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Ministry of Agriculture, Food and Rural Affairs

Viruses

Virus infected leaf Virus infected plant Virus fruit symptoms
Click to enlarge.

Beginner

A number of mosaic viruses infect cucurbits including cucumber mosaic, papaya ringspot, watermelon mosaic, zucchini yellow mosaic.

Identification

  • Infected leaves become mottled yellow/green and take on a puckered (drawstring) effect
  • If infected at an early growth stage, the plant will become stunted and malformed; it may also fail to produce fruit
  • Plants infected later in the season will produce mottled, misshapen fruit that often fail to ripen

Often Confused With
Nutrient Deficiencies

Period of Activity
Viruses can be present at any time, although they are most common during periods of heavy aphid infestations.

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.

Thresholds
None.  There are no effective controls for viruses in cucurbits.

Advanced

A number of mosaic viruses infect cucurbits including cucumber mosaic, papaya ringspot, watermelon mosaic, zucchini yellow mosaic.

Identification
Infected leaves become mottled yellow/green and take on a puckered (drawstring) effect.  If infected at an early growth stage, the plant will become stunted and malformed; it may also fail to produce fruit.  Plants infected later in the season will produce mottled, misshapen fruit that often fail to ripen.

Often Confused With
Nutrient Deficiencies

Biology
Depending on the crop, virus diseases may be spread by aphids and/or other leaf-feeding insects, such as the cucumber beetle.  Insects can carry and transmit a virus for their entire life (persistent transmission) or they can acquire a virus during feeding (non-persistent transmission).

In persistent transmission, an insect can become infected after feeding on an infected plant for an extended period of time (at least several minutes to 1 hour).  After an incubation period (sometimes several days or weeks), the insect is able to spread the virus for the rest of its life. 

Non-persistent transmission occurs when an insect lands on and samples plant tissues from many different plants.  The insect picks up the virus from an infected plant and transfers it to the next plant.  As the insect feeds, it clears the virus from its mouthparts and is no longer able to transmit the disease to additional plants.  Soybean aphids are a common vector of many non-persistent viruses.

Period of Activity
Viruses can be present at any time, although they are most common during periods of heavy aphid infestations.

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

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

Management Notes

  • If the infection is caused by aphids, once the problem is identified, the aphids have moved on, making insecticide applications inefficient at controlling the problem.
  • The use of clean seed, resistant varieties and the management of alternative hosts, including weeds, can reduce sources of viruses in the field.
  • Most of the common viruses infecting vegetable crops are non-persistent viruses.