Mop top virus causes spraing in only a few varieties. It may cause a range of other tuber and haulm symptoms in other varieties, generally with little economic effect. Occasionally transmitted through seed in the second year after infection.

Symptoms

Tubers: Brown or blistery external rings only or both external rings and internal spraing. Rings may encircle whole tuber, often concentric. Cracking, russetting and deformation may occur.

Haulm: Most commonly aucuba or bright yellow spots and markings, often V shaped, e.g. Pentland Javelin. Sometimes pale green V shaped markings, e.g. King Edward. Less frequently stunted mop-like plants with leaves bunched and margins wavy or rolled, e.g. Ulster Sceptre.

Conditions

Transmitted in soil by powdery scab fungus, and most prevalent in cool, damp soils of seed growing areas. Foliage symptoms most marked in cold springs.

Control

When practical, seed growers should eliminate plants and tubers with symptoms and avoid infected soils. Control of powdery scab will control the virus