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Tomato Viruses - Reference - Ontario Crop IPM

By Dale Cowan, CCA-ON Senior Agronomist, Southern Co-operative Services

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Viruses

CUCUMBER MOSAIC / TOMATO MOSAIC / TOBACCO MOSAIC / TOMATO SPOTTED WILT

Identification The symptoms vary between viruses, cultivars and conditions. Interaction between viruses may occur, complicating visual diagnosis.

Cucumber Mosaic: The virus may cause a distinct narrowing (shoestring) of young tomato leaves, which may look similar to 2,4-D type injury. Plants may be stunted and produce little or no marketable fruit. Some leaves may be mottled.

Tomato Mosaic and Tobacco Mosaic (ToMV and TMV): In tomato, light and dark green mottling (mosaic) of the leaves. Leaflets are small and distorted (narrow and pointed “fernleaf” symptoms). Fruit set may be reduced. The fruit wall may show internal browning. Green and ripe fruit may show yellow blotches and necrotic spots. These viruses are also involved in another disease of tomato called streak or single streak. The leaves show longitudinal brown streaks on the leaves and petioles, and dark blemishes on the fruit. With a combined infection of TMV and potato virus X, a more severe disease, double streak, occurs. Both diseases also show leaf mottling.

Tomato Spotted Wilt: Symptoms vary. Young tomato foliage may turn purplish-brown (bronzing) and later develop numerous small, dark spots. Plants may be stunted or show one-sided growth.

Often Confused With Herbicide Injury (The shoestring effect caused by the cucumber mosaic virus may look similar to 2,4-D type injury. Shoestring can be distinguished from other virus or herbicide injury symptoms by its narrow, tendril-like leaflets.)

Biology Cucumber mosaic virus has over 800 plant species as hosts. Weeds in and around the field can serve as virus reservoirs.

Tobacco and tomato mosaic viruses can be seed borne, but can also survive in infected crop debris.

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Tomato Spotted Wilt virus has a wide host range, including many greenhouse crops, ornamentals, weeds, and field vegetable crops.

Period of Activity Cucumber mosaic is spread by aphids. Thrips are a vector for tomato spotted wilt. The presence of these diseases usually follows periods of high aphid or thrips activity. The mosaic and streak viruses are spread mechanically.

The time for concern for cucumber mosaic and tomato spotted wilt is transplant through harvest; tomato mosaic is seeding through harvest.

Scouting Notes While scouting for other diseases, take note of any mottled, stunted or puckered plants. Record the scope and location of any infected areas.

Visual diagnosis of specific viruses can be difficult. Rapid diagnosis can be obtained through the Pest Diagnostic Clinic at the University of Guelph, or in some cases through test kits.

Thresholds None established. There are no effective controls for viruses in tomatoes.

Management Notes

• Control weed hosts in and around the field. • Ensure transplants are virus-free. • Pigweeds, nightshades and related weeds, milkweed, purslane, chickweed and many other

plants are alternative hosts to the cucumber mosaic virus.

Acknowledgements

http://www.omafra.gov.on.ca/IPM/english/index.html

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