Why has the base of the stems turned black on my potatoes?
Posted by Dobies Staff on 28 October 2014 11:23 am

Blackleg is a bacterial disease that is a common and wide spread, often appearing from June onwards, especially on heavy clay soils, under warm humid conditions and in wet seasons. The disease is encouraged by wet soil conditions and potatoes should only be planted in a well-drained soil that does not become waterlogged.

The leaves at the top of the plant may be small and curl upwards. Foliage of an affected plant turns yellow and the shoots collapse. The base of the stem becomes black and rots, although occasionally one or two healthy stems develop. The plant may die before any tubers form but any which have already developed show a brown or grey slimy rot inside starting at the heel end. As soon as the symptoms are first seen affected plants and tubers should be destroyed but do not add them to the compost bin.

If severely infected tubers are stored they will decay, but those only slightly infected may show no symptoms and, if planted will introduce the infection the following season. Healthy tubers can be infected at lifting time through direct contact with a diseased tuber. Therefore, once the disease has appeared lift the rest of the crop carefully at harvesting and store only healthy tubers.

The practice of cutting potato tubers to make them go further can increase the risk of an attack. Only plant certified seed potatoes and do not replant tubers from an infected crop.

The varieties Charlotte, Gemson and Kestrel show some resistance to this disease.


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