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Archive for the ‘Diseases Caused by Fungi’ Category

Powdery Scab Potato disease

Thursday, September 10th, 2009

(Spongospora subterranea)

Powdery Scab is  disease caused by Fungi meet while growing potatoes.
It is present in all potatogrowing areas in temperate zones and in the tropical highlands of Central and South America.

Symptoms of Powdery Scab

Powdery-scabThere are usually no aboveground indications of disease. Initial symptoms are small, light-colour, blister-like swellings on the tuber surface. At an advanced stage, these become dark, open pustules 2 to 10 mm in diameter or larger, containing a brown, powdery spore mass.

Lesions are variable in shape, mostly roundish, and fringed by broken skin. Root galls of up to 15 mm across may form. In large numbers, they reduce plant vigour. When galls are newly formed, their colour is similar to that of normal roots.

Later, as galls disintegrate, the colour rapidly darkens.

Management

Soil fumigation with methane sodium is reported to control powdery scab. Planting in well-drained soils free of disease and a long crop rotation with grasses where disease occurs may reduce incidence.

Plant disease free potato tubers. Resistant potato cultivars exist and should be used.

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Dry rot potato disease

Monday, August 10th, 2009

Dry rotSeveral species of Fusarium cause dry rot potato disease.
Young potato tubers have some resistance to dry rot which slows disease. But dry rot disease progresses noticeably during the last half of the storage season.

The first symptoms of dry rot are usually dark decay on the surface of the tuber. In cases of large lesions the skin becomes wrinkled in concentric rings as the underlying dead tissue desiccates. Internal symptoms are characterized by necrotic areas shaded from light to dark chocolate brown or black.
This necrotic tissue is usually dry and may develop at an injury such as a cut or bruise. The pathogen enters the tuber, often rotting out the center. Rotted cavities are often lined with mycelia and spores of various colors from yellow to white to pink depending on the species of the pathogen.

Management and control of dry rot potato disease

Practically the following procedures will help prevent dry rot.

  • Critical point is to purchase seed that has as little dry rot as possible. Seed should be inspected, preferably during the last months of storage.
  • To minimize injury and promote rapid growth Warm seed tubers should be warmed to at least 50° F before handling and cutting. Cold tubers are very prone to shatter bruising.
  • Clean and disinfect the seed storage before receiving seed. Knives on the cutter should be sharp to make a smooth cut for that easy healing.

Disinfect seed cutting and handling equipment often and clean up well between seed Plow Attachmentlots. Adjust the cutter and sort tubers to provide 2-ounce seed pieces that will provide substantial nutrition to the developing plant, even if some rot develops.
Get rid obviously rotted tubers before they reach the cutter.

  • Treating seed pieces with fungicide helps prevent dry rot and other diseases caused by seed pathogens.
  • Protect the seed tuber from affect of wind and sunlight during planting because dehydration greatly weakens them. Cutting pieces should be planted within 24 hours.
  • Harvest tubers after skins are set and when pulp temperature is greater than 50° F. Use antibruise practices when harvesting and piling potatoes.
  • If using a postharvest fungicide, be certain that the coverage is adequate to protect the entire surface of the tuber. Use the volume of water and fungicide rate specified on the label.
  • Allow a period for wounds to heal before dropping the temperature in storage. There should be good air circulation, high humidity (greater than 90%), and temperature around 55° F.
  • For prevention of condensation on the tubers drop the temperature slowly and store tubers as cool as possible, considering your intended market.
  • Monitor storages often for dry rot. Never place tubers with dry rot symptoms in storage because doing so spreads disease.