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Archive for the ‘Diseases Caused by Fungi’ Category

Pink Rot Potato disease

Thursday, September 10th, 2009

(Phytophthora erythroseptica )

Pink rot is most severe occurs while growing potatoes at soil temperatures of more than 20°C in water-logged soils. It is generally not a major problem.

Symptoms of Pink Rot

Although the disease may cause a wilt with stem decay and potatoes leaf chlorosis, usually only tubers have symptoms of dark brown, water-soaked discoloration and sometimes a rubbery texture.
The colour change of cut potato tuber surfaces is characteristic. Within 5 to 20 minutes, these turn from a nearly normal colour to pink and later to black.

The rot is accompanied by a faint vinegar-like smell. Small lesions at harvest may go undetected but grow during storage, although the disease does not spread in potatoes storage.

Management

This soil- and seed-borne disease is enhanced by excessively wet soil conditions and is controlled by improving drainage.

The potatoes disease can be eliminated by fumigating infested soil, complemented with metalaxyl 5G at planting time and the use of healthy potato seed tubers.

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Late Blight

Thursday, September 10th, 2009
Symptom of late blight on the potato leaf.
Image via Wikipedia

(Phytophthora infestans)

Late blight is disease occurs while growing potatoes and caused by Fungi.
Although control measures exist, late blight remains the most serious fungal disease in most major potato production regions.

Symptoms of Late Blight

Water-soaked lesions appear on foliage that, within a few days, becomes necrotic, turning brown when dry or black when wet.

Under damp conditions, white mildew like sporulation is visible, especially on the lower surface of leaves. A pale yellow margin often forms around leaf lesions. Lesions on stems and petioles are black or brown.

Stem lesions are brittle and stems frequently break at the point of the lesion. Under certain conditions, wilting can occur on stems with lesions.
Disease is favoured by temperatures between 10 and 25°C, accompanied by heavy dew or rain.
POtatoes tubers infected by spores washed by rain from the leaves and stems into the soil have brownish surface discoloration.

Sections cut through tubers show brown, necrotic tissues not clearly differentiated from the healthy portions. Later secondary rot organisms develop in blighted tissue and rots spread in storage.

Management

Sources of inoculum are neighboring fields of potato or tomato, volunteer plants, and cull piles.

Riptide 6 Week Pest ControlThe last two sources can be removed. Soil survival occurs wherever the sexual stage (resting oospores) occurs as a result of the presence of both the A1 and A2 mating types, which can lead to early infections.

Once infection occurs in a field, control is a function of host resistance and spraying, mediated by the environment.


Potatoes growers should check with local extension agents for information on forecasting systems or spray schedules that maximize fungicide efficiency and resistance levels of cultivars. There are cultivars with various levels of resistance.
Both protective and systemic fungicides are available, but the latter should only be used according to regional or national strategies that have been developed to minimize the development of resistance in the pathogen.
To prevent tuber infection when growing potatoes, plants should be well hilled, foliage completely sprayed during the growth period, and vines permitted to mature and die naturally or be killed before harvest.

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Wart potato disease

Thursday, September 10th, 2009

(Synchytrium endobioticum)

Wart is potatoes disease caused by Fungi.

Wart or black wart is widely distributed in temperate and high altitude tropical regions with cold and rainy climates. It may cause considerable yield loss where races of the fungus occur for which resistance has not been introduced. The disease is often associated with powdery scab and does not develop in warm or dry soils.

Symptoms of Wart

Tumors of any size up to several centimetres may develop on stems, stolons, and tubers.

Symptoms usually develop below-ground, but under wet conditions they may appear on stems and foliage. Initially, tumors are white to brownish or of the same colour as normal tissue. Tumors blacken with age and may rot because of secondary organisms. Aboveground warts are green, reddish, or purple, depending on variety.

Management

Varieties that are resistant to races of the fungus should be used. Reduce wart incidence with long crop rotations (5 years or more) in combination with resistant varieties.

Prohibiting the shipment of tubers, particularly seed from infested regions, is effective in limiting disease spread.

Seed of resistant varieties grown in infested soil can spread the disease as well as movement of infested soil or manure adhering to tuber surfaces, farm machinery, or other equipment.

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