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Ministry of Agriculture, Food and Rural Affairs

Leaf roll and Net necrosis

Symptoms of seed-borne infection Symptoms of field infection
Click to enlarge.

Beginner

Scientific Name
Potato leaf roll virus(PLRV)

Identification
Symptoms of leaf roll originating from infected seed tubers

  • Plants are stunted with upright growth habit
  • Lower leaves are rolled up, pale green and leathery.
  • Eventually lower leaves die and upper leaves turn yellowish
  • Yield reduction is severe

Symptoms of leaf roll originating from aphid transmission during the current season.

  • Plants are slightly stunted.
  • Upper leaves are rolled up, yellowish or pinkish
  • Usually, daughter tubers develop net necrosis that renders tubers unmarketable.

Net necrosis symptoms:

  • First appear as light to dark brown strands of discoloration in the flesh at the stem end of the tuber
  • Net necrosis may not be apparent at harvest, but develops in storage.
  • Yield reduction is not significant unless infection occurs very early in the season

Often Confused With
Mosaic virus

Period of Activity
Plants from infected tubers show symptoms within a month after emergence. Current season infection develops after aphids probe on potato plants.

Scouting Notes

  • Scouting should start shortly after emergence.
  • Fields should be monitored at least twice a week. 
  • When walking fields, stop at many sites as possible and check plants at random

Thresholds
No thresholds are established.

Advanced

Scientific Name
Potato leaf roll virus(PLRV)

Identification
Symptoms of leaf roll originating from infected seed tubers

  • Plants are stunted with upright growth habit
  • Lower leaves are rolled up, pale green and leathery.
  • Eventually lower leaves die and upper leaves turn yellowish
  • Yield reduction is severe

Symptoms of leaf roll originating from aphid transmission during the current season.

  • Plants are slightly stunted.
  • Upper leaves are rolled up, yellowish or pinkish
  • Usually, daughter tubers develop net necrosis that renders tubers unmarketable.

Net necrosis symptoms:

  • First appear as light to dark brown strands of discoloration in the flesh at the stem end of the tuber
  • Net necrosis may not be apparent at harvest, but develops in storage.
  • Yield reduction is not significant unless infection occurs very early in the season

Often Confused With
Mosaic virus

Biology
The PLRV survives in infected seed tubers, cull pile tubers and tubers left in the field after harvest. The potato leafroll virus (PLRV) is introduced into a potato field either by planting infected seed tubers or by aphid transmission during the current season. Plants from infected tubers show symptoms first on lower leaves within a month after emergence. Current season infection develops after aphids probe on potato plants.

The virus can be spread by several aphid species that colonize potato, with the green peach aphid being the most efficient. The insect vector is absolutely essential to spread because mechanical transmission does not occur with PLRV. The aphid must acquire the virus by feeding on a PLRV infected plant. Then the virus must circulate from the gut of the aphid, through the circulatory system until it finally gets into the salivary glands, from which it can be excreted when the aphid feeds on healthy plants. Only after this has happened can the aphid spread the virus. This sequence of events may require 24 hours or more to occur. Once an aphid becomes infected, it remains so for the rest of its life. Winged aphids spread the virus over long distances. Wingless aphids spread PLRV within the field.

Period of Activity
Plants from infected tubers show symptoms within a month after emergence. Current season infection develops after aphids probe on potato plants.

Scouting Notes

  • Scouting should start shortly after emergence.
  • Fields should be monitored at least twice a week. 
  • When walking fields, stop at many sites as possible and check plants at random

Thresholds
No thresholds are established.

Management Notes

  • Use certified seed potatoes with the lowest virus level allowed by the certification program.
  • Monitor fields for aphid activity and time insecticide applications.
  • Rogue and destroy infected plants including tubers in seed fields.
  • Control weed hosts such as mustard and shepherd's purse, which can harbor the virus, in field borders.
  • Control volunteer potato plants and eliminate cull piles to reduce inoculum sources.