By David Marks
Potato Blackleg is a relatively common disease of potatoes in the UK and is caused by the bacteria Erwinia carotovora var atroseptica.
It is almost always caused by infected tubers and for this reason it’s essential to buy your potato seed from approved merchants.
Even so, there is no guarantee that the potato seeds are unaffected although the risk is much reduced. As potato sets, it is almost impossible to detect ones which are infected with Blackleg.
SYMPTOMS OF POTATO BLACKLEG
The disease attacks the plants very early in the growing season, it’s not unusual for affected plants to show signs of the disease as early as mid June. Foliage will prematurely start to turn yellow and the leaves will turn inwards. If you look at the plant you will see that the base of the stem is a black or dark brown colour and the flesh of the stem is starting to rot. If left in the ground the infection will spread up the plant causing it to collapse completely.
Unusually, the disease normally only affects individual plants. This is because the infection is from the potato tuber and does not easily pass from one plant to another. As well as the stems and leaves showing signs of infection the original seed potato itself will start to rot at the top. The plant will probably not have produced have potatoes underground but if it has these are likely to show signs of rot.
HOW TO PREVENT POTATO BLACKLEG
Because it is very difficult to identify infected potato sets when you plant them, prevention is limited to removing infected plants as soon as the disease is noticed. Burn the foliage and any tubers making sure that all trace of them is removed. Even if a tuber from an infected plant looks to be in good condition still burn it. Tubers take some time to show signs of infection.
HOW TO TREAR POTATO BLIGHT
There is no cure for potato blackleg when your plants are infected. Your only option is to dig up all traces of the plants and tubers then destroy them by burning.