Iris Yellow Spot Virus(IYSV) disease : Coalesced lesions on onion leaf
Pathogen: Tomato Spotted Wilt Virus (Tospo virus group)
Symptoms
Lesions can coalesce making unusual, irregular shaped, larger lesions that girdle a leaf and and causes premature death of the plant. The symptoms are more pronounced on flower stalks. Infected leaves and stalks lodge during the latter part of the growing season.
Disease development
Onion thrips (Thrips tabaci) transmit IYSV in a persistent manner. Disease severity is positively correlated with thrips populations in the field. This virus is not seed transmitted. Over-wintering onions, volunteers from prior productions, infected transplants and alternate hosts can all serve as sources of both vector and virus.
Disease management
The disease is transmitted by thrips (Thrips tabaci) which is a major pest of onion. Uproot the virus infected plants and destroy by burning. The insect vector can be control by spraying of insecticides Fipronil 5 % SC @ 0.15 %, Deltamethrin 2.8 % EC @ 0.1 % before flowering and spinosad 2.5 % SC @ 0.1 % or neem oil @ 0.4 % and Beauveria bassiana @ 0.4 % in onion seed crop.
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