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POTATO DISEASE : Common scab

Conditions for development of potato common scab are dry soil, pH basic to neutral, and temperatures conducive to infestation (20-22°C).

Symptoms of common scab

common-scabSymptoms of potato common scab are quite variable. Usually, roughly circular, raised, tan to brown, corky lesions of varying size develop randomly across tuber surfaces.
Symptoms of common scab potato disease are superficial brownish diameter 5-8mm wounds on the tuber. The blemishes can appear on the surface, raising the peel by 1-2mm (russet scab) or causing slight depressions. Usually potato foliage has no visible symptoms.
But common scab severe damage quality of tubers.

Management and control

Cost common recommendation to prevent of common scab while growing potatoes is using of disease-free seed tubers, crop rotation, and optimal irrigation, while maintaining field capacity suitable for potato cultivation.
For growing good crop of potatoes use a 3-5 year rotation, preferably with legumes. Plant scab-free or treated seed on land free of scab. Use an acidic fertilizer, such as ammonium sulfate, for nitrogen and irrigate adequately especially during tuber initiation.
Neutralizing excessively acidic or alkaline soils may help to reduce levels of common scab.
Maintain good moisture levels in the soil while tubers are developing.
Crop rotation in which potatoes will be planted in the same area only once every 3 or 4 years. Avoid rotating with root crops; instead plant grains, grasses, or legumes.
Chemically treating seed pieces before planting with the fungicide Captan will help reduce seedborne potato common scab inoculum.

Organic potatoes

Blackleg potato disease

Blackleg, aerial stem rot, and tuber soft rot of potato are all similar
diseases cablackleg-potato-diseaseused by several types of soft-rot bacteria Erwinia carotovora.

Blackleg potato disease symptoms are blackening and rotting at the base of the stem of potato plants. Soft, slimy rot often starting at stem end of tuber. It is hollowing above the blackened area.
Other symptoms are stunting and yellowing of the foliage, and upward curling of leaflets.
As the disease progresses the potato plant wilts and dies. The bacteria survive in plant residues remaining in the soil, are transmitted by flow water, and can transmit infection to neighboring plants. The disease penetrates through cracks in the tubers and lenticels.
It is more prevalent during periods of increased temperature and humidity. There is no treatment of blackleg potato disease so prevention is the only measure that can be taken.

Management and control

  • Plant whole seed that is free from blackleg. Plant in well-drained soil, especially when using cut seed.
  • Process cut seed with approved fungicides then plant immediately or suberize it well before planting to reduce infection blackleg potato disease.
  • Always do plant potatoes on fields with at least two or three years between potato crops.
  • Avoid excessive irrigation to prevent seed-piece decay and subsequent stem invasion.
  • Remove potato culls and other plant refuse to avoid insect transmission.
  • Frequently clean and disinfest seed cutting and handling equipment as well as planters, harvesters and conveyers to eliminate contamination.

These simple arrangements can help to prevent your potato plants from infection of blackleg potato disease.


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Bacterial soft rot potato disease

soft-rot-potatoWhile growing potato gardeners face problem of soft rot potato disease. Soft rot potato disease is caused by Erwinia carotovora or Erwinia chrysanthemi (Pectobacterium sp. and Dickeya sp). This potato disease spreads by seed tubers, insects, or irrigation water.
Other than sanitation, planting seed not infested with Erwinia and irrigating with clean water, there are few control options for soft rot.
Potato tubers with soft rot symptoms can dry out and the rotten area becomes hard and wooden. Some investigators have termed this symptom “hard rot,” but this term is not commonly used. Erwinia can survive in this dried out tissue for long periods of time.

Soft rot  on tubers, lesions can be as small as a single eye or involve the entire tuber. The rot is extremely soft and colorless. Although rot of the soft rot bacterium is relatively odor free, secondary organisms usually cause a foul smell.

Management and control of potato soft rot

To prevent soft rot do not over-irrigate fields during the growing potato season.
Harvest only mature tubers when soil temperatures are less than 10C. Minimize mechanical damage during harvest and handling.
Protect tubers from desiccation by sun and wind.

Cool tubers of early cultivars to 10C or lower as soon as possible after harvest then store them at 2 to 5C.  For late potatoes store tubers for 7-10 days at 10-15C to promote wound healing, then lower temperature to 2 – 5oC (7-10C for processing tubers).
Provide good ventilation to prevent low oxygen concentrations and development of moisture films on tuber surfaces.
Do not wash tubers before storage. If washing is necessary before marketing, dry the tubers as soon as possible and package them in well-aerated containers.
When washing use only clean water and change it frequently to reduce the soft rot inoculum level. Control other diseases that predispose tubers to soft rot.


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