iris yellow spot virus
Beginner
Scientific Name: Tospovirus
Identification
- Characterized by straw coloured, diamond- and spindle-shaped lesions
- On second year crops (e.g. onions from sets or garlic), active lesions may have a yellow halo surrounding a green island of leaf tissue
- Infected plants can produce good quality bulbs; however, under stressful conditions, plants will lodge and bulb sizing ceases.
- Has also been detected in other allium crops (e.g. leek, garlic), iris, and weeds (e.g. redroot pigweed, Jimsonweed)
Often Confused with
Botrytis leaf blight
Pelting rain/hail damage
Period of Activity
Onion thrips, the only known vector of iris yellow spot virus (IYSV), are found in all onion-growing regions in Ontario. Thrips favour hot, dry weather conditions and are present throughout the growing season. Disease symptoms tend to appear later in July into August in onion crops grown from seed or transplant. Onions grown from sets and garlic often display symptoms earlier in July.
Scouting Notes
Scout for IYSV as you scout for onion thrips making sure to scout along field edges as well. Lesions often appear on younger leaf tissues, where the majority of thrips feeding occurs.
Thresholds
None established.
Advanced
Scientific Name: Tospovirus
At the end of the 2007 growing season, Iris Yellow Spot Virus (IYSV) was detected on direct seeded and transplant onions in Ontario, leading to the first positive identifications of the disease in Canada. This tospovirus is vectored and persistently transmitted by onion thrips.
Identification
- Characterized by straw coloured, diamond- and spindle-shaped lesions
- On second year crops (e.g. onions from sets or garlic), active lesions may have a yellow halo surrounding a green island of leaf tissue
- Infected plants can produce good quality bulbs; however, under stressful conditions, plants will lodge and bulb sizing ceases.
- This disease has also been detected in other allium crops (i.e. leek, garlic), iris, and weeds (i.e. redroot pigweed, Jimsonweed)
Often Confused with
Botrytis leaf blight
Pelting rain/hail damage
Biology
IYSV is only picked up by 2nd instar onion thrips larvae; however, once infected, thrips are able to transmit the tospovirus for the remainder of their life. Research has shown that IYSV is not distributed uniformly throughout the host plant. The highest levels of IYSV are typically detected in the inner leaves where thrips tend to congregate and feed.
Period of Activity
Onion thrips, the only known vector of IYSV, are prevalent in all onion-growing regions in Ontario. Thrips favour hot, dry weather conditions and are present throughout the growing season. Disease symptoms tend to appear later in July into August in onion crops grown from seed or transplant. Onions grown from sets and garlic often display symptoms earlier in July.
Scouting Notes
Research in the US has shown that disease incidence is the highest at field edges. Scout for IYSV as you scout for onion thrips making sure to scout along field edges as well. Lesions often appear on younger leaf tissues, where the majority of thrips feeding occurs. A good understanding of the onion thrips lifecycle will be beneficial when scouting for IYSV.
Thresholds
None established.
Management Notes
- Be vigilant. If buying set onions talk to your distributor about the disease.
- Be aware. Familiarize yourself with disease symptoms.
- Be diligent. Manage onion thrips populations throughout the season to mitigate the spread of IYSV.
