your local Cornell Cooperative Extension Educator

Photographs were graciously provided by Dr. Lindsay du Toit, WSU, Dr. Howard Schwartz, Colorado State Univ. and Dr. Krishna Mohan, Univ. of Idaho.