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Potato Early Blight.



P_potearblight

Potato Early Blight.

Usually appear in

Spring to Summer


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Caused By:-     The Fungus Alternaria solani

Description

Potato Early Blight is a common and sometimes serious disease which also attacks other members of the Solanaceae family. It is caused by the fungus Alternaria solani which has a worldwide distribution and can withstand repeated wet and dry conditions as well as continuously wet conditions. It overwinters as spores on crop debris in or on soil and seed potatoes.
Spores travel long distances on the wind and on landing on leaves of susceptible plants germinate and may penetrate tissues directly through the epidermis, through stomata and or through mechanical injury or insect feeding damage. Moisture and favourable temperatures (15 - 30C) are required for spore germination and infection of plant tissues. Leaf damage begin to form 2 to 3 days after initial infection.
Infection first appear as small irregular dark brown spots on lower leaves and range in size from a pinpoint to 4mm eventually reaching up to 25mm and are often restricted by leaf veins. Characteristic symptoms are dark brown or black lesions with concentric rings on leaves, which produces a target effect. Enlarging lesions are often surrounded by a narrow chlorotic halo. Severely infected leaves eventually wither and die but usually remain attached to the plant. Stem infections may girdle the stem, causing premature death of the plant.
In tubers spores penetrate the epidermis through mechanical injuries to the skin and is unlikely to penetrate undamaged mature skins of the tubers. Infection is most common on immature tubers and those of white- and red-skinned cultivars, since they are highly susceptible to damage during harvest being contaminated with spores from the soil or infected leaves.
Infected tubers show a dark, sunken lesions that are circular or irregular in shape. Infected areas are bordered by raised area of tissue that has a blue-black to purplish discolouration. Underlying tuber tissues are leathery to corky in texture. The fungus may continue to develop in storage and tubers may become shrivelled, but the infection does not seem to spread to other stored tubers. The primary damage of early blight is due to premature defoliation of the plant. Heavy infection early in the growing season can cause large yield losses.
Growth or stress factors that affect susceptibility include vigour of plant growth, soil moisture and nutrition. Some potato cultivars are less susceptible than others, but none has total resistance. Research is continuing with various crosses and genetic engineering to further reduce the effects of this and other fungi. See the British Potato Variety Database.
Weather forecasters often gives an indication when these conditions will appear so that farmers can apply preventative spraying
See also POTATO LATE BLIGHT.


Control

Try to get all the potatoes out from the ground at harvest time.
Water from the base of the plant rather than spraying potatoes.
Removing the foliage early helps prevents the spores from spreading. As long as they are well covered with earth leave the crop alone for at least two weeks to let the blight spores on the surface die and the potatoes develop a thicker skin.
After harvest, check regularly for signs of blight and remove any suspect tubers at once from your store.
Use only good quality seed potatoes obtained from certified suppliers
Fungicides for the control of Potato Early Blight are normally only used in a preventative manner, perhaps in conjunction with disease forecasting. In susceptible varieties, sometimes fungicide applications may be needed weekly. An early spray is most effective. For organic farmers a copper based fungicide is often used.
Practice crop rotation, removal and burning of infected plant debris, and eradication of weed hosts to reduce the number of spores that can infect the plants.
Plant resistant varieties; Visit The British Potato Variety Database for more information.

P_potearblight P_potearblight[2]

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