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Potato Disease Identification

There are a number of diseases to be aware of that could affect your potatoes. This page provides a gallery of visual symptoms to help you identify what disease your crop may have developed.

Each disease listed below features a link to further information on the symptoms, conditions and controls.

At Sutton Bridge Crop Storage Research, a combination of techniques are used to provide a very accurate identification of the cause of tuber disease. Contact us for further advice or information.

Our disease and defects poster is also a useful visual summary of what may be affecting your potatoes. Download using the link below.

Download the potato diseases and defects poster

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7 November 2018

Potato Defect Identification

Identify common defects in your potatoes using our simple image gallery


Potato disease gallery

Browse the images below to identify which disease may be affecting your potatoes. Each disease features a link to further information on the symptoms, causes and controls.

Alternaria

Alternaria, also known as early blight, is a mainly soil-borne fungal pathogen that affects potato crops. It is a global disease that has been present in GB crops for many years.

Warm and wet periods favour the disease, and if not controlled, it can cause dramatic leaf loss, leading to yield reductions of up to 30%.

Black dot

Black dot is caused by the fungus Colletotrichum coccodes and although a mild disease it is one of the most problematic blemish diseases of washed, pre-packed potatoes.

It takes its name from the tiny jet black microsclerotia that are just visible to the naked eye both on the blemish and on stem and stolen lesions late in the season.

Blackleg and bacterial soft rot

May cause non-emergence of haulm or stunted, pale green to yellow foliage and blackened stems, while tubers can suffer from black rot from heel end or lenticels. 

The disease is mainly seed-borne and is more readily spread under wet conditions, in field and in store.

Black scurf and stem canker

Rhizoctonia solani is a fungal disease causing stem canker, damping off, black scurf, skin netting and tuber growth distortions.

Black scurf can be soil and seed borne and survives a long time in soil and on volunteers or crop debris. There is no significant proliferation during storage.

Dry rot

Dry rot is the most important fungal rot of potatoes, affecting around 1% of tubers in Great Britain.

It is mainly caused by a group of four Fusarium species, particularly in warm, sandy soils.

Generally, dry rots develop around an initial wound, dehydrating in concentric wrinkles and with white, fluffy mycelial growth.

Brown rot

Potato brown rot poses a serious threat to GB potato production and vigilance is required to prevent its introduction and spread.

Several isolated cases have occurred linked to the presence of the causative bacterium (Ralstonia solanacearum) in certain watercourses and it is a notifiable disease.

Common scab

Common scab, caused mainly by Streptomyces scabiei, is an unsightly blemish disease that can affect any crop where tubers experience a dry surface during the critical stage of three to six weeks after tuber initiation.

Consequently it can be especially problematic where irrigation is not available.

The disease has little effect on storability and does not develop in store.

Dickeya

The bacteria Dickeya spp. (formerly Erwinia chrysanthemi) and Pectobacterium spp. (formerly Erwinia carotovora) all cause tuber soft rots.

Pectobacterium atrosepticum has traditionally been considered the main cause of blackleg in the UK, but in recent years certain Dickeya species have been increasingly found to cause wilts and stem rots in warmer seasons, especially when the temperature rises above 25ºC.

They are particularly suited to the warmer southerly potato growing regions of Europe and Mediterranean countries, but incidences of up to 30% are also being observed in Britain.

Gangrene

Gangrene is a slow-growing fungal disease of stored potatoes favoured by cool climates.

Early symptoms are small round, dark depressions that may appear dark grey to brown. These grow to resemble thumb impressions and may overlap, leaving ridges in between.

Wrinkles tend to stretch across, rather than the concentric rings expected with dry rots.

Late blight

Late blight remains the single most important potato disease, costing the industry an estimated £50 million a year in crop protection chemicals during a typical blight pressure season.

Over the last few years, two dominant strains, 13_A2 and 6_A1, have been found. These strains can infect a plant more rapidly, so limiting the curative effects of some fungicides.

You should also refer to our Fight Against Blight pages for guidance.

Latent and mild mosaic viruses

These viruses cause a range of foliar symptoms from none (latent) to very weak, through to a pronounced mosaic, with some distortion of the leaflets.

These viruses have an important economic impact since they affect yield and quality.

Latent crop infections provide a reservoir of inoculum that may infect adjacent crops.

Pink rot

Pink rot can be devastating, especially in hot dry years. However, wet soil is required for infection.

It only attacks the underground plant, sometimes causing wilt late in the growing season.

Tubers may appear sound at loading but breakdown can begin in a matter of weeks.

Potato Leafroll Virus (PLRV)

PLRV was once the most common virus in seed stocks and also caused the greatest yield loss in ware crops. Early symptoms are often slight and may be missed.

It is transmitted by aphids in a persistent manner; once an aphid acquires the virus it is infective for life. The most effective protection against colonising aphids include current flush-through seed certification schemes combined with roguing and aphicides.

Powdery scab

Powdery scab is a fungal blemish disease of potatoes.

The 'powder' is comprised of spore balls that are released into the soil and can survive up to ten years. These release motile zoospores that infect root hairs.

Powdery scab is also a vector of Potato Mop Top Virus, a cause of spraing.

Ring rot

Ring rot is caused by the bacterium Clavibacter michiganensis subsp. sepedonicus. The disease is favoured by cooler climates.

Already established in northern and Eastern Europe, the disease could readily establish under UK conditions.

Symptoms are much more likely to be seen in tubers and are somewhat similar to those of brown rot.

Rubbery rot

Rubbery rot is caused by the fungus Geotrichum candidum. It is more commonly found in first early and second early crops.

Tubers are damp and feel rubbery when squeezed. The skin of affected tubers may have tufts of grey or white mycelia.

Cut tubers exude water and may have a vinegary, sour milk smell.

Silver scurf

Silver scurf is a ubiquitous fungal blemish disease of potatoes.

Infection can originate from seed tubers, the soil or from spores remaining in store. Symptoms are normally present at harvest but the disease develops in store.

Affected skin is weakened, prone to scuffing and can wrinkle due to moisture loss. 

Skin spot

Skin spot is a fungal disease of potato tubers which is generally symptomless until after approximately two months of storage, when the infected tissue begins to show spots on some varieties.

This unsightly blemish reduces market value, but even processing crops might require extra peeling to remove well developed symptoms.

Potato Mop Top Virus (PMTV)

PMTV is one of two viruses that causes spraing in potato.

Infections are commonly associated with tuber internal blemishing (see also TRV).

This is a significant cause of rejections of both ware and processing crops. Symptoms do not increase during storage.

Tobacco Rattle Virus (TRV)

TRV is one of two viruses causing spraing in potato which is most commonly associated with tuber internal blemishing (see also PMTV).

These defects are significant and cause rejections of both ware and processing crops. Symptoms do not increase during storage.

Tobacco Necrosis Virus (TNV)

TNV is a rare tuber blemish disease with no haulm symptoms. The disease is also known as ABC disease named after three symptom categories first described in the Netherlands.

  • A = dark brown, raised patches;
  • B = dark sunken lesions, sometimes in rings/horseshoes;
  • C = light brown, cracked patches.

 Any combination of these symptoms may occur but look for dark coalescing rings, very dark patches, and mild light tan patches. 

Verticillium wilt

Verticillium wilt is a fungal disease of the vascular tissue of potato and most commercial cultivars are susceptible.

The disease is often seen as scattered patches in a field and can result in stunting, premature plant senescence and ultimately a reduced yield.

Plants may lose turgor and wilt, especially on hot sunny days.

Violet root rot

Violet root rot is most commonly seen as a blemish on tubers although roots can be affected.

Affected tubers can be covered in a fine network of purple mycelia that can join to form a net of thickened strands. These will be lost on washing but the purple brown microsclerotia will remain in affected patches.

The margins of these patches are likely to have ragged edges where skin has been undermined. This skin damage may lead to soft rotting by secondary infection.

Wart disease

Tubers, stolons and occasionally leaf stalks are affected by this disease but not roots. 

Tubers may bear cauliflower-like tumours at the eyes, or the whole tuber may become a shapeless, warted mass.

This disease may progress in store even from minute warts not seen at lifting.

Watery wound rot

Watery wound rot or leak is a vigorous rot of lifted tubers caused by a fungus. It is widespread and common but only occasionally serious in a crop.

Affected flesh can be discoloured grey through to brown with a dark margin. It is moist and quickly liquefies.

A fresh cut can smell alcoholic or, if more advanced, fishy.

Potato Virus Y (PVY)

Combined quality and yield losses make PVY the most damaging of the potato viruses.

Depending on virus strain and potato variety, symptoms vary from mild mosaic to severe foliar necrosis to plant death.

The virus can be spread by mechanical contact but is more extensively spread by winged aphids.

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