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Potato blackleg is a common bacterial disease of potatoes, which causes black rotting at the stem base. Initial infections cause stunted growth and yellowing stems.
Healthy potato (left) and one infected with potato blackleg (right). Image: RHS, Horticultural Science
Blackleg is a disease caused by the bacterium Pectobacterium atrosepticum. It is one of the earliest potato diseases to appear, you may see symptoms as early as June, especially in wet years.
This disease only infects potatoes.
You may see the following symptoms:
There is a number of control measures that do not require chemicals:
There are no chemical controls available to gardeners for blackleg.
Blackleg is caused by the bacterium Pectobacterium atrosepticum (previously known as Erwinia carotovora pv. atroseptica). It is one of the few important plant diseases caused by bacteria in the UK.
This disease normally comes into gardens (or allotments) via infected seed potatoes. Infected plants are removed from commercial seed crops, but a small number of infected tubers escape detection and seed lots will usually contain a few of these. These infections in the seed tubers are usually symptomless and impossible for gardeners to detect.
If the infected plants that grow from these are not removed from the crop promptly, the disease will spread through the soil to infect new plants. The bacteria survive over winter principally in infected volunteer tubers and potato plant debris. They also survive at low levels in the root zone of some weeds. The bacteria may also be carried through the crop by insects or on contaminated soil.
However, in gardens it is infected seed potatoes that are the most important source.
Potato black scurf and stem cankerPotato tuber rotsPotato scabPotatoesVerticillium wilt
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