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Ministry of Agriculture, Food and Rural Affairs

Purple Top or Aster Yellows

Early symptoms of purple top Purple top symptoms Hair sprout from daughter tubers of affected plants
Click to enlarge.

Beginner

Scientific Name
Aster yellows phytoplasma

Identification
This phytoplasma reduces potato yield and quality by causing discoloured tubers and small tubers.

Aerial tubers may form on affected plants and affected stems may die prematurely.

Terminal growth appears bunched and the leaflets roll up at the margins and develop a purplish colour. The leaves may be rigid at first, but later they wilt. Terminal growth may appear yellowish in some varieties.

Daughter tubers of affected plants may produce hair sprouts.

Often Confused With
Herbicide injury
Psyllid yellows
Potato leaf roll virus

Period of Activity
The period of activity is related to the aster leafhopper infestation of potato fields.

This disease is not common in Ontario potato fields.

Scouting Notes

  • Scouting should start before the rows close.
  • Fields should be monitored at least twice a week.
  • When walking fields, stop at many sites as possible and check plants at random.

Advanced

Scientific Name
Aster yellows phytoplasma

Identification
This phytoplasma reduces potato yield and quality by causing discoloured tubers and small tubers.

Aerial tubers may form on affected plants and affected stems may die prematurely.

Terminal growth appears bunched and the leaflets roll up at the margins and develop a purplish colour. The leaves may be rigid at first, but later they wilt. Terminal growth may appear yellowish in some varieties.

Daughter tubers of affected plants may produce hair sprouts.

Often Confused With
Herbicide injury
Psyllid yellows
Potato leaf roll virus

Biology
The aster yellows phytoplasma is transmitted by the aster leafhopper. This leafhopper acquires the phytoplasma from small grains or weed hosts, but can transmit it to potatoes after 10-21 days. The phytoplasma has a wide host range, including many broadleaf weeds, grasses, grains, vegetable crops, and ornamentals.

The earlier in the season the infection happens, the greater the potential crop losses.

Period of Activity
The period of activity is related to the aster leafhopper infestation of potato fields.

This disease is not common in Ontario potato fields.

Scouting Notes

  • Scouting should start before the rows close.
  • 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
Monitor the aster leafhopper closely.