Beginner

Identification

• Symptoms vary between viruses, cultivars and conditions
• Interaction between viruses may occur, complicating visual diagnosis
• Cucumber Mosaic (CMV):
  • May cause a distinct narrowing (shoestring) of leaves
  • Plants may be stunted and produce little or no marketable fruit
  • Some leaves may be mottled
  • Fruit may be small, and may show some mottling symptoms.
• Tomato (ToMV) and Tobacco Mosaic (TMV):
  • Light and dark green mottling 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
  • Fruit may ripen unevenly.
• Tomato Spotted Wilt (TSWV):
  • Dark streaks may develop on stems.
  • Young tomato foliage may turn purplish-brown (bronzing) and later develop numerous, small, dark spots
  • Plants may be stunted, show one-sided growth, or appear wilted.
  • Fruit may develop ringspots.
• Tobacco Ringspot (TRSV):
  • Transmitted by nematodes, mechanically, or on seed.

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.)

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/thrips activity.  Tomato and tobacco mosaic and the streak viruses are spread mechanically. Tobacco ringspot is transmitted by nematodes, mechanically, or on seed.

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.

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

Advanced

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. Fruit may be small and may show mottling symptoms.

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.  Fruit may ripen unevenly.  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 (TSWV): Young tomato foliage may turn purplish-brown (bronzing) and later develop numerous small, dark spots.  Plants may be stunted, show one-sided growth or appear wilted. Dark streaks may develop on stems.

Tobacco Ringspot (TRSV): Transmitted by nematodes, mechanically, or on seed

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. 

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

Tobacco ringspot infects over 20 plant families.

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.

Tobacco Ringspot is ransmitted by nematodes, mechanically, or on seed.

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.